friend of mine was sold some heads by the shop who built his motor. its a 383 LS1, so i guess the bore is 3.903 on that. the heads have a 2.08 intake valve and it isnt making much power.

what he had before was 2.02/1.60 valves....pete from cnc heads did them in florida. LS6 intake, 80 mm TB, 224/232 114LSA camshaft. the car made 632 rwhp through an A4/12bolt with that setup.

he wanted 700 rwhp so he decided to upgrade some stuff. he went with those huge a$$ heads(per their recommendation), FAST 90MM intake, 90MM TB, and a huge cam...248/254 i think....not sure why the hell they went so big?? cam was supposed to be 242/248, but after they degreed it they see that its 6º bigger on both sides!

he also converted over to a 200r4 GN tranny with lockup converter.

they had to add more timing to the old program just to make as much power as it use to make. they(shop) are telling him the tranny is using up more power...my friend and i disagree. we think they are just making excuses for their ****** heads!

thanks for your replys in advance!!

Yeah 2.08 heads and chambers really don't go well with the 3.900 bore. We do these all the time and you have to run the right stuff for the bore or the airflow isn't even really better 90 per cent of the time. Also the exhaust side might like the bigger valve more than the intake anyway depending on the boost although 1.600 at his level os probably plenty.

That's because they probably ground a regular SBC lobe without the 55mm master. Going from 1.868 to the 2.166 tunnel will do that if you don't order it right. Also there can be some bigger than you would imagine differences between trans and converters on auto cars.

even if its locked up?

i think he got the tranny fully rollerized too....whatever little bit that might help.

what valve size do you recommend for the 3.9 bore?

It depends on the port and the chamber but 2.02 works very well and we have had some 2.055 stuff also do alright. It depends on teh chamber and how big the port is. I like the 2.02 the best and you can go over 310 cfm with that anyway.

ok, thanks...

I doubt valve size is the problem, maybe bad combustion chambers. But most likely is the cam is just too big for the static compression of the motor and not enough RPM to get in the cams powerband which will be quite high.

yeah, i think he should have stuck with the cam that was in it. i think he made 550rwhp @ 7psi with the 224/232. so i guess its a pretty good little camshaft...

UPDATE!!!!!

switched out JUST the heads and it made 750 rwhp! bought a set of the cheap little patriot performance heads(LS6 style) for $1349 i think.

amazing that he made over 100 rwhp by switching to a smaller head. and 1600 bux less too!

oh yeah, went from a 2.08 intake valve and flowing 330CFM@600, to a 2.02 valve flowing 305!

I can't see how going from 330CFM to 305CFM and a different sized valve is going to make that much difference. You would think that with a force inducted engine, the more air that you can force through, the more HP you are going to make. I know that a lot of times velocity means more than flow numbers, but that much? It makes me wonder if it was more in the tune with the previous heads than with the heads themselves. But, it's hard to argue with the numbers.

I think velocity only matters in a N/A car, but I agree with you that going to a smaller size head shouldn't increase power with a supercharged motor. The only thing that I can think of is that maybe the valve tran was to weak on the other set of heads.

nah, i'm pretty sure it was the valve size. 2.08 is huge for a 3.903 bore!

nothing was changed in the tune.

Well, the reason I am curious is that I am using AFR LT4 210's on my forced induction buidlup and they have 2.08 intake and 1.60 exhaust valves. Of course, it is going to be 4.030 bore with a 3.50 inch stroke crank for 357 cubic inches. I don't know if that will be a difference and of course with the head design difference and everything between the LT1 and LS1, it may be comapring apples to oranges.