What is everyone's engine design preference?

[DavidBoren]

What type or design of engine do you prefer, and why?

Inline six because they are smooth and balanced?

Undersquare for n/a efficiency and torque, versus oversquare for boost and high rpm's?

V8 for that all American thumpy idle, or V6 for the packaging?

What engine type do you prefer, and why?

Also, is there a particular design that is better suited for road racing/pro touring? I know that transmission choice and gearing can be tailored to keep any design of motor in its optimum operating range, but is there a good reason to choose a high revving, oversquare, turbo motor over an undersquare stroker with a positive displacement blower?

[mitch_04]

I would have to say that, on this site, you are going to find mostly V8's for sure. The LS series specifically... they are everywhere, engineered well, parts are available, etc etc etc...

I plan out what my goal is with the vehicle, what I want. I have a '50 Chevy 3600 that will have an inline 6 with fuel injection, well hidden. The idea is an old vehicle with (well hidden) new design. IRS, IFS, etc etc...

I have a '47 that will get an original inline 6, no custom anything. That vehicles a restoration.

I have an '84 Camaro that will be getting a 6.0 LS. It will be boosted (LS's have very strong rotating assembles) and a power house.

I have an '85 C10 that will be getting an inline 5 cylinder. It's more of a "look at me" vehicle, so the originality of a 5 cylinder will fit perfectly with the extreme lowering and custom interior.

So yeah... I'd say match the engine to the design of the project. However, on here, I'm going to go out on a limb and say the LS V8 will be the engine of choice on most builds.

[DavidBoren]

PS. It seems that a lot of people slap in an LS engine "because it works" and call it good. But I asking more of a preference towards one design theory over another, and for what reason.

Example:
I want to build a 359ci LC9 stroker with stock 3.78" bores and a 4" crank. This makes the motor undersquare. The tall, narrow cylinders are better air pumps for naturally aspirated applications, and the long rod design reduces piston speed towards top dead center, which reduces the likelihood of detonation. This should allow for higher compression and more timing.

There is more to that, but I don't want to bore you with a pipe dream engine that I haven't built yet. Those are the kinds of thoughts and explanations I am looking for with this question.

I get that a lot of people just use what works, without having a real preference towards how the results are achieved. But I want to build an engine with the theories I, personally, think makes sense to test whether or not the engine performs how I want it to using the theories I want it to incorporate. If that makes sense.

Building the engine as I want it built, just to see if I want the right things... if the theories that make sense to me actually give the performance I want. Otherwise, I have to re-evaluate my understanding of engines, and how they work, and figure out what it is that I am wrong about. Why what I think should work does (or does not) actually work. That sort of thing.

Anyone else building an engine or picking a particular engine using this approach?

[camcojb]

I know you can take inline 6 off the list for this site... :lol:

[Che70velle]

David, I like the way you think. I'm an engine guy myself, and I'm constantly reading and researching whats out there. I feel that this conversation won't go far on this forum, due to the stupid LS platform being so efficient, and the engineers doing there homework so well, that honestly it's a no brainier for the average guy building a car to choose an LS3, or Ls7 for their project.
My Chevelle, when I bought it had a fresh .030 over 350 with a 350 trans, that worked well, but I wanted to drive this car a lot, so the fuel injection and reliability of the LS series engine was calling my name. Yeah it's mainstream today, but I wanted reliability that an old sbc couldn't give me. Been there done that.
In my younger days, I worked at a shop that built Cup engines, back when people actually outsourced objects in Nascar. Not only did we build engines there, but we raced on the weekends. I was able to learn engine formulas and machine work during the week, and then on the weekend apply what I'd learned. It was a great job for a gearhead like myself.
Later on in life, when funds started to get comfortable, I did my own racing venture, running asphalt late models. I built my own stuff, due to what I'd learned from life's experiences. Absolutely priceless. The engine program that I had to run was perfect for this thread. A lot of homework, trial and error, and money went in to making those engines run. But that was racing.
Not to bust your bubble, but the 4" crank you want to run in your LC9 will increase piston speed, and even with long rods, your piston speed will likely be greater than stock. That block will bore out safely over .100, however.

[mitch_04]

I understand what you're saying (although I haven't studied engines enough to get very in-depth, I stick to short stroke=high rpm, long stroke=torque).

I would think you need to figure out the exact purpose of the car. Autocross or road track would be a big one. Then build around that. A high RPM screamer would probably be wonderful for a long road track, not as useful on a short turn to turn autocross track. You'd have to have it at high RPM which would make gearing incredibly important, similar to racing a 2-stroke motorcycle.

I, personally, love the planning stages of the build. It's only limited by your imagination and, of course, budget. The better planned out build will always make a guy happier in the end, when everything is perfect! Plan away!!!!

[craig510]

I understand what you're saying (although I haven't studied engines enough to get very in-depth, I stick to short stroke=high rpm, long stroke=torque).

I would think you need to figure out the exact purpose of the car. Autocross or road track would be a big one. Then build around that. A high RPM screamer would probably be wonderful for a long road track, not as useful on a short turn to turn autocross track. You'd have to have it at high RPM which would make gearing incredibly important, similar to racing a 2-stroke motorcycle.

I, personally, love the planning stages of the build. It's only limited by your imagination and, of course, budget. The better planned out build will always make a guy happier in the end, when everything is perfect! Plan away!!!!

That all depends on the course. The Goodguys layouts generally have 1 or 2 very slow corners so you need to be in first coming out. Unless you are a racing hero (or paddle shifters) you can't shift 4 times a lap, so RPMs are your friend for higher top speeds. I would love to build a high winding small block for my Falcon.

I am working on a model A which I have a DOHC 4.6 linclon motor for. I got some cams and valve springs for it so it should spin up to 7200. Even if it quits making power at 5900, the extra RPM will keep me off the limiter for a couple more seconds.

[DavidBoren]

Thanks for the replies. And keep them coming.

I hear you about the long stroke increasing piston speed overall, and I figured that it will still be at a higher speed at TDC, than that of the 5.3 piston. But it's no more than that of the other LS engines with a 4" throw, and people spin them plenty fast without detonation issues. So I think I will be ok there. And, I'm looking for torque, with absolutely not a single care of what the peak horsepower ends up being.

Horsepower sells cars, torque wins races.
-Carroll Shelby.

My focus on torque is what led me to the 359 stroker. I'm not all caught up on big cubes or high horsepower. I want a streetable, fun, torquey motor that meets some simple theory criteria I have put together, namely being undersquare.

I want to stay with the 3.78" bore, instead of the 3.9" bore, because the blocks use the same sleeves, so the 4.8/5.3 sleeves have more "meat" than that of the 5.7 sleeves. So the thicker sleeves will handle the extra side load on the pistons from the increased stroke. And the thicker sleeves will handle boost better (if I can ever afford a W180AX for it).

Or at least that's my thoughts on using the 3.78" bore. Wiseco makes forged slugs for the 5.3 with the correct pin height for use with a 4" crank and 6.125" rods, and all the other parts will be stock LS parts.

[Flash68]

Interesting thread. At least it doesn't talk about Camaros... yet.

I really became interested in the Nascar stuff after seeing the teams give away their stuff on the used market after their "life cycle" was used up.

But I also wanted/needed something that didn't have to be rebuilt every 500 miles (1 race).

As much as I would love to play with a 9000 rpm motor, I wanted to gain the needed low and mid range torque and bring the powerband down for durability and less maintenance. So a 4" stroke was used instead of the 3.25" that the Cup cars use.

4.170 x 4.0 = 437"

Of course with the small chamber size of the SB2.2 heads (mine are 51cc, many are in the 40 something range) this made piston design pretty much impossible to achieve 11:1 to 12:1 in order to get to pump gas range. So, to minimize the dish in the piston and keep it "acceptable" according to my engine builder we ended up around 13:1 compression. So, the other pump gas came into the picture... E85. Several stations not too far from me. I am good with that.

Even though a .800-.900 lift cam would be right at home with the heads, we decided to use a milder cam (.660ish net lift) with a lower rocker arm ratio (1.7 instead of 1.9 or 2.0). Again, all to keep things lower maintenance.

I really wanted a toned down Nascar motor with all the cool parts and look but not the rebuild cycle. Time will tell but I think we achieved that without giving up the BIG power. In fact the trade off to gain the torque is what I am really excited about.

640 ft #s out of a pump gas SBC. I'll take it. :)

[DavidBoren]

Thank you, Flash. That is exactly the sort of answer I was looking for. I have heard that it is better for the longevity of the valvetrain to let the cam do the work, instead of compensating with higher ratio rockers. That sounds like a nice engine you have put together. 600+ pounds of torque is no joke.

I was also thinking that using the 4" crank, would slide my power band to the left. I might even use a truck cam in it for the initial build. I'm looking for a relatively tame, yet torquey, motor that I don't need to rev the piss out of.

[bdahlg68]

I know you can take inline 6 off the list for this site... :lol:

Hey hey hey. Not entirely.

[DavidBoren]

The inline six should never be scratched off the list, in my opinion. Between the 2jz and the 6bt, I think that platform has earned its place and proven its worth. I would love to see more inline six swaps, as even the all aluminum Atlas motor can handle boost and respond well.

