Re: ITB setups - benefits and drawbacks

[ArisESQ]

I searched a little but couldn't find anything relevant to my question.

Does anybody have significant experience with individual throttle body setups, particularly on LS motors?

I've toyed with the idea for a little while and have done some research on available options for relatively "turn-key" packages.... I just don't know enough about the benefits of ITB, other than they supposedly offer crisper, and sharper throttle response, and that they offer more tuneability (which could be great, or a potential nightmare to figure out).

I've looked into harrop (http://www.harrop.com.au/store/engine/ls3-7-hurricane-itb-manifold), jenvey dynamics (http://www.levelxms.com/jenvey-dynamics-chevrolet-ls3-individual-throttle-body-itb-kit), kinsler, inglese, and TWM/Borla Induction. They all vary a great deal in price, and I don't know which ones are just meant to be pretty and which ones are actually well engineered packages.

I appreciate any thoughts on this!

http://begoodphotography.smugmug.com/Automotive/holley-lsx-fest/i-d3mpmPn/0/XL/itb-ls1-lsx-XL.jpg

[Ron in SoCal]

Get ahold of Brent:

http://www.lateral-g.net/forums/member.php4?u=15112

[ArisESQ]

Thanks - sent him a PM

[PTAddict]

I have no experience with any of the above, although I've researched a lot and plan to add a Harrop system in my car in the next couple of years.

Harrop might be the most widely used in the LS community. Mast Motorsports makes engines that use the Harrop, DSE uses it in their White Monster 5th gen Camaro. But I think any of the above vendors could be successful as long as the engine and desired performance parameters are spelled out clearly in advance, the system custom configured to requirements, and good EFI tuning available (ITBs present quite different challenges to the ECU in low throttle situations).

Biggest advantage of a true ITB in a streetable application is the ability to use a dramatically larger cam (specifically, larger in the sense of more overlap) while still maintaining idle quality and lower RPM drivability. That's because the close proximity of the throttle blades to the intake valves creates a much smaller total intake volume that is under vacuum, and therefore a smaller volume of exhaust reversion during overlap.

Also, an ITB is typically easy to "tune" for optimal effective runner length and thus maximum peak torque RPM.

The biggest downside to ITB is that creating an effective filtered cold air system often robs a good deal of power. It's not an issue of "flow" per se, it's that most air supply manifolds partly suppress the finite amplitude waves in the intake runners - those pressure waves that help pack the cylinders before the intake valve closes. Creating custom air supply manifolds with large volume is important to minimizing this loss.

[supremeefi]

[QUOTE=PTAddict;578145]I have no experience with any of the above, although I've researched a lot and plan to add a Harrop system in my car in the next couple of years.

(ITBs present quite different challenges to the ECU in low throttle situations).
Correct. So make sure you get an ECM that will allow you to change cyl to cyl fuel trim at not only idle but other areas of the rpm range. There are only a few that allow you to do that.

Biggest advantage of a true ITB in a streetable application is the ability to use a dramatically larger cam (specifically, larger in the sense of more overlap) while still maintaining idle quality and lower RPM drivability. That's because the close proximity of the throttle blades to the intake valves creates a much smaller total intake volume that is under vacuum, and therefore a smaller volume of exhaust reversion during overlap.
That's not the only reason. You now have no dirty air, all throats are isolated from the exhaust reversion from other cylinders.

Also, an ITB is typically easy to "tune" for optimal effective runner length and thus maximum peak torque RPM.
[QUOTE]

Hope this helps.

[OVRKILL]

PTAddict prett much touched on the highlights.

I run a Kinsler on my LS based 460. Big cubes, huge heads, any yes, a big hyd cam 260/270 .680/.680 @ 113. Idles like a 383 at 850rpm.....WOT however is a different story. :unibrow:

If set up properly in runner/blade balance, you shouldn't need a ECU that tunes cyl to cyl....don't get me wrong, it would be nice, but necessary.

Don't think you can go wrong with either of them, but it would solely depend on your build and want you want out of it.

Soooooo.....what are we building? Street, show, Autox? Considered selling my set-up if you're interested....heads half to go with, btw.

