I cant seem to get this question answered in any other threads so i will start my own. all this talk about high performance LT1/4 intake manifolds really has me wondering. at what point in horsepower does your intake manifold become your bottle neck? I mean are we only talking 9,000rpm stroker motors that are over 400cubic inches making over 700rwhp naturally aspirated? From the pics on his site, it looks like hoover was running a lt1 intake manifold or a LT4 intake manifold and he got a hair over 500rwhp i think. and like i have said in other posts. i would think his bottle neck would be elsewhere like in the fact he was only running 1 3/4 inch headers instead of 1 7/8 inch headers with AFR227 heads that flow a lot more than the heads he had on it. or the fact he was only running 36lb injectors. My point in all that is how much rear wheel horsepower do you have to be wanting to make to where a ported and polished LT4 intake manifold isnt going to give you what you need?

 

anybody?

 

Airflow isn't everything, first off... It's not that the LT manifolds won't support power, they will to a point (usually around 550-600 hp naturally aspirated and ported). The problem lies more within their layout; these manifolds are simply not optimized for the combinations that a lot of people are assembling. We went from one extreme to the other between the TPI's (with 25" of runner length to the top of the valve) to the LT1-4's (with 9" of runner length to the top of the valve). Generally it is known that the ideal length is more in the 11.5"-14" range. The LT manifolds with their 3" runners are also highly subject to intake reversion on large cams (the kind you typically find on bigger/more radical combinations). This causes not only disruption of the air/fuel flow but can also be a tuning nightmare. Those with LT1's or MR motors with large cams with considerable overlap I can pretty much bet experience low speed bucking and some topend intake resonance; all due to reversion with a big cam. The simple fact is the LT manifolds are excellent manifolds but they aren't optimized and are far from perfect on radical combinations. They are oriented to a very narrow powerband due to their runner length. They can be improved considerably but in order to really work them over it is often necessary to cut and reweld the manifold.
-Jeb

 

-Jeb[/QUOTE]

The thing to keep in mind is that both intakes were designed for F-bodies not neccessarily performance. The TPI is designed for 305 motors that needed to lug all that wieght around. The LT1 intakes was designed to fit underneath the F-body hood.

The Superram is a MUCH better length but with one problem...it forces the air charge to change directions at the head. This is why acell went to producing their top of the line fuel injection systems with modified single planes.

The TPiS Miniram is still a non-rpm-tuned version of the LT1 intakes but with a longer runner...slighter more lower rpm tq...which for the Miniram is about 4500-5000 rpm. This is of course at the expension of a smaller volume plenum which then causes a rich/lean off balance between cylinders in some motor combinations.

 

I cant seem to get this question answered in any other threads so i will start my own. all this talk about high performance LT1/4 intake manifolds really has me wondering. at what point in horsepower does your intake manifold become your bottle neck?

For ressonance
TPI 5000 RPM
Superram 5800-6000
TPiS MR 6900-7400
LT1 8000?

for hp/TQ
for flow take the max CFM divide by the displacement to get the max RpM for a max TQ. The tricky part and the reason why you didn't get any relevant answers is that motors only work at 100% fill on one part of the torque curve. The trick is to build RPMs (shorter runner length) faster than you lose cylinder fill YET have it idle.
TPI 198 CFM
SR 250-265 CFM
MR 300-340 CFM (anyone have a better number)
LT1 260?

So a smaller motor will make more HP->Honda
A bigger motor needs flow but tuned at a lower RPM->396 SR
Then there are nuts like me who have motors that will rev to 7000 if I let it, but are relying on the higher flow of the MR versus the TQ built from ressonance

 

if the lt1 is 260cfm, divided by a 396 stroker thats about a max rpm of 6500rpms or so (ballpark) i wonder if you ported and polished an LT4 intake manifold if you couldnt get it to flow close to 300 cfm. that would be great cause then it would be close to matching a good set of heads (ie 290-310cfm) and would make ur max rpms over 7k. not that you need to be revving a smallblock well over 7k but i would like to be able to rev a little higher than 6500 and still make good power. does anyone here know what CFM flow a highly ported and polished LT4 intake flows?

 

Ideally the manifold should always flow at least 15% more than the cylinder heads.
As for ported LT4 flow the best numbers I've seen have been right at 300 cfm; MR will flow a little more. I've seen MR's that have been cut in two, reworked and then rewelded that flow in the 320-330 range. But again; flow numbers aren't everything. The design of the intake runners, the plenum, and how it works with the camshaft (the brain) and the heads (the lungs) plays a larger role than flow alone.
-Jeb

 

quote from someone more knowledgeable than myself..."I just tested this on an LT4 intake last week. I used a factory LT4 head that I'm about 90% done with. On the head I've worked the intake side to 205cc and it flows 275 @ .600. With the unported LT4 intake bolted up to the head on the bench it flowed 230.5 @ .600. After fully porting/welding the LT4 intake (includes raising the runner) the combo flowed 251.8 @ .600. Peak gain 21.8 cfm."

It will take me some research time, but I can PM you a lot of good info in this area...if you're really serious about it.

 

i am serious about it but most likely not untill a lot later. i am planning a cam swap soon but i will probably stay with stock heads and wont really need heavy duty porting untill i decide to do a stroker motor. im just curious if it looks like i can get the power i want out of a stroker motor with the stock LT4 manifold if i port and polish it enough

 

anyone else have any input?