Just something interesting I found on a big-bang-theory-esque forum discussing undersquare versus oversquare engines from a physics/math/nerd perspective;

Oversquare engines will last longer because the piston travels a shorter distance, therefore it creates less friction. The larger piston also transfers heat to the cooling system better than a smaller piston does. So an oversquare engine creates less heat through friction and transfers the heat to the cooling system better.

Apparently the heat created by friction in the piston rings increases exponentially with stroke length. So if displacement remains equal, the engine with oversquare architecture will waste less energy, every time.

It's kind of funny, or sad, that reading all the advantages of going with oversquare bore-stroke ratio does little to sway my decision to build an undersquare engine. But, I am sure I will find an excuse to build another one, and I will go the other way with it just for the sake of comparison.

Speaking of comparison, here are the two extremes of what is available using stock LS bores and strokes.

Undersquare:
359ci (3.78" bore X 4" stroke)

And

Oversquare:
353ci (4.125" bore X 3.3" stroke)

I think the difference of six cubic inches in total displacement is negligible, so it would be really cool to build and drive both to see if oversquare versus undersquare makes a difference you can feel.

PS. A "square" bore/stroke motor with a displacement of 356ci (the average displacement of the two engines listed above) would have a bore and stroke of 3.842", just to give you an idea of how over or under "square" each of those engines are.

[DavidBoren]

I mentioned that the oversquare engine will generate less heat due to the shorter stroke causing less friction. It also transfers the heat to the cooling system more efficiently because the larger bore cylinder will expose more surface area.

This is also a detriment to the efficiency of combustion in the cylinder. The flame has to spread across a larger surface. A greater portion of the combustion heat/energy is being transferred to the cooling system, rather than being converted into work. And there is a greater loss in pressure per angle of rotation with a shorter/wider cylinder, regardless of rod ratio.

It seems, in my limited understanding, that any benefits of going oversquare, just to gain larger valves, would be negated by the less efficient combustion characteristics. And oversquare cylinders make less efficient air pumps.

So in a naturally aspirated motor, I am going to build it undersquare to capitalize on the efficiency of the tall/narrow cylinders, both as better air pumps and as offering better combustion characteristics.

The small bores/valves can be ported to flow PLENTY enough for a naturally aspirated 359ci (6.0L) motor. TEA stage 2 flows over 300cfm @ .600, which will do just fine for anything less than 7.0L spinning at less than 7k rpm's.

Any thoughts? Am I missing something entirely? The obvious trend in OEM engines is oversquare, unless you count transverse motors which tend to be undersquare for packaging reasons.

You can't really say reliability or service interval is a determining factor in this case due to the fact that there are a lot of high mileage OEM motors still on the road with 4" stroke crankshafts.

And with compression ratios constantly on the rise, you would think that a longer conrod would be preferable to slow the piston near top dead center for less detonation issues. Undersquare engines tend to have longer rods inherent to their design.

So if you can achieve adequate air flow with smaller valves, what is the advantage of being oversquare? I should say that we are staying below 7500rpm's for the sake of this discussion... I have no interest in tickling 10k rpm's.

[Che70velle]

David, speaking only of naturally aspirated engines, the over square method of achieving a set cubic inch goal will be more reliable. Increased rod angle is the biggie, with a taller stroke. The more rod angle you have, the more wear you put on the cylinder wall, and the piston rings/skirt, and it also puts more heat in the engine from friction, which is a no no. A bigger piston will run cooler, all things being equal, due to more surface area for oil splash to cool piston from bottom.
These are things to consider if your building a high rpm endurance engine, which your not, so I say build what you'd like, and enjoy it.
Fun fact...in two absolutely identical engines, one having aluminum heads, the other having cast iron heads, the engine with cast iron heads will make more overall power, due to being able to hold heat in the combustion chamber longer...
Totally off topic, but worthy of discussion also. Logically, you'd want aluminum heads over the iron heads, due to weight, and where the weight is at in the vehicle.

[DavidBoren]

Thank you for the input. I have heard that about iron heads making more power due to combustion chamber heat.

And given that this is a discussion of design theory, I see the inherent detriment of increasing stroke. The side loading and friction/heat increase presents a problem to be resolved, for sure. And is probably (obviously?) best left avoided.

In my particular case, I will have an oversized cooling system with electric water pump and fully boxed/ducted radiator, to handle the heat. And I am going to use the small bore block to capitalize on its thicker cylinder sleeves to address the side loading caused by the 4" stroke.

I also will be running an oil cooler, and I have a small quandary about oil squirters...

Are oil squirters piston coolers, or are they just oil heaters?

They use engine oil to cool the piston. Which puts the heat directly into the oil. Are the pistons cooled enough to really make a difference in detonation issues? Doesn't cooling the combustion chamber decrease power output (as discussed above with iron vs aluminum heads)? Doesn't squirting 75psi of oil UP at a piston that is traveling DOWN add resistance/drag that is otherwise not present?

Also, undersquare engines have better combustion due to small chambers, less surface area, blah blah blah. So if oil squirters do detract from the combustion efficiency, due to heat loss in the combustion chamber, this effect would be naturally counteracted by the undersquare small bore combustion efficiency.

If oil squirters are just to stem detonation, then the long rods inherent to an undersquare motor make them (oil squirts) unnecessary. As long rods slow the piston near top dead center, and naturally reduce detonation issues.

Said another way, do the characteristics of an undersquare motor counteract everything oil squirters are trying to accomplish? Or would the longer stroke, and the friction/heat that comes with it, be in a greater need for added piston cooling?

[Twoblackmarks...]

In my opinion, an short stroke high RPM engine is usually much more fun to drive than an long stroke grunty one.

3.78" Bore is very small for an 2 valve 5.8 liter+, it does not matter if you get "better" combustion chamber, because the valve probably is so shrouded by the cylinder wall that you get poor filling and "looses" combustion efficiency by that. So then you probably need to put in smaller valves to unshroud them. And that 300cfm is probably not flowed on a 3.78" bore, I would guess. But I may be wrong.

But it depends on if you want an 300HP truck engine or an 300+HP fun engine.

I would take the fun engine, a shorter stroke engine that survives some RPM and abuse much more easily than an long stroke grunty engine that runs out of rpm.

I dont think the heat and resistance is such a big deal, unless you are going to run a lot of track, rod angle this and that, the most important is the guy who put the engine together, like Warren Johnson says " The rod only holds the piston" but of course, there is more to it than that..

Piston squirters are good for piston cooling, an 100HP VW engine from the 80s has that, then I would think an 3-4-500+ HP V8 SHOULD have it, it`s almost only just american V8s that dont have it for some reason. Any engine that is going to run continually at high speed/load likes piston coolers. Before people often cut a groove in the rods to get piston cooling, and lubrication.

I dont think there is anything wrong with a 4" stroke, but team it up with an bigger bore than 3.78 and it would be better. Cubes work, that I have experienced.. I have an 4.25 stroke engine.. But is it made for endurance racing, probably not so much..

If you can I would just go for what you think would work and try it, on a side note, most european engines are long stroke - small bore, but they are small engines that "need" the stroke. They often have short rods to, sometimes because of not much room for long. If you are used to US V8s, many european engines seems not so smart put together, from an performance view....

[Ron Sutton]

This is a cool thread ...

IMHO, the I think the key goals are:
A. Wide powerband ... to reduce or eliminate shifting
B. Smooth, non-peaky powerband ... to eliminate surprises to the tires
C. As much power as we can actually use

Concerns:
* The problem with big stroke engines is they build so much torque ... right at the corner exit rpms ... it's hard to not blow the tires away.
* The problem with short stroke engines is often ... not always ... they low end lack torque for optimum acceleration off the corners ... and with the wrong cam, can have a useless, narrow, peaky, high rpm power band.

From my racing experience, if you are in a series with no cubic inch limits, what is both fastest ... and EASIEST TO DRIVE ... is a big bore/medium stroke engine ... designed for a wide, smooth powerband. When I raced in West Coast NASCAR Modifieds, there was no cubic inch limit ... just a carb & tire limit. So we saw every combo including 355"/358", 372/377", 383"/388", 400"/406" & 434" engines. The story went a lot like the 3 bears & porridge.

While the 434" engines made the most power ... torque & horsepower ... they were too hard to drive fast. With 4" of stroke, the drivers were always struggling to get them off the corner optimally. They had to drive them with the proverbial egg under the throttle. That's doable occasionally ... but not consistently lap after lap when your adrenaline is up. The 355"-377" engines had way less tire spin challenges ... but just didn't make enough torque to accelerate the car off the corner optimally. The 383"/388" engines came of the corners hard, but laid over on the straights.

The engines that were "just right" were big bore (4.125"-4.185") & medium stroke (3.750-ish). These 400"-410" engines were dominant. They had optimum torque for the best corner exit on the narrow slick we ran. With the right wide lobe centerline camshaft, they had a wide, smooth powerband that was easy to drive fast & consistently. And the top end power was awesome ... pulling all the way down the straights. In my experience, the 383" & 434" combos are just two different sizes of the same long stroke strategy. Both build their torque down low & run out of stem too early. The 377" & 410" combos are also two different sizes of the same big bore/medium stroke strategy. The 410" just builds more power throughout the entire curve.