[PTAddict]

I have no experience with any of the above, although I've researched a lot and plan to add a Harrop system in my car in the next couple of years.

(ITBs present quite different challenges to the ECU in low throttle situations).
Correct. So make sure you get an ECM that will allow you to change cyl to cyl fuel trim at not only idle but other areas of the rpm range. There are only a few that allow you to do that.

Biggest advantage of a true ITB in a streetable application is the ability to use a dramatically larger cam (specifically, larger in the sense of more overlap) while still maintaining idle quality and lower RPM drivability. That's because the close proximity of the throttle blades to the intake valves creates a much smaller total intake volume that is under vacuum, and therefore a smaller volume of exhaust reversion during overlap.
That's not the only reason. You now have no dirty air, all throats are isolated from the exhaust reversion from other cylinders.

Also, an ITB is typically easy to "tune" for optimal effective runner length and thus maximum peak torque RPM.


Hope this helps.

Not really sure why cylinder to cylinder fuel trim would be more important in an ITB setup. It is actually easier to make each cylinder "see" the same intake tract in a properly designed ITB setup than in a conventional common plenum intake. Adjusting the individual throttle blades to be consistent is obviously very important, of course.

I have a slightly different point of view on your dirty air comment - I can easily envision a design that has big long runners with throttle blades at the very ends which will create just as much exhaust reversion as a common plenum intake. And most "street" intakes have some common vacuum channel as well. But it really isn't worth arguing - in practice ITB intakes suffer much less from exhaust reversion with big cams than conventional intakes do, and that's all people need to know to understand the advantages.

[supremeefi]

Not really sure why cylinder to cylinder fuel trim would be more important in an ITB setup. It is actually easier to make each cylinder "see" the same intake tract in a properly designed ITB setup than in a conventional common plenum intake. Adjusting the individual throttle blades to be consistent is obviously very important, of course.

Correct but I've done a few Hilborn systems that had blade problems on a couple of throats. Being able to change cyl to cyl trim kept it from popping at idle.

I have a slightly different point of view on your dirty air comment - I can easily envision a design that has big long runners with throttle blades at the very ends which will create just as much exhaust reversion as a common plenum intake. And most "street" intakes have some common vacuum channel as well. But it really isn't worth arguing - in practice ITB intakes suffer much less from exhaust reversion with big cams than conventional intakes do, and that's all people need to know to understand the advantages.

If they're isolated then they don't share the others dirty air at the wrong time.
I've done a few where they had tunnel rams or other common plenum intakes first. Idle rpm's ranged from 1100-1400 rpm's and were rough no matter what. Once they got a properly tuned true isolated IR intake all of them idled at 800 and where as smooth as silk. Not sure what else it could be, you?:)

[PTAddict]

If they're isolated then they don't share the others dirty air at the wrong time.
I've done a few where they had tunnel rams or other common plenum intakes first. Idle rpm's ranged from 1100-1400 rpm's and were rough no matter what. Once they got a properly tuned true isolated IR intake all of them idled at 800 and where as smooth as silk. Not sure what else it could be, you?:)

Not disagreeing with your empirical observations, just your analysis. I should just let this go, but the pedantic engineer in me comes out :) The rest of you, feel free to whack us on the head.

Let's do the thought experiment. Is it possible to create a 1 cylinder engine that idles like crap with a big cam? Absolutely. Just put a big enough intake plenum after the throttle body, which can accumulate enough exhaust reversion to create the gagging effect that is lumpy cam idle. No adjacent cylinders needed :) But in practice with a 1 cylinder engine, chances are the throttle blade is close to the intake valve, and the volume under vacuum when the overlap cycle commences is therefore very small. So the amount of reversion is correspondingly low. An ITB engine is just eight one cylinder engines.

[supremeefi]

I have no experience with any of the above, although I've researched a lot and plan to add a Harrop system in my car in the next couple of years.

That's because the close proximity of the throttle blades to the intake valves creates a much smaller total intake volume that is under vacuum, and therefore a smaller volume of exhaust reversion during overlap.



But that scenario goes away when you introduce a common plenum of any significance, whether it's an IR or not. I'll stick with my own opinion and personal experiences. Thank you for yours though.