My car is tuned with GM graphite head gaskets installed, but I pulled the heads to find that they were blown, so my question is if I switch to cometic .40 gasket, will I NEED to get the car retuned and how much power should I pick up? Car has Torquer2 cam, prc ported ls6 heads, fast 90, numbers in sig.

 

you wont pick up any power, the tighter quench will help prevent detonation a bit though.

 

with that cam, youll want to make sure your PtoV clearance is ok running a .040 HG. whats the chamber volume on those heads? im assuming you have a stock bottom end, so you dont have valve reliefs. if its going to be tight, then you might want to look into a .045-.053 MLS gasket. but you have to do your calculations and check PtoV to be 100% sure of everything.

and you will make alil more power if your up'ing your compression. what youll really see/feel is a boost in low end torque. I dont know the compressed thickness of a graphite gasket, but say its .053 and you go to a .040 then yes, i would look into getting the tune looked at to optimized your setup.