For road courses, this is even more critical, as the 10-12 corners are all different. Making the need for a wide, smooth powerband even more critical. I built all of our winning road race engines the same way ... big bore/medium stroke. Getting this strategy right will be even more critical for autocross on TW200 tires.

As over simplified as this sounds ... determining the stroke length you want/need for just the right amount of torque ... is a good starting point. Then design the whole engine around that. I have several versions of a 409" LS engine in development currently. The "tame" versions build 750 hp & the "mean" version will make 900hp. All very drivable on track with a smooth, flat, wide powerband. So that tells you my preference. :)


:cheers:

[Matt@BOS]

I think I prefer big bore and stroke engines for autocross and higher, faster revving smaller cube engines for road courses, at least in terms of fun factor. autocross is a lot more stop-turn-go. I have a Camaro with a 454 cube LS7, and it never lugs out of corners versus my Coyote powered Mustang. However, put the two cars on a road course, and the less powerful Coyote motor is way more fun, despite being slower, simply because you can put your foot down and hold on almost all the time.

[DavidBoren]

I am not trying to argue with anything anyone has said. I think Ron nailed my objectives perfectly. I do have a question about using a 4" stroke and this phenomenon that has been brought up multiple times called "running out of steam"...

From what I have seen, on this forum and other places, the LS7 is a staple of the pro touring community. It has been put in plenty of performance cars that have never had a single complaint about running out of steam.

How many rpms do you use on a road course? The obvious answer is all of them. But seriously, is the 7k redline associated with the LS7, and it's 4" crank, not enough?

Ron says, in "C", to build as much power as you can use. I am building a S-10, it's going to weigh 3000# race weight, I don't think I can use a whole LS7. But it's the go-to engine for pro touring and I am building a pro touring S-10. So I am going to subtract one liter of displacement, but keep the things I like (4" stroke = torque, I like torque). And, at the same time, it provides me with an opportunity to test some design theory that I have for some reason attached myself to.

As for what is more fun to drive. I favor torque here as well. I would rather spin my tires rather than spin the crap out of my engine. I don't roast my tires, and I know spinning tires isn't fast. But I prefer the feeling of taking off in a 500hp duramax diesel truck more than the feeling of "launching" with a 500hp evo8.

I would rather have a car that I have to drive with respect, more than a car I have to abuse. Hunter S. Thompson said that men like big guns and fast cars because they push us to our limits, rather than us pushing the machine to its limits. And with rpm motors, it's like you have to keep them at the upper limit for them to be any fun. But with a torque engine, you have to respect the machine.

Maybe I am just retarded. But I'm under the impression that using a 4" stroke crankshaft will in no way limit my useable rpms.

Is 7000rpms not enough?
Are LS7's hard to drive?

[Rod P]

cool discussion...I'll bite..
engine RPM and to me drive ratio go hand in hand and is very dependent on the track, for the few PT style cars I have built or advised on what I shoot for is an 70-75 mph speed at limiter in second gear..in order to have this i looked at having a 7200RPM limit on my engine, this allows the car to run small events such as Goodguys tracks in first or second only, for example the track in Nashville this weekend was a first gear track, and the finals track in scottsdale is a 1-2 track because it has a long straight that I just reach limit 7200 in second at the end of it....and for larger tracks like Las Vegas motor speed way or Michigan international...I spend a large amount of time in 2-3,,and forth on large straights.....so to me function over form in the engine department

[DavidBoren]

That's the whole point of this, though. I'm trying to make the form of the motor fit the function of the vehicle.

I am trying to get everything working in concert. Engine design theory and architecture, cam profile and useable powerband, transmission gearing, rear axle ratio, suspension and brakes... Isn't the purpose of starting over to do everything over? Everything, for the most part, on the S-10 is set up from the factory to work as a system. Even though it's made from GM's leftover parts bin, some amount of engineering went into making sure that the parts selected meshed together for its intended purpose.

So, for me to change anything, I need to adjust all things. And since there is no single redeeming quality of the original S-10 worth saving (other than its compact chassis/body), I might as well design a whole new system, including an engine specifically designed for the rpm range and powerband I want, and a suspension set up for exactly how I feel a vehicle should handle.

When I see a 10k redline, I think "why" because I know it's possible to make the power sooner. And if you can't make enough power to do... ANYTHING you want... before 7500rpms, then you need less mass, not a higher redline.

My idea of reinventing the 6.0L with a 3.8x4.0 architecture vs the 4.0x3.6 bore and stroke is to shift the powerband left, favoring early torque production. The exact same crankshafts are used in OEM engines that spin to 7k rpms. I have no doubts, whatsoever, that any engine built using this crank will be in any way redline limited.

So, it's up to proper cam selection, valvetrain components, and transmission/axle gearing to best utilize a powerband that both comes on early, and can extend to 7k rpms.

Mind you, the torque will come on early compared to a 6.0L with the 3.6" crank. But it won't subtract from the upper limit of the same mid-stroke 6.0L, given proper valvetrain and cam selection... So I literally do not see a downside to building a undersquare 6.0L motor.

All that needs to be done is porting the heads to provide adequate air flow for six liters of displacement spinning at 7k rpms... Which I know is possible, even with the little valves.

Little valves and little pistons are easy to move, so the rotating mass will be able to rev as high as the big LS7 components, even with the LS7 using titanium.

Everyone always says that they want a broad powerband, and yet it seems no attention is ever paid to broadening it to the left. People go through great lengths to expand the powerband to the right, ever increasing the redline. And engine design and architecture reflects the chase for higher redlines with oversquare engines. Yet you can achieve roughly the same effect starting power production earlier.

3000-8500 powerband is 5500 useable rpms...

So is... 1500-7000...

Things that make you say, "hmm..."

[DavidBoren]

As a side note, using head flow numbers from TEA's website regarding their stage two ported 5.3L heads, and an online calculator provided by Wallace racing, the projected redline where head flow can no longer support the displacement at any higher rpms, is 8000. Playing with different VE inputs got readings between 7300 all the way to 9000. So, no matter what, with properly ported heads, the small bore can support six liters of displacement spinning all the way to 8k...

I have no intentions of spinning it that high, but for the sake of this discussion, I thought it to be relevant.

For comparison's sake, the 353ci oversquare engine proposed earlier, 4.125" x 3.3" bore and stroke, using stock LS7 head flow numbers, gives a max redline of 8,300 to 10,900... depending on what VE values you use.

@RodP, I can get 74.5mph in 2nd gear @ 6500rpms with a 1.88:1 second gear and 3.55 rear gears with a 25.7" tire. All of that is theoretical using the Wallace racing online calculator. Rims are based on 2006 z06 18x9 fronts and Toyo R888 275/35R18 tires. Transmission ratio is from the TKO600RR. I would like to use a 5spd transmission and stay around the 3.5:1 range for the rear. So the road race TKO and relatively mild rear gears archives the 70-75 mph in 2nd gear rule.

Same calculator, same tire diameter, same rear gear ratio, same 6500rpms, just changed to the .84:1 OD gear of the TKO600RR, and this predicts a top speed of 166mph. I think that will do just fine.

[Flash68]

While the 434" engines made the most power ... torque & horsepower ... they were too hard to drive fast. With 4" of stroke, the drivers were always struggling to get them off the corner optimally. They had to drive them with the proverbial egg under the throttle. That's doable occasionally ... but not consistently lap after lap when your adrenaline is up. The 355"-377" engines had way less tire spin challenges ... but just didn't make enough torque to accelerate the car off the corner optimally. The 383"/388" engines came of the corners hard, but laid over on the straights.



That's funny Ron. I started with a 377 and quickly discovered that was a big issue on both AutoX and road course. So, I decided to go overboard and skip all steps in between and go with a the big bore big 4" stroke 437"! :lol:


The engines that were "just right" were big bore (4.125"-4.185") & medium stroke (3.750-ish). These 400"-410" engines were dominant.


So, what you're saying is.... Sprint Car engines FTW. :thumbsup:

I really wanted to go with a 3.8ish stroke but decided to reuse all the parts with my used SB2.2 "deal" I found... smart? Maybe not... fun? Should be!

I have a Camaro with a 454 cube LS7, and it never lugs out of corners versus my Coyote powered Mustang. However, put the two cars on a road course, and the less powerful Coyote motor is way more fun, despite being slower, simply because you can put your foot down and hold on almost all the time.

You shoulda bought a Miata like that Weld guy.



Maybe I am just retarded. But I'm under the impression that using a 4" stroke crankshaft will in no way limit my useable rpms.



For 99% of what are people are doing around here, I would have to agree with you.



Everyone always says that they want a broad powerband, and yet it seems no attention is ever paid to broadening it to the left. People go through great lengths to expand the powerband to the right, ever increasing the redline. And engine design and architecture reflects the chase for higher redlines with oversquare engines. Yet you can achieve roughly the same effect starting power production earlier.

3000-8500 powerband is 5500 useable rpms...

So is... 1500-7000...



A true 1500 to 7000 rpm range sounds very difficult to achieve. What would the specs of this engine look like?


Oh, and this is a winner:

Hunter S. Thompson said that men like big guns and fast cars because they push us to our limits, rather than us pushing the machine to its limits.


