A couple of months back as I was browsing through Vette Magazine I came across an interesting read. The guys were building an LS2 and during the build decided to try out different intake manifolds available. The interesting bit is this :

1) The stock LS1 manifold performed almost identically to the larger LS2 manifold with the bigger TB opening until 5500 rpm.From there, the LS2 bested the LS1 by as much as 11 hp. Part of the credit surely goes to the larger 90mm throttle body on the LS2. BUT get this the LS1 made more peak TQ! 471 VS 469 !



2) The stock LS6 manifold beat the LS2 manifold. The LS6 intake not only produced more peak power than the LS2, but it also outperformed the newer-style manifold from 3,700 to 6,500 rpm. The guys even suspect that with a larger TB the difference would have been even MORE !



Link to article :
http://www.vetteweb.com/tech/vemp_0612_ls2...otor/index.html

Theories ? This is sure confisung the hell out of me. I have my theory but wanted to hear the expert opinions. Mine has to do with the amount of air fed into the intake. I am no expert so correct me if I'm wrong.

Well I am not an expert on such things, but I do know a little engine theory from reading on the subject.

One thing I am aware of is that air flow through a manifold does not act like you would think it does by common sense. This is because the opening and closing of the valves causes disruption of flow and corresponding pressure waves that can either aid or impede vacuum-induced air flow, and it happens more or less so at various RPM. This is why a smaller intake can generate higher torque than a bigger one, and why bigger manifold/TB is not always the best solution, particularly for lower RPM operation.

It is interesting that at higher RPM where the engine is making more power, it may actually be getting less air per cylinder charge than at lower RPM, even though if you measure TB air flow you will certainly see more air flow at higher RPM, because the motor is simply going through the whole process faster, hence more total air flow per second than at lower RPM.

It also accounts for why my 225 HP L98 can generate 330 ft-lbs of torque at 3500 RPM - induction tuning - hence the name Tuned Port Induction. This tuning effect is very significant on my car with 17 inch runners. At certain RPM, the pressure wave returning to the cylinder meets an opening intake valve and consequent vacuum, and the two work togther to increase air flow into the cylinder far beyond what vacuum alone would pull.

This manifold tuning effect is present on every motor. Longer runners tend to increase the significance of the tuning effect, making higher torque at lower RPM, but sacrificing HP by restricing flow at higher RPM. On my motor it is the most significant factor in accelerating the car and is why the motor was named after the manifold tuning effect. On cars with lower runner length, manifold tuning is significant, but may not be as significant as it is on the L98.

The key is to match the manifold and TB to the heads/motor/exhaust to get the power curve you want, which would depend on if you want speed (hp), gas mileage, or pulling power (torque) such as a truck.

That's just air flow, then you have to look at spark and fuel, which is yet more levels of complication. This stuff gets pretty complex if you really want to do it right.

The LT1 went for horsepower by reducing the intake runner length to almost nothing, but lost the pedal response so loved by the L98 crowd, becasue it killed the midrange torque- minimal induction tuning effect. The LS1 attempted to balance everything back out and get a good compromise between horsepower on top and torque in the mids.

Does that help?

YES, the secret therefore lies in the runners eh ?. Can we discuss further ? The LS2 intake was supposedly an LS6 intake further revised. So I would have thought that it would match up with the LS6 numbers. But this is not what happend here. It seems the camshaft selection didn't go well with the intake. I think because of the faster camshaft , the bigger intake isn't getting enough time to flow enough air hence lower power output. The smaller ones are doing a better job. Am I on the right track ?

Well, in a specific case like this I am not sure I am qualified to assess it, but generally speaking I would say to get the most out of a set up, you have to match the cam to everything else. So a cam with high lift and moderate duration would be more suitable for a longer runner, and a long duration cam would be better with a shorter intake for higher RPM applications. I think more lift is an improvement in all cases, duration is the one that will affect induction tuning more. Now this is not to say that you may not get a good strong motor with some mismatching of components. I am simply saying that you can optimize torque, horsepower, or reach the best compromise bewteen both, by carefully matching components.

I am not really well versed in the LS series intakes, help me out here. LS1 came in 1997 with the C5, LS6 was the C5 Z06, LS2 is the C6 base motor, and LS7 is the C6 Z06. Is that right? This would make LS2 a larger and slower flowing intake, better for a 400 CI, higher RPM application. LS6 would have been a tighter intake to optimize flow on a 350, bigger than LS1 but smaller than LS2. So it would make sense that the LS6 would show more mid range torque, and might even show more horses if well matched to the rest of the set up. However, with the right set up the LS2 might do better, it depends on the cubes, cam, and heads. So see it's a lot of variables that go into this stuff.

Yep you are right on the LS series. Then we both agree. In this specific application the LS6 performed better but that does not generally mean it is a better intake than the LS2 i.e. like the magazine states. Goes to show you though how one component is vital to the entire system.
For my built motor , we are going with the LS2 intake btw. It'll be a forged 346 , but with Trick flow heads,custom ECS blower cam, the intake would make a good match while shifting 14~15 psi . Hopefully right in its sweet spot

And it is notable that the results did not vary widely with the various LSx intakes. I don't think you could go wrong with any of them, but I do think the LS2 will be superior for a blower application, for whatever my opinion is worth. Things are bit deifferent with a blower because you are pushing air in rather than pulling it in as with N/A. If you were pushing the same amount of air as the motor would draw under vacuum, then the flow dynamics would be similar I think. But you are pushing more with a blower (hopefully, no point in doing it otherwise ) so the problem becomes restriction at the top end, where the blower really gives you the boost you are looking for.

I think with a blower you are looking at a similar situation to trying to set up a high RPM motor - you want maximum flow at peak RPM. You don't want to lose all your mid, but the compromise point for a blower application would lean more toward the high RPM power side than it would for a N/A motor. So bigger and/or shorter runners is the way to go, and the boost in the mids will help offset the loss of torque due to less induction tuning. LS2 for sure.

And a little lift extension on the trailing end of the exhaust lobes of the cam.

So, sounds like you are putting a monster together there. 15 PSI on a 346 ...


I'm sure ECS will fix you up with the right components, much better than my informed guesses. I forsee some fine kill stories coming out of that set up.

Yep. Initially I wanted to go bigger cubes but after a lot of discussions with Dave,Doug & Chris we all decided that 346 was the way to go. Tried and tested. ECS uses the best components in their builds and I have been dealing with them for a while so the comfort level is present. I've gone into some details of the build in the Killer Lounge.
Can't wait to install the new heart into my baby

Well it depends on what you want of course. John Lingenfelter said " There is no replacement for displacement." I think he was quoting an old hot-rodders maxim.

John was speaking in terms of making the fastest quarter mile run. And he was right.

When you bring in some other factors like long term reliability, fuel economy, cost, suitability for routine driving, etc., then I have to agree that the time-proven SBC 350 platform is clearly the sensible choice.

Sounds like a winner man.

Basically the arguement against the bigger cubes is:

"Why blow up your trans/rear for 20k when you can do it for 10!"

Good point. It's quite possible to build a 346 into something that will require a major upgrade to the rest of the drive train to really be useable. If you don't want to do all that tranny/axle/rear stuff, then the 346 is already more than enough.

For that matter, you can get outrageous horses out of smaller cubes. The low and mid torque is where the cubes come into play and the 346 has plenty for street.

Thats about it . Well lets hope the FLT Level 5 4L65E,DTE Diff Strut and the RPM Built Diff hold the shit down