setting up the gen III for rpms or torque
06-15-2010, 09:25 AM
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setting up the gen III for rpms or torque okay, i am htinking about building up my lq4 a little now that the swap is running. i want to make this thing a torque monster. do you guys think it will be able to deliver more torque to the rear wheels by just building a torque motor, or building the motor to rev a little more and then gearing it down a lot. i'm really not sure if theres much difference, so i'm pretty much just brainstorming here. but i do want to start looking at cams and such to plan the build, so i guess my instinct is to just build it for torque, but then the lsx seems to like revs more than the old traditional sbc. is that strictly a function of cam design though, or are the bore/stroke relationships or some block design features different enough to matter? any thoughts? i'm going to get my IC engine design books out and see what i cna find, but if anyone on here has thought about this i'd like to hear what you found. thanks
06-15-2010, 10:14 AM
#2
If you spin the engine 8k, it will not produce any more torque where you need it than if you were to go to only 6500.
If you want torque, cubic inches is the easiest way to go. Building a 402 or 408 with higher compression will get you there. Do not use a huge cam either. That will also point you in the wrong direction.
The LSx style engines are not confined to the "norm" of a lightweight rotating assy that the SBC had to have, just to get revs out of it.
I would use a good aftermarket head like TFS with a runner at/under 235, cncd or not is your choice, and run a camshaft under 23x intake/23x exhaust with as much lift as you can cram in there on a somewhat wider LSA than most of the big name cams like a 114-116.
Depending upon intended use, keep your CR under 11.5 and you will be good for just about anything (assuming a good tune).
If you want torque, cubic inches is the easiest way to go. Building a 402 or 408 with higher compression will get you there. Do not use a huge cam either. That will also point you in the wrong direction.
The LSx style engines are not confined to the "norm" of a lightweight rotating assy that the SBC had to have, just to get revs out of it.
I would use a good aftermarket head like TFS with a runner at/under 235, cncd or not is your choice, and run a camshaft under 23x intake/23x exhaust with as much lift as you can cram in there on a somewhat wider LSA than most of the big name cams like a 114-116.
Depending upon intended use, keep your CR under 11.5 and you will be good for just about anything (assuming a good tune).
Last edited by Beau@SDPC; 06-15-2010 at 10:39 AM.
06-22-2010, 08:13 PM
#4
Okay, you say you want a torque monster, but by this do you mean you want it to just be torquey in everyday driving (<3000 RPM's) or do you ACTUALLY want maximum rear wheel torque/acceleration. I'm going to assume you want the latter as this is the only interesting one to talk about.
From a theoretical standpoint:
The simple answer is you want as much RPM as possible - so long as you get components that will work at that RPM. Here's why:
Naturally Aspirated, you are limited in the VE you can achieve. For the most part, VE is going to be pseudo-proportional to torque output (disregarding non-linearities in frictional losses). Now because we do not have the luxury of completely variable valve timing, variable intake runner lengths, variable length/diameter exhaust, etc..., you have to choose WHERE you want your peak VE/torque. You have a choice of 100% VE/500 lb-ft at say 3000 RPM or 100% VE/500 lb-ft at say 6000 RPM.
If you gear the 6000 RPM car twice as much as the 3000 RPM car, it will put twice the torque to the rear wheels and still shift at the same speeds. This is a gross over-simplification, but under the rough theoretical limits established above, this is fundamentally true. Properly setup, more RPM is always better. More RPM increases the 'effective' displacement of the engine.
This is very fundamental theoretical stuff and is easy to prove. You want to make peak torque at as high an RPM as you can so long that peak power RPM+500 RPM is still at or under your redline.
If you would like more technical discussion on this ask away.
From a theoretical standpoint:
The simple answer is you want as much RPM as possible - so long as you get components that will work at that RPM. Here's why:
Naturally Aspirated, you are limited in the VE you can achieve. For the most part, VE is going to be pseudo-proportional to torque output (disregarding non-linearities in frictional losses). Now because we do not have the luxury of completely variable valve timing, variable intake runner lengths, variable length/diameter exhaust, etc..., you have to choose WHERE you want your peak VE/torque. You have a choice of 100% VE/500 lb-ft at say 3000 RPM or 100% VE/500 lb-ft at say 6000 RPM.
If you gear the 6000 RPM car twice as much as the 3000 RPM car, it will put twice the torque to the rear wheels and still shift at the same speeds. This is a gross over-simplification, but under the rough theoretical limits established above, this is fundamentally true. Properly setup, more RPM is always better. More RPM increases the 'effective' displacement of the engine.
This is very fundamental theoretical stuff and is easy to prove. You want to make peak torque at as high an RPM as you can so long that peak power RPM+500 RPM is still at or under your redline.
If you would like more technical discussion on this ask away.
06-24-2010, 03:50 PM
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IMO, I ran Hedmans 1 1/2 stepped to 1 3/4 headers and didnt think much of it. I switched to a full 1 3/4 header and felt a drastic reduction in midrange torque. So obviously my vote goes to careful selection of exhaust manifolds.