:bigun2: :thumbsup:

[DavidBoren]

What would a true 1500-7000 motor look like? I don't know. Hopefully it has a 3.78" bore and a 4" stroke. Lol.

But nobody knows what that motor looks like because nobody is working on extending the powerband to the left. We all know what it takes, or at least have an idea of what the motor with the 3000-8500 powerband looks like... if I had to take a guess, I would say it is probably oversquare.

[Sieg]

A true 1500 to 7000 rpm range sounds very difficult to achieve. What would the specs of this engine look like?

Something like this.........

http://g.foolcdn.com/editorial/images/96938/tesla-model-s-base_large.jpg

....but you start at zero RPM.

[mikels]

What would a true 1500-7000 motor look like? I don't know. Hopefully it has a 3.78" bore and a 4" stroke. Lol.

But nobody knows what that motor looks like because nobody is working on extending the powerband to the left. We all know what it takes, or at least have an idea of what the motor with the 3000-8500 powerband looks like... if I had to take a guess, I would say it is probably oversquare.

It looks like this:

4.130 bore x 4 stroke
Rev limit @ 7500
Torque is nearly adequate - anywhere

Spent a lot of time optimizing combination for overall powerband.

Dave

[mikels]

The other primary design criteria is DRIVEABILITY!

There are changes that could be made that would further increase power - to the right - but adversely affect driveability, so just not worth it.

Keep in mind this combination is what Mark Stielow runs in his cars, and is able to autocross in 1st gear (3.25 FDR) with precise control.

Combined with 700 rpm idle, pump-gas operation, no sags or other compromises in operation makes this a nearly perfect all-around package.

Dave

[DavidBoren]

That is a very sexy motor. And although impressive, it is more than I personally need. I also have some tingling fear of boosted LS7 blocks. No real reason. Haven't even heard that many horror stories about too much boost grenading the block. I just personally wouldn't do it. Note also, that I chose the small bore block specifically for its thicker cylinder sleeves. From what I understand, the LS7 has such thin sleeves that not even GM would put boost to it, and GM put a turbo on 4.3L V6. Lol.

Sweet engine though. Very impressive curve. Thank you for sharing this.

[mikels]

That is a very sexy motor. And although impressive, it is more than I personally need. I also have some tingling fear of boosted LS7 blocks. No real reason. Haven't even heard that many horror stories about too much boost grenading the block. I just personally wouldn't do it. Note also, that I chose the small bore block specifically for its thicker cylinder sleeves. From what I understand, the LS7 has such thin sleeves that not even GM would put boost to it, and GM put a turbo on 4.3L V6. Lol.

Sweet engine though. Very impressive curve. Thank you for sharing this.

We've not broke one yet (with ~30 of them running around now starting in 2008). And our guinea pig Mark is not known for driving his cars gently......

The advantage of making really big power is you just can't make it for very long - run out of real estate.

Don't get me wrong, this combination would likely never pass GM's GED (Global Engine Durability) test - that and a 100K mile powertrain warranty prevent factory from ever offering this.

Key is optimized design with combination of high-quality parts and precision machining & assembly. These engines will be very unforgiving for carelessness.

Dave

[DavidBoren]

Relating back to what Hunter Thompson said about big guns and fast cars... These sorts of machines are not intended for the careless.

I am sure that the LS7 blocks hold up fine... All 30 of yours seem to be working. But I am my father's son. And we have a tendency to over-engineer things. We choose our mechanicals based on its ability to survive the apocalypse.

We aren't afraid of maintenance, nor do we shy away from or skimp on routine maintenance. But we prefer machines that can persevere and last. I understand that the parts you select will be a huge factor in long-term reliability, with the single biggest contribution to durability being the quality of prep and assembly.

Because we all know that if it's sloppily put together with poor tolerances, then even the best parts will not be reliable. And likewise, if you take your time and blueprint/ balance even mediocre components and assemble them to the proper tolerances, then you will have a damn dependable motor.

My grandpa won't ever own a motor with an aluminum block. He doesn't trust it. He also won't own a rifle he doesn't trust to work as a club, either. Ask him what he thinks about the M-16, or import cars for that matter (he views both with equal disdain). Lol.

Anyways, for my particular tastes and needs, I want an engine I can rely on and put some real miles through. And I don't need 7.0L for what I'm doing. If an undersquare 359" doesn't do what I expect/ want/ need, I will boost it (like everyone else who doesn't know how to make horsepower like a real man... another piece of wisdom from my grandpa).

As for the reliability issues associated with undersquare architecture, I think I can handle the increased heat load with a more efficient cooling system (larger radiator/ fan, oil cooler and oil squirters, etc). And high quality parts with a damn proper fit and balance should handle everything else.

[Twoblackmarks...]

What is your plan?

1#Do you know what your max RPM will be, or you want it to be?

2#And what max power you want? This could impact max RPM of course.

3#And is it gonna be a carb type intake or injection?

Intake runner length could maybe be an issue to get OPTIMAL, if you are gonna run low RPM and carburetor?

ITBs could maybe flatten out your power curve.

But why not just have a "really big" engine with a small cam, and small runner heads, then you can have that flat power curve in a low RPM?

In my opinion I dont see any problem with an longer stroke than bore, my short deck 1.8Litre VW has 3.18bore 3.40 stroke and short 5.66 rods and makes peak HP at 6100. The stock 2 litre has 3.65 stroke I think. But if the bore gets to small compared to the stroke/total engine size, I would think the valve shrouding or size would limit the power potential. Especially in a 2 Valver.

If you increase the bore too, you would get even more bottom end, and probably more everywhere, so why not more bore too?

(This is like an modern 305 vs 350 discussion, the 305 too has 3.78 bore) I have nothing against 305s though, I like difference.

[DavidBoren]

I am far from building this, I'm really trying to get as much information as I can before I commit to any one thing or another. I figure with the proper amount of research and preparation, I should be able to minimize scope creep during the building phase.

But I don't have any power goals. I'm not chasing numbers. I am studying the different designs of engine architecture and I want to test something out.

The LS motors are the obvious starting point, given that parts interchange so easily and just about any combination of square, oversquare, or undersquare can be achieved using basically stock parts.

My general rule of thumb is that a vehicle should have at least one ft/lb of torque for every ten pounds of race weight. That's all vehicles. For spirited driving/hooning, a daily driven weekend track car should have at least one ft/lb of torque for every 7.5 pounds of race weight. And a track only car should have at least one ft/lb of torque for every five pounds of race weight. Peak horsepower means absolutely nothing to me, as long as it's high enough to get me the torque I want.

Those are arbitrary ratios that I made up some time ago. To me, it makes sense, and it keeps the power goals in proportion to the vehicle. The 4500#, 10 second Hellcat is a 1ft/lb of torque to 7.5# of race weight vehicle, just for reference.

I don't really have power goals outside of making sure my truck can scoot. If the engine I build, by the design I choose, doesn't perform how I want it to, I will do what everyone who fails at building an N/A motor does... boost it.

[DavidBoren]

My plan is to definitely use fuel injection. Probably just a LS2 intake for starters. But I am open to change it to optimize my powerband, for sure.

No horsepower or redline goals, as long as they're high enough to get me the torque I want.

Inch for inch, I think my undersquare six liter motor will be better than the stock 6.0L out of a truck, because the longer stroke should help power come on earlier (juxtaposed with the 3.6 crank), and I will have a higher redline. So, compared to the stock six liter LS, I should see my torque earlier, AND make power higher into the rpm range... with the proper cam, of course.

Even using a stock six liter cam and stock six liter tune, the 4" crank should give a noticeably broader and flatter powerband just because the torque should be showing up earlier, all other things being equal.

Note, I will be using heads ported to flow AT LEAST as well as stock six liter heads. So in a 6.0 vs 6.0 shootout, even if head flow, cam, intake, injectors, and tune are all the same, the only difference being undersquare vs oversquare... My undersquare motor SHOULD have a better (being broader and flatter) powerband with the same top end. If my heads flow the same, despite the smaller valves, and if the 4" crank doesn't lower the redline, then I will lose nothing up top compared to the stock (oversquare) engine. Yet I should gain a noticeable improvement down low.

[DavidBoren]

I do have a question about optimizing induction to compliment engine design.

Do you play to the design's strengths, or use the induction system to make up for weakness

With a stroker motor, you should have all the low end grunt you need as an inherent feature of the design, so do you put a single plane long runner intake on it to help improve the top end, or a dual plane short runner intake to further compliment the low end torque?

Same with adding boost. Do you put a turbo on a high revving short stroke engine to use those extra rpms? Or do you put a positive displacement blower on it to make up for the short throw and add some bottom end?

Or, in the case of my proposed undersquare 359" engine, would a dual plane rpm air gap intake be best to really compliment that 4" crank, and get as much low end as I can... Or do I throw a single plane victor jr intake on it to try get a little more up top? Same question about boost. Trust that the long stroke will provide all the low end I need, and put a turbo to give me some top end? Or just throw a blower on it and have all the low end torque ever?

I suppose it will depend greatly on my intentions. However, I find it very hard to believe that I will require anything extraordinary in terms of the redline for this motor. The supercharged LSA has a 6200rpm redline, the LS7 has a 7k redline, so I will split the difference and establish a theoretical 6600rpm redline for the sake of this discussion. My calculations from the other page put a projected top speed of 166mph @ 6500rpms, which I am okay with.

