Narrowing down my new LS engine combo..

[Steve1968LS2]

Been digging around and here's how it looks so far.

LS3 block
Darton MID sleeves
FAST Intake
either Trick Flow 235 heads or the new LS3 style AFR heads
Lunati pro-series crank
Lunati rods
Weisco pistons

Compression around 11.1:1
Bore: 4.200

Now if I go with my current 4" stroke I will have 443 cubic inches.. if I go with the next crank at 4.125 I end up 457 cubes. I'm just not sure if that stroke will interfere with the Canton F-body pan that I run to clear my rack.

The more cubes the merrier, but I trying to decide if I should just play it safer and be happy with the 443.

Thoughts?

Here's the cam I selected back when this was going to be a 427.. I might want to go bigger now.
239/247 624/624 lift on a 114 LSA

Thoughts? Looking for midrange and lowend power.

[Vegas69]

Can you get off the shelf pistons for a 4.125 stroke? If not, they are custom and substantially mo money. I was just in a similar situation......

[Steve1968LS2]

Can you get off the shelf pistons for a 4.125 stroke? If not, they are custom and substantially mo money. I was just in a similar situation......

I think you mean off the shelf pistons for a 4.200" bore?

[Vegas69]

Your piston pin height changes when you change the stroke. Unless different rods are available.

[Steve1968LS2]

Your piston pin height changes when you change the stroke. Unless different rods are available.

Yep, but I don't think it will be a problem. With the Darton deal the length of the sleeve negates some of the piston rock at BDC issues.

I'm waiting to hear back from my Wiseco guy, I will ask him about the pin height deal.

Ultimatly my bore size will be determined by what's available in terms of pistons. Darton can go up to a 4.200 and I want as much displacement as possible.

For example, I could also do a 4.125" stroke and 4.125" bore for 440 cubic inches..

[ProdigyCustoms]

Carl Wegner and I had this conversation over dinner and cocktails. The man is so smart with these things it is crazy. But I know a thing or two so I keep up pretty well.

The LS motors are , well most motors in general, but especially LS motors are sensitive to rod length to stroke ratio. Bigger is not always better. I can verify this based on a 421 Small block my body guy just built (to be bigger then my 404CI) that won't fall out of a tree. It is built identical to my 404CI with a TENNIE bit bigger cam for the slightly more cubes, but it just doesn't have the snot my 404CI motor has. And we think it is rod to stroke ratio.

With that much stroke you will need a super long rod and the pin height in the piston wont allow a good rod length and good ring package.

[Steve1968LS2]

Carl Wegner and I had this conversation over dinner and cocktails. The man is so smart with these things it is crazy. But I know a thing or two so I keep up pretty well.

The LS motors are , well most motors in general, but especially LS motors are sensitive to rod length to stroke ratio. Bigger is not always better. I can verify this based on a 421 Small block my body guy just built (to be bigger then my 404CI) that won't fall out of a tree. It is built identical to my 404CI with a TENNIE bit bigger cam for the slightly more cubes, but it just doesn't have the snot my 404CI motor has. And we think it is rod to stroke ratio.

With that much stroke you will need a super long rod and the pin height in the piston wont allow a good rod length and good ring package.

I would only be going from a 4" stroke to a 4.125" stroke.. (6.125" rod).. most of this is being made by bore size. Or if I can get the right pistons I can stay with a 4" stroke

I should probley talk with Carl.. I know enough but I'm no "expert"..

The key to this whole deal is the Darton part. This lets me have the bore of an LSX iron block with the weight of an LS2 (I think the sleeves add 9 lbs)

To be honest I'm more curious/concerned about going from 4" to 4.125" on the stroke due to oil pan/windage tray clearances.

[tobenk]

A lot of guys run the tall deck LSX block to get the rod ratio back when u start goin big cubic inches. U just run out of rod length.

[Steve1968LS2]

A lot of guys run the tall deck LSX block to get the rod ratio back when u start goin big cubic inches. U just run out of rod length.

Yea, but what is "big inches" these days?

