Been lookin at some hptuner logs with a tuner and my car drops from 100 kpa @ 2800rpm to 96kpa past 5000. So its obvious that the engine is not getting enough air in to reach full potential.

My car has a torquer v3 cam (231/234 .644/.598 111lsa) w/ prc duals and supporting mods.

I have: Lid (sealed to debaffled hood for ram air), smooth bellows, SLP MAF (screened), ls6 intake, stock ls1 heads, longtube headers, ory, catback w/ e-cutout.

Are my heads the problem? Is the ls6 intake the problem or is something else going on?

 

I've been searching for an answer to mine pulling a vacuum at WOT as well, but mine doesn't ever seem to get beyond 96-97 kPa from the start of a WOT pull to the very end. It is something that has baffled me for the longest time, and I've checked many things, but the car still runs great, so I've just kinda let it be. Good luck with yours...if you figure it out, would you let me know?

 

The Map sensor reads the vacuum in the manifold so I don't think it takes into account restriction in the cylinder head...I think a vacuum would signify a restriction upstream. Could be throttle body, could be intake manifold, could be MAF, could be air lid (probably a combination of things). Better heads will pull more air through the intake manifold so the better the heads are, the better the supporting mods upstream better be.

FWIW, I removed my 85mm MAF and replaced it with a 3.5" pipe and gained 1-2 kPa in reduced vacuum. I expanded my air lid and smoothed my air entry into my TB. Every little bit helps.

 

Oh yeah forgot to mention, i did some slight porting and smoothing on my tb as well.

 

I'm not an expert or anything, but from my reading on this forum. It seems the LS6 Intake can be a restriction as heads nowdays are not the week link and flow more than the intake. I think one of the sticky's said that the LS6 Intake only flows 280 cfm's. Unless you go boosted and push more air.Heads are beyond that nowdays. That's just my observation from all the reading.

 

I would say the restriction is more in the heads. if the LS6 intake flows 280 cfm thats not too bad considering the 241 heads only flow about ~250 cfm.

 

Yes the heads are a major restriction to him making more power, but that has nothing to do with his question. His MAP readings are in the manifold so the reduced pressure is because of a restriction either in the manifold or somewhere upstream. Everything in the whole intact system is a restriction, so anything that you can do to make more air flow the better, but I would say that probably the biggest restriction is the manifold/TB.

 

Ahh see that was my problem in school lol, i just scan through things and jump to a conclusions. But you are right, everything is restrictive.