Any thoughts on induction versus architecture in general? Or in relation to my proposed undersquare six liter?

[mikels]

My plan is to definitely use fuel injection. Probably just a LS2 intake for starters. But I am open to change it to optimize my powerband, for sure.

No horsepower or redline goals, as long as they're high enough to get me the torque I want.

Inch for inch, I think my undersquare six liter motor will be better than the stock 6.0L out of a truck, because the longer stroke should help power come on earlier (juxtaposed with the 3.6 crank), and I will have a higher redline. So, compared to the stock six liter LS, I should see my torque earlier, AND make power higher into the rpm range... with the proper cam, of course.

Even using a stock six liter cam and stock six liter tune, the 4" crank should give a noticeably broader and flatter powerband just because the torque should be showing up earlier, all other things being equal.

Note, I will be using heads ported to flow AT LEAST as well as stock six liter heads. So in a 6.0 vs 6.0 shootout, even if head flow, cam, intake, injectors, and tune are all the same, the only difference being undersquare vs oversquare... My undersquare motor SHOULD have a better (being broader and flatter) powerband with the same top end. If my heads flow the same, despite the smaller valves, and if the 4" crank doesn't lower the redline, then I will lose nothing up top compared to the stock (oversquare) engine. Yet I should gain a noticeable improvement down low.

I do have a question about optimizing induction to compliment engine design.

Do you play to the design's strengths, or use the induction system to make up for weakness

With a stroker motor, you should have all the low end grunt you need as an inherent feature of the design, so do you put a single plane long runner intake on it to help improve the top end, or a dual plane short runner intake to further compliment the low end torque?

Same with adding boost. Do you put a turbo on a high revving short stroke engine to use those extra rpms? Or do you put a positive displacement blower on it to make up for the short throw and add some bottom end?

Or, in the case of my proposed undersquare 359" engine, would a dual plane rpm air gap intake be best to really compliment that 4" crank, and get as much low end as I can... Or do I throw a single plane victor jr intake on it to try get a little more up top? Same question about boost. Trust that the long stroke will provide all the low end I need, and put a turbo to give me some top end? Or just throw a blower on it and have all the low end torque ever?

I suppose it will depend greatly on my intentions. However, I find it very hard to believe that I will require anything extraordinary in terms of the redline for this motor. The supercharged LSA has a 6200rpm redline, the LS7 has a 7k redline, so I will split the difference and establish a theoretical 6600rpm redline for the sake of this discussion. My calculations from the other page put a projected top speed of 166mph @ 6500rpms, which I am okay with.

Any thoughts on induction versus architecture in general? Or in relation to my proposed undersquare six liter?

Just a few thoughts from your comments:

-LS6 intake is superior to LS2 for cathedral port heads. Difference is how they are made (LS6 keeps intake runners isolated from one another entire length, LS2 has small air-gap between upper & lower runner halves.

-Dual plane intake purpose is to increase vacuum signal to carburator. If injected, no reason to use (actually reasons not to use).

-Proper component selection will likely result in nearly identical power bands from either 6.0L combination. If limiting factor is head flow (even with larger bore), not much difference. Longer stroke means more dwell time (and therefore knock sensitivity) - so if running pump-gas, likelyhood of generating substantially more torque with longer stroke is reduced.

-Displacement will win over bore/stroke combination for peak power and bandwidth. 4" stroke 6.0L is 408" motor (if I recall correctly). Issue with 4" stroke on everything short of LS7 is bore depth - 4" stroke will pull piston pin slightly out of bottom of bore at BDC - not so great for piston stability.

-Either combination could turn to 7-7500 with right internals. Need to turn to 7-7500 is dependent on cam, heads, etc.

-'Build' the combinations in Dynomation or other capable modeling software and compare. Program is much less expensive than parts (and can infinite number of combinations for free).

-Many people forget that the engine is a 'system' and neglect to select proper combination of parts for optimization.

-Assuming you have a 'limit' to your budget, you will be restricted at absolute optimization of all components. Again, that's why suggestion of running math models prior to parts purchase to see what is best 'bang-for-buck'.

-Forced induction requires same attention to detail as N/A. Either turbo or supercharged you need to look at everything and balance package for your intended usage.

-I always focus on breadth of powerband - and if for street use, who cares if you give up 20-50hp at top end to improve bottom end. You spend very little time at high revs (even on an aggressively driven street car). Example: We changed cam's in a build we did for friend of mine (built LS7). Gave up ~50 hp @ 7200 rpm for a gain of 100 #/ft @ 2000. SO MUCH better overall package for his street driven (occasionally track, autocross) car.

-Glad to read you are not 'chasing the internet pissing contest of peak HP' - that's a sure way to end up with a pathetic combination that is miserable to live with on daily basis.

-One last note: The power curve I posted earlier was the result of 6 years of continuous optimization of our 7.0 SC package. 1st version made 780hp/830tq. Now @ 1010hp/1020tq. But devil is in the details - and takes time (and money!!) to ferret those out.

Dave

[clill]

I have no mo money !!!!

[mikels]

I have no mo money !!!!

Bummer..... Then how are we going to do the 1 MW engine for you?

Dave

[DavidBoren]

Wow, once again I get surprised by how little I actually know. I honestly didn't know that dual plane intakes have no use on a efi motor. Man, I don't know ****.

And that's why I'm here posing these questions. The TEA stage two ported 5.3 heads flow to 320 @ .600, so that would be my ultimate determining factor. The heads support six liters of displacement up to 8k rpms with those numbers, according to the Wallace racing online calculator.

I'm not building a racecar, to tell the truth. It's a 1982 2wd S10. I wanted to see what the lowest displacement motor I could build with the longest OEM stroke available in the LS platform. I actually chose to build the smallest 4" crank LS possible, on purpose.

This will be my first time completely building an engine, as I'd you can't tell. So I chose to build it small. With a displacement handicap, as I learn more and develop more as a driver... If I outgrow what the 3.78 bore is capable of providing, then I will build a new, obviously larger, motor utilizing everything I have learned.

For now, given that the only 4" stroke kit for the 3.78" bore is all forged, and how easily boost can be added, even with the 10:1 compression ratio the wiseco pistons have, I am sure I could get more than enough power to kill myself in a 3000# truck, even out of a small bore six liter.

So I will probably be playing with this combination for a while. Hopefully I can get something half as respectable as yours in the next decade or so.

[DavidBoren]

Also, I am getting conflicting information regarding possible knock issues.

Everything I read, up to this point, says that the long rods inherent to a long stroke will slow the piston near top dead center. This will provide the increased dwell time at TDC, as you stated.

But I read that decreases the risk of detonation, so I would appreciate some clarification, please.

Does the piston slowing down near TDC simply increase the amount of time it is possible for detonation to occur? Or does something about the piston slowing down actually cause or invite detonation to occur?

My understanding of it, from what I have read, and how it was explained to me, is that the reduced rate of compression decreases the likelihood of detonation. Am I wrong?

I can see detonation issues being inherent to the small bore size, as we discussed earlier... Less surface area to dissipate heat into the cooling system. More latent heat in the engine raises the risk of detonation.

It could be argued that I will see no benefits of what long conrods can provide because my 4" stroke gives me a 1.53:1 rod ratio, which isn't great. So my rod angles are still relatively severe, so I probably won't see any decrease in piston speed near top dead center. If anything, it may act like a short rod motor and increase in speed at TDC.

If it has more to do with the rod ratio than the actual length of the rod, then I probably won't see any increase in dwell at top dead center. And therefore, I probably won't have the detonation issues you warn of.

However, I am still in need of some clarification on this.

Does increasing dwell CAUSE detonation, or simply increase the amount of time it may occur?

When discussing piston speed, does the actual length of the rod matter? Or is it all about the ratio in comparison to the stroke? The change in rod angle determines the relative change in speed, and the ratio is constant in the sense that any length of rod with the same ratio will change the same relative angle, right? So any length of rod with a 1.53:1 ratio will give you the same relative change in speed near top dead center... Correct?

If that's the case, then my stroker is actually more of a short rod motor, because 1.53:1 is kind of low.

[cjsgarage]

David,
I'm struggling to remember everything I've learned (especially just recently) and am no expert by far. But I have taken a few classes from experts and read more than one book on the subject. THANK YOU for starting this thread. It's cool to have insight from giants like Ron Sutton and all the other well-learned ones on this forum.

anywho. One of the points I actually can remember from my last class: High Performance Engine Design and Theory from Allen Osborne was that, the bigger bore always seem to make the better power. And I understand your desire to move the powerband down the RPM range.. but there's a reason NHRA and others are up to 4.7 bores. Something about shrouding the valves.

The other point I remember him saying was, to use the longest rod possible. Not necessarily as a stroker.. he meant pushing the rod up into the piston as far as you can--getting a wrist pin as close to the piston head as possible.

I looked for my notes on the class, but they escape me for the moment.



anyway. What about building the more common over-square engine with camshaft designed to pull the power band a little lower? Just a devil's advocate kind of thing.

It seems like you're pretty set on what you want to do, build the 3.78x4 engine. Maybe you'll have enough parts to build a second one if you use all OEM parts, and you can try oversquare similar displacement as you mentioned on page 1.
I do think Dynomation5 would serve you well at this point. It's made by Motion Software.