I just built a 440 LSX (short deck) last week.. 4.125 inch stroke and bore.. Dyno on Friday, but it's very similar to this:

http://www.trickflow.com/articles/tf_440-2/

[tobenk]

I would think around 440 or 450 but when u get cubic inches with stroke u run out of room. The only place to get it with the same rod length is pin heigth. Then u start messin with piston strength.

[Steve1968LS2]

I would think around 440 or 450 but when u get cubic inches with stroke u run out of room. The only place to get it with the same rod length is pin heigth. Then u start messin with piston strength.

In this case it's mostly happening through bore size.. which normally can't happen with an LS engine to any real degree.

Original plan was a 4.125 bore and 4" stroke for a 427, but if I can get more displacement (safely) then I will.

I will know more once I talk with my piston rep.

[ProdigyCustoms]

I should probley talk with Carl.. I know enough but I'm no "expert"..

.

You should talk to him for entertainment value if nothing else. He has got some stories and has "A WAY" of puttng things that makes me laugh all the time!

[Van B]

You should talk to him for entertainment value if nothing else. He has got some stories and has "A WAY" of puttng things that makes me laugh all the time!

I can tell you stories. I spent the better part of a year with Carl and my dad at the shop when I was a kid (mid 70's) and they were working on the Pro Stock car they ran together. Carl has never been afraid to tell anyone what's on his mind... An incredibly smart man.

I seem to remember talking to Dan from Wegner's and if you go with too much stroke in these things and the piston travels too far out the bottom of the cylinder bore and rocks back and forth. I do not have a good mind for these things so I don't remember what that number was.

[Steve1968LS2]

I seem to remember talking to Dan from Wegner's and if you go with too much stroke in these things and the piston travels too far out the bottom of the cylinder bore and rocks back and forth. I do not have a good mind for these things so I don't remember what that number was.

I know.. that's why I built the 402 and not something bigger (ie, longer stroke)

piston rock at BDC is a bad thing. BUT, with the new Darton sleeves it's now really a problem since the cylinders can be made a bit longer. I'm going to try and stay with a 4" stroke, hopefully the bore size will cooperate..

[DFRESH]

Steve, what kind of RPM's will the motor be seeing---with those cam specs---looks to be around 6600 or so? Piston speed with that longer rod should be a consideration---but maybe I am still stuck in the old SBC world. I think you are right---clearance on you pan could be an issue with that size rod---didn't you have to clearance it once already for the current motor due to same issue?

[Van B]

I know.. that's why I built the 402 and not something bigger (ie, longer stroke)

piston rock at BDC is a bad thing. BUT, with the new Darton sleeves it's now really a problem since the cylinders can be made a bit longer. I'm going to try and stay with a 4" stroke, hopefully the bore size will cooperate..

I saw your post at PT about the sleeves after I had posted that. Makes sense. Like I said, my memory was sketchy.

There is no replacement for displacement...

[Steve1968LS2]

Steve, what kind of RPM's will the motor be seeing---with those cam specs---looks to be around 6600 or so? Piston speed with that longer rod should be a consideration---but maybe I am still stuck in the old SBC world. I think you are right---clearance on you pan could be an issue with that size rod---didn't you have to clearance it once already for the current motor due to same issue?

I think my peak power is around 6,300 (now) but it still makes good power even up over 6,700.

My rev limiter is set right now at 6,900.. mostly so I can hold a bit longer before shifting if I need to.

Yea, the rods slapped the stock f-bod Canton pan so we welded in a section for more clearance. That's why I want to stay with a 4" stroke and know that even adding .125 could mean more pan mods and maybe mods to the windage tray.

You can see the 402 build (and the clearance issue) in the story here:
http://www.camaroperformers.com/camaro-tech/engine/camp-0902-1968-chevy-camaro-engine-upgrade/index.html

[tobenk]

Steve i would stay with the 4" stroke then just less hassle. No pans modes
and such. I think u good use a little more tq. U said the car could take a little more power but i think torque good help u in the autocross better than horsepower. Either way both motors sound like good combos.