More food for thought: This is something I found on another forum:
Where B = bore, S = stroke, N = number of cylinders, and C = a constant for fuel quality, materials, stress levels, etc.:

HP ~ B^1.65 × S^.5 × N × C
(after F. W. Lanchester)

Removing N, most power by far, is big bore + short stroke

[cjsgarage]

Also, I am getting conflicting information regarding possible knock issues.

Everything I read, up to this point, says that the long rods inherent to a long stroke will slow the piston near top dead center. This will provide the increased dwell time at TDC, as you stated.

But I read that decreases the risk of detonation, so I would appreciate some clarification, please.

Does the piston slowing down near TDC simply increase the amount of time it is possible for detonation to occur? Or does something about the piston slowing down actually cause or invite detonation to occur?

My understanding of it, from what I have read, and how it was explained to me, is that the reduced rate of compression decreases the likelihood of detonation. Am I wrong?

I can see detonation issues being inherent to the small bore size, as we discussed earlier... Less surface area to dissipate heat into the cooling system. More latent heat in the engine raises the risk of detonation.

It could be argued that I will see no benefits of what long conrods can provide because my 4" stroke gives me a 1.53:1 rod ratio, which isn't great. So my rod angles are still relatively severe, so I probably won't see any decrease in piston speed near top dead center. If anything, it may act like a short rod motor and increase in speed at TDC.

If it has more to do with the rod ratio than the actual length of the rod, then I probably won't see any increase in dwell at top dead center. And therefore, I probably won't have the detonation issues you warn of.

However, I am still in need of some clarification on this.

Does increasing dwell CAUSE detonation, or simply increase the amount of time it may occur?

When discussing piston speed, does the actual length of the rod matter? Or is it all about the ratio in comparison to the stroke? The change in rod angle determines the relative change in speed, and the ratio is constant in the sense that any length of rod with the same ratio will change the same relative angle, right? So any length of rod with a 1.53:1 ratio will give you the same relative change in speed near top dead center... Correct?

If that's the case, then my stroker is actually more of a short rod motor, because 1.53:1 is kind of low.

There's trade off between lower thermal efficiency/increased quench and piston speed decrease. Less heat dissipation leaves room for detonation. Piston speed decrease theoretically dispells detonation. And there's theorectically power loss from increased quench (remember our cast iron head bit?)

I don't really think it's a big deal. If you stay Fuel Injected, that's very very tunable. I have timing control for Cylinder Mass every .02 g/cyl or something crazy like that.

Length of Rod and Length of Crank matter for piston speed. But keep in mind, your highest piston velocity is going to be with the crank and rod are at a 90* angle.

You are correct in saying rod ratios correspond to piston speed.

None of it is terribly important. Good tuning can get rid of pretty much all detonation in Fuel Injection. Knock sensors pretty much take care of pitting pistons/breaking ring lands nowadays.

some good reading for you
http://www.contactmagazine.com/Issue54/EngineBasics.html

[DavidBoren]

See, the dumb mechanics of it are actually what is important to me.

I understand that tuning can make up for deficiencies. I understand that tuning can make the torque hit early in a short stroke, big bore motor.

I want the parts involved, the ratios, the entire design and architecture to reflect what the engine us built for. You can look at a T-rex skeleton and know it belonged to a carnivorous critter. All it is is a set of jaws with some legs. Without cam cards or timing tables, I want you to see exactly what the motor is good at, just based on design.

I want what it is physically, all the ratios and geometry of its design, to reflect what it does or excels at. I don't want to tune an engine built one way to operate differently.

I want to build MY engine. Based on what makes sense to me. If it doesn't work, if what makes sense to me fails, then I will start over, with some new knowledge and experience to help improve the next one.

It's not a test of any particular principle or another, it's more just to see if what I think SHOULD work actually does. If it does, great, being right is awesome. If it doesn't work, great, learning to do something right is awesome.

It's more about the journey than the destination for this first engine build.

Regardless, it's all but impossible for me to screw this up. I am going to end up with an LS motor with the same, or better, displacement, redline, and head flow as the LS2. And nobody questions how potent that 364" small block is.

[cjsgarage]

David,
I just meant to say that the detonation is a non-issue with a good tune. It's not like you're building a 14:1 engine. You should be able to run pump gas and not have detonation.. as long as the tune is set up.

I look forward to seeing your engine come together.

[DavidBoren]

So, I'm pretty sold on the idea of running oil squirters and an LS9 (or similar) oil pump. But in researching oil squirters, I got to thinking, which can be dangerous for someone who doesn't know much.

Now, in relation to increased stroke causing an increase in heat/ friction...

Would the decreased circumference of a smaller bore translate into less friction (heat) being generated for the same stroke with a larger diameter bore/ piston?

We discussed the decreased surface area of the smaller bore being less efficient at transferring heat to the cooling system, and we talked about how increasing stroke will generate more heat. But it was never covered if increasing bore diameter has comparable increase in friction heat.

An undersquare motor would have smaller pistons, think smaller piston ring surface area, traveling a longer distance.

An oversquare engine would have more piston ring surface area traveling a shorter distance.

With both engines in question being of equal displacement, both spinning to the same redline, does one really generate more or less heat than the other?

Does less surface area traveling further generate more friction than more surface area traveling less?

More specifically, would MY proposed undersquare six liter, with its 3.78" bore and 4" stroke, generate LESS friction heat than, say, the LS2 with its 4.00" bore and a shorter 3.6" stroke? The 4.00" pistons have almost four more square inches of surface area interacting with the cylinder walls!

Using a relatively generic 1.2mm, 1.5mm, and 2.5mm ring set for both, the 3.78" piston has 61.78 square inches of surface interaction, per piston. The 4" bore piston, with the same ring set, has 65.36 square inches of piston ring surface, per piston.

Math:
3.78" x 25.4 = 96.01mm
Pi x 96.01mm = 301.63mm
301.63mm x (1.2mm + 1.5mm + 2.5mm) = 1568.48sq/mm
1568.48sq/mm / 25.4 = 61.78sq/in

[Twoblackmarks...]

I am no expert at all on this. But I do think you are overthinking this somewhat.

My thought is like this.

The piston rings I would think not making much more heat, modern low tension rings are not "springed" up to the cyl. wall. They are for the most part only under "tension" in the compression cycle.

And stroke, together with bearing size, I would think produce much more heat than anything else, because the piston speed is higher and the piston travels longer.

Since you say you would like a torquey engine, I would think your intake runner length, head size and camshaft choice has a much bigger impact on your engine than anything else.

Oldsmobiles and Buicks are known for their torque, I do not think that is (only) because of the stroke, but because of their wide intakes they got much longer intake runners than other brands. This is just my opinion though, not based on proof and facts. But to me it seems sensible.

All small block Olds` have an 3.385 stroke, they also produce good torque, because of the long intake runners.

And with a not so long stroke it is easier to have a better rod length without putting the pin up to high in the piston, I would think this creates a much smoother running engine, with a more stable piston. That runs smoother and quieter than an long stroke more "stressed" engine.

A lot of people who build stroker BMW engines, to fit the longer stroke they must put in a shorter Rod, that works fine, even though I think it is somewhat going the wrong way, they still make more power, because the engine is still bigger than it was before. There is no replacement for displacement any way how you choose to make it bigger.

[DavidBoren]

Thank you for your response.

It has been brought up before that intake runner length and cam selection would have a more noticeable effect on torque production. And I am sure that they do.

But increasing mechanical leverage has to produce a noticeable difference. It has to. All other things being equal, if you had a LS2, a L99, and my proposed undersquare six liter... The intake and cam difference between the L99 and LS2 should demonstrate what everyone has brought up.

I am hoping that I can achieve that same difference with just the mechanics of how my proposed engine is assembled. Whatever makes the truck engine a L99 and not just another LS2, the change in the powerband that makes the L99 haul hay, while the LS2 hauls ass, that extra something down low that makes the L99 a truck motor... I'm hoping that I can achieve this same extra something down low through nothing but additional mechanical leverage.

For the sake of this discussion, we will say that I will put a LS2 cam, LS2 intake, LS2 throttle body, LS2 injectors, and a standard LS2 tune on my proposed undersquare six liter motor. It is essentially an undersquare LS2. At this point, the ONLY things different are the bore to stroke ratio, and head flow. Since I have been talking about using TEA's stage two ported heads, they outflow stock LS2 heads. So, please assume that the LS2 heads have been touched up to flow [email protected] as well.

Anyways, I build an undersquare LS2, right. All things being equal (tune, cam, intake, injectors, etc), what changes do you think the 4" crank would, or should, bring?

If the heads flow the same, using the same injectors and intake, same tune, same cam, same exhaust. All things being equal, except for the only difference being a 359ci undersquare longblock versus a stock 364ci LS2 longblock, do you think that there would be a noticeable difference between the two?

If it does give me something extra down low, awesome. I think it should.

If it doesn't, oh well, I have a forged six liter V8 that's a proven platform for boost... I think I will be ok.

But I do think that I can achieve this truck motor something extra down low, without sacrificing anything at all up top. If I choose parts that can withstand the abuse, and I am willing to spin the 4" crank as fast as GM spins the LS2, and my heads flow equal to or greater than the LS2, then I will be able to push the same cam/ intake/ injectors/ blah blah blah just as high as the LS2... But I will have the added mechanical leverage of the 4" stroke, if that proves to be beneficial or even measurable.

Thoughts?

[Twoblackmarks...]

My opinion:
IF it would fit I would think that you loose power everywhere, except maybe under 2K RPM maybe.

I checked those heads and they have 2.04 & 1.57 valves = 3.61" I dont think they would fit in a 3.78 bore, and IF they fit you would loose a lot of flow because of shrouding.

And they probably also have an combustion chamber that is bigger than 3.78 so they will get "overhang" and probably gasket problems.

And the .600 flow number does not matter since the cam only have .525 lift, and the mid range lift flow numbers are much more important than the peak lift/flow number anyway.

I see that all LS engines (and modern engines actually) have pretty big runners (compared to older engines SBC etc), but I would think that a 229cc runner does not promote a good low RPM torque engine. Even though it is modern tech. I dont know how small LS heads you can get, but I would think that you should not go over 200cc if you really want a torquey engine. You must match your heads to the rest of the engine.

EDIT: I think there is a page called Speedtalk? There there is a lot of knowledgable engine people I think, maybe they have some input.

[DavidBoren]

Can you please explain why you think that my proposed undersquare 359" six liter motor would be worse than a 364" oversquare six liter motor, when all things are equal other than architecture?

Surely 5ci of displacement isn't going to be noticeable. And if everything else is the same, from the air filter to the rear tires... The ONLY difference is the LS2 achieves its 364 cubic inches with an oversquare bore/ stroke ratio, and "my" engine gets its 359 cubic inches via undersquare architecture.

Why do you feel that the undersquare architecture would be a detriment across the board? I'm pretty sure that the 5.3 and the LS2 both have heads based on the same casting. So if head flow is equal. Displacement is equal. And redlines are equal. Same accessories. Same cam. Why would "my" engine lose power everywhere?

If anything, worst case scenario, wouldn't it just be the same as a LS2? Why and how would I possibly make it worse?

What, exactly, are you referring to when you say "if it will fit"?

If you are referring to the intake valve size, yes, a 2.04" intake valve will fit. Yes, it will be shrouded in the 3.78" bore. Will ported 5.3 heads outflow, or AT LEAST flow as well as, stock LS2 heads even with shrouded valves? Yes.

I don't have to get the stage two porting. For the same price as TEA's porting services, I can get some trick flow heads. And they are meant for the 5.3L, or at least made for the 3.78" bore, and they have 2" intake valves.

No matter what, I can get at least as much air flow as stock LS2 heads. Given that the 5.3 is a truck motor, I'm guessing that GM already has done what needs to be done to make the 5.3 heads flow for best truck-like torquey performance.

Am I absolutely missing something? The way I see it is that it is fairly impossible for me to mess this up. "Failure" for this project is 400hp and 400ft/lb of torque. That's what LS2 parts on a six liter air pump produces.

Air flow determines redline. Redline determines cam. Cam determines how your engine uses the air flow up to the redline. Right?

So if I have a six liter motor with enough head flow to support the same redline as the LS2, and I am using the same cam, then at the very least I should expect to see the same result at redline... Regardless of whether the air pump is over or under square.

Now, I personally think that I will actually see an increase, everywhere. Let's say that the added mechanical leverage provided by the 4" stroke only adds 25ft/lb of torque, 500rpms sooner. Everything past that point will be higher than the same rpms on a LS2. Why?

Horsepower is a function of torque. Increasing mechanical leverage to increase torque will inherently increase horsepower with it.

Let's say that the LS2 cam is capable of climbing five stairs. In the stock application and configuration, the last step is at 400hp and 400ft/lb of torque.

But my 4" crank six liter motor gave us 25ft/lb extra, so the same cam climbing the same number of stairs reaches 425...

Assuming you can follow my analogy comparing useable powerband to a flight of stairs.

After all, an engine is nothing but an air pump. The fact that we choose to add fuel to and then burn the air, as we pump it, does not change the fact that an engine's primary function is to move air.

The amount of air the pump can move determines how much fuel can be added. Things like compression ratios and the timing of ignition events all determine how much power that amount of fuel, in that amount of air, can or will produce.

However, you can change how that power is transmitted from the pump to the ground. Things like mechanical leverage are dumb. Dumb in the sense that mechanical leverage exists without any air being pumped. Increasing the length of a lever increases torque. The end.

So, all other things being equal, increasing the stroke from 3.6" to 4" has to produce an increase in torque... Does it not?

And if you increase torque anywhere, any earlier, then all numbers after that point will be higher, because horsepower is a function of torque. So if you take it to the same redline, then theoretically, there's no way for the end result to be lower.

[Twoblackmarks...]

This is only speculation from my side. If you had 4" bore vs 4.3" bore it would be much more equal I think, over 300cid should not have less than 4" bore to get a big enough valve to feed all the cubes, if big power is goal!

If the valve is very close to the cyl wall, you not only get less flow, but it may restrict the amount of lift you can make before the valve hits the cyl wall.

But I dont know anything about that, you must try and test. But if you cant open the valve more than say .400 before it hits the wall. It would not exactly increase performance.

A shrouded big valve probably flows less than an small un shrouded valve, and the shrouded valve makes poor swirl since everything "chrashes". Unless maybe the wall for some reason increases swirl, who knows?

But it does matter what valve angles and center placement it has. And not forget about how the "TEA" combustion chamber diameter fits to gasket and bore.

With an head that fits well on both engines it may not loose as much power, but if you take advantage of the bigger bore on the big bore engine, that one will probably make best overall power, and more total.

How much power do you want? 350 or 450, 600 or 800?

I can try to make an graph in Engine Analyzer where I change nothing but Bore and Stroke and leave everything else equal. To make an comparison if you want.

Big bore = More Flow = More Power. Add a long stroke to that and it is win win!

[DavidBoren]

Ok. I see where you are coming from. For most, the pursuit of large horsepower numbers trumps everything else.

I am not amongst this crowd.

I have no real need or overwhelming desire to necessarily best the performance of the LS2. A streetable 400ft/lb motor is more than adequate for my ambitions.

I would like for my particular design to outperform the LS2 based solely on pride, because I would forever convince myself that I am smarter than GM's engineering team. But I don't NEED more than what a bone stock LS2 has to offer.

I chose the smallest possible displacement using stock GM bore and stroke options that still allowed me to use the 4" crank. I chose the smallest bore diameter GM offers, on purpose, to test something that I think SHOULD work.

After choosing the small bore block and 4" stroke, I saw that made six liters of displacement. In finding out that my chosen combination was just five measly cubic inches from the LS2, I then decided to use it (the LS2) as my base for comparison.

I found that the LS7's redline is higher than the LS2, so I can still match or exceed the LS2's redline using a LS7 crank. No worries there.

I found that I can have the 5.3 heads ported to match or exceed the flow of the LS2 heads. So no worries there, either.

If my proposed undersquare configuration does prove to be better than the LS2, cool. Yay me.

If it doesn't. Then oh well, I am left with a stroked 5.3L, making it six liters, with a forged rotating assembly, and ported heads. That's not too bad for a "failed" project.

In fact, that is the beginnings of a wonderful boosted motor success story.

I know that I have been preaching about all things being equal, but they aren't going to be. I am going to use a more aggressive cam than the LS2 has. It is the most aggressive vvt cam from comp cams. Oh yeah, my undersquare six liter motor is going to have variable valve timing. My redline will actually be higher than the LS2. My heads will flow more than the stock LS2 heads. Given that displacement and compression are equal, but my engine having a better cam (with vvt), better head flow, AND a higher redline... It is literally impossible for me to not match or exceed the performance of the LS2.

[Twoblackmarks...]

I am not a high HP chaser.

Does the LS7 crank fit in a normal LS block?

It is more than an crankshaft that selects your redline.

[DavidBoren]

Crankshafts have nothing to do with redline if we are only referring to the stroke of a crankshaft. With light enough, more specifically less massive, moving parts, stroke plays absolutely no limits on redline. The only limiting factor is heat through friction and vibration issues caused by large amounts of mass spinning really fast. Natural frequencies and the efficiency of the cooling system play a larger role than just the length of stroke.

I determine my redline based on cylinder head flow. I used online calculator(s) to see what the head flow numbers I had available could support. The Wallace racing online calculator said that the TEA stage two ported heads could flow enough to support six liters of displacement up to 8000rpms.

General Motors spun the LS7 to 8k during testing. So I knew the 4" crank (combined with lightweight parts) would not be an issue. Especially considering I will have smaller, less massive, pistons which is reducing weight/ mass out on the important end (so it doesn't matter as much if my non-titanium rods weigh more because that weight/ mass is closer to the axis of rotation).

Once I saw that the 5.3 heads could be ported enough to support six liters of displacement spinning at 8k, I honestly stopped worrying or even thinking about the redline.

Whatever the end of the powerband to the aggressive vvt comp cam is will be my redline. People on the interwebs talk about revving the vvt LS motors to over 6600rpms once the afm/dod is eliminated and new lifters are installed. And I'm sure +/- 6500rpms will be plenty for me.

But anyways, to answer your question, yes a 4" crank will fit in the standard block. I am not a pioneer in this effort. Wiseco makes forged pistons specifically for use with a 4" stroke and 6.125" rods in the 3.78" bore block. I believe K1 offers a complete forged rotating assembly using these pistons.

For reference:
LS2 cam is something like 204°/218° .551"/.547" 117° lsa

The aggressive vvt cam is 218°/222° .566"/.578" 114° lsa

Take whatever conclusions from that as you will. But, to me personally, it would appear that the aggressive vvt cam would favor a higher redline than the stock LS2 cam. And that's why I have stated that my redline would be higher than a stock LS2.

[DavidBoren]

Simple question, seeking a common consensus...

Do you think that a bone stock LS2 would show a NOTICEABLE difference if you swapped in my proposed undersquare long block, assuming head flow and compression were the same?

Only change being bore and stroke, 4.00 x 3.60 vs. 3.78 x 4.00...

I hadn't originally started this thread to be about this particular engine, but I have used it to keep the conversation steady, and now I feel I have presented my argument enough that I should be able to get an honest opinion of what I am trying to accomplish.

Actually, forget the LS2 comparison. I know my proposed engine will best a bone stock LS2.

What is everyone's thoughts on the use of variable valve timing?

Note for future boost:
The aggressive vvt cam from comp cams is actually very comparable to the LSA cam, hmm, positive displacement blower on a stroker motor with vvt? Talk about torque.

LSA cam: 198°/216° .480"/.480"
Comp vvt: 218°/222° .566"/.578"

Thoughts?

[mikels]

Simple question, seeking a common consensus...

Do you think that a bone stock LS2 would show a NOTICEABLE difference if you swapped in my proposed undersquare long block, assuming head flow and compression were the same?

Only change being bore and stroke, 4.00 x 3.60 vs. 3.78 x 4.00...

Actually, forget the LS2 comparison. I know my proposed engine will best a bone stock LS2.


Quick test from Dynomation simulation:

Same Cam
11:1 CR
Same Intake
CNC LS2 Heads for 1st and 2nd test (did not adjust flow numbers based on bore size - will be lower with 3.78 bore)
CNC LS3 Heads on 3rd test (note: will not fit 3.78 bore)
6.098 rod length on 3.60 stroke (stock 6.0L)
6.067 rod length on 4.00 stroke (stock 7.0L)


Typically, OEM’s don’t arbitrarily pick bore / stroke by accident. 6.0L was designed to be 4.0” bore x 3.6 stroke for a reason. As well, when 7.0L was designed (for a 4” stroke) bores were extended further into block for piston stability.

BTW, I did not spend any substantial time on this model - so although relative numbers are comparable from each test, outright numbers are not necessarily accurate.

Dave

[Che70velle]

David, the info that Dave (mikels) is posting is valuable. You can absolutely trust what he's telling you, as he does this for a living, and builds some of highest quality, time intensive, LS powerhouses in the country, with ultimate durability and big numbers. I'd be honored that he took time to run your numbers for you.

[DavidBoren]

@ dave,

I very much appreciate your response, and data. I was just thinking about the rod length earlier today, actually. I found myself wondering why wiseco made their pistons for use with a rod length other than what GM produced. And I was thinking that I would probably get pistons made so I could use the LS7 titanium rods.

Regardless, I am trying to understand the data you provided. Why does the small bore fall off? What causes it to not at least be equal? If head flow is equal, then shouldn't the power be equal? It definitely shouldn't decrease, should it? Why would the 4" stroke reduce the power, if the heads flow the same?

Is it the piston speed leaving top dead center? What causes the decrease? The 3.78" bore cylinder heads can be made to flow AT least as much as bone stock LS2 heads... Even in the 3.78" bore. So what is causing the decrease? Heat through friction? If the heads flow the same, why is the 4" stroke showing a decrease?

[Vegas69]

Large bores take better advantage of head flow.

[mikels]

@ dave,

I very much appreciate your response, and data. I was just thinking about the rod length earlier today, actually. I found myself wondering why wiseco made their pistons for use with a rod length other than what GM produced. And I was thinking that I would probably get pistons made so I could use the LS7 titanium rods.

Regardless, I am trying to understand the data you provided. Why does the small bore fall off? What causes it to not at least be equal? If head flow is equal, then shouldn't the power be equal? It definitely shouldn't decrease, should it? Why would the 4" stroke reduce the power, if the heads flow the same?

Is it the piston speed leaving top dead center? What causes the decrease? The 3.78" bore cylinder heads can be made to flow AT least as much as bone stock LS2 heads... Even in the 3.78" bore. So what is causing the decrease? Heat through friction? If the heads flow the same, why is the 4" stroke showing a decrease?

Stock rods are metric. Most aftermarket rods are standard - and pistons are made to match these rods.

Heads WILL flow less on smaller bore - valves are more shrouded by cylinder. So regardless of what you get heads to flow, they will flow more in a larger bore engine - but as I said, I did NOT change flow numbers for this comparison (which will make difference even greater than these numbers show).

So let's look at some additional differences:

While you are correct in assuming a longer lever arm will increase torque, this is only true if the cylinder pressure times surface area is the same. Say each LS2 head combination results in the same cylinder pressure. One is working on a total surface area of 12.566 in^2 (4" bore) and the other is working on a total surface area of 11.222 in^2 (3.78" bore) - or ~89% the surface area of larger bore. So to make same FORCE, will need 112% the cylinder pressure. Peak cylinder pressure occurs ~12 deg ATDC. The difference in lever arm at this crank angle for a stroke change of 0.4" is pretty damn small - certainly much less that the required 112% change in force.

Data below shows frictional losses for longer stroke are greater (no surprise). Pumping losses are slightly better for longer stroke (no surprise again). Mechanical efficiency favors the larger bore slightly. Both LS2 headed combinations flow nearly same airflow (again - I did not alter flowbench data for smaller bore). All of these are relatively small differences - up until you get to the aforementioned piston force. Now you see the primary difference between the combinations.

BTW: I do NOT believe for one second any of these combinations will make the high RPM power numbers that these simulations show. I would fully expect any of these to make peak power ~6500 rpm, and start falling rapidly after this point. If I took more time to detail the model, it would certainly reflect this.

Dave

[mikels]

David, the info that Dave (mikels) is posting is valuable. You can absolutely trust what he's telling you, as he does this for a living, and builds some of highest quality, time intensive, LS powerhouses in the country, with ultimate durability and big numbers. I'd be honored that he took time to run your numbers for you.

Thank you for the kind words and compliments!

Dave

[DavidBoren]

Thank you for the explanation. The reduction in force due to the smaller piston makes sense. I guess I was too caught up on air flow. It is really cool to see that the friction loss is negligible (below 1hp) all the way up to 4500rpms. And the mechanical efficiency is within 1% up to 7500.

And, to be honest, I was mistaken in my understanding of the physics. I was thinking that a set amount of air and fuel, with a set amount of compression and timing events, would make a set amount of force. Pressure is force divided by area, so the smaller piston with the smaller area, with the same force, would be more pressure on the crank. I guess I was approaching this from the wrong direction. So you thank you for setting me straight.

I was using a handloaders'/ ballistics approach. Same amount of powder used to push a big bullet, now pushing a smaller bullet, makes for more energy downrange. Velocity is squared in the equation for energy, so increases to the velocity trump increasing mass. I was comparing the air and fuel in the combustion chamber to the powder charge in a rifle cartridge. Pistons to bullets. And getting energy downrange to the crank.

Shows how little I know. It also shows that I am a redneck, not a physicist.

[uxojerry]

From the description of the type of performance you want, a conventional 5.3L or 6L with a custom cam would be a good bet. An engine can be cam'd for low end grunt, and peak hp at a desired redline.

A good guy to talk to is Chris Straub of Straub technologies. He does custom cam's for a lot of people.

[DavidBoren]

While a run of the mill 5.3 or 6.0 may be plenty adequate for my ambitions, it is not what I am necessarily after.

The camshaft controls the timing events that move a mechanism. And while you can custom tailor the camshaft to achieve just about any result from any mechanism, I want the actual device, the mechanism itself, to be tailored for what I want.

You can cam a normally high revving short stroke engine to produce all its torque as early as possible. Is the motor itself built or designed for low end torque, no, but you can cam it that way.

You can cam a stroker motor for top end power, too. Is it designed for high rpms, no, but you can cam it that way, if you want.

I don't really know how to explain my thought process on this. Maybe I'm just wrong or confused. Maybe it's just ego or pride, or some petty desire to be a unique and special snowflake. I don't know.

I know I care about torque more than horsepower. I know I care about what is going on in normal rpms more than what is happening in the final few revs before you burn your **** up. And I know that I have not a single care about what my peak numbers end up being.

The aggressive vvt cam from comp cams says its operating range is 2000-7100rpms. That should be just fine, and it still gives me 20 degrees of cam phasing. Which will automatically make it more streetable than any non-vvt cam, and driveability is a huge part of all this. And I can't really rev any higher than 7k rpms without going dry sump, which I am not willing to do, so there's no reason to give up vvt.

I am still going to check out Straub, it's always good to know who can make a good custom bumpstick. So thank you for passing that on.