My buddy just bought a lQ4 motor with cast iron heads, and will be installing new pistons and rods bored .03 over. Our goal is around 600-800rwhp with a t76mm

We want to know before we order new pistons and used aluminum heads to get around 9.5 compression, should we get dished pistons and smaller chamber cc heads or flat top pistons and larger cc heads? What are +/- of either route?

example run 243s 64 cc and -13/14ish range pistons

or mimic the stock set up with 72 cc heads and -7 pistons

 

You will need a Bigger turbo

 

haha I have been telling him to run around an 88mm size and that he is probably only going to see 500 with his t76, but its not my money lol

goal is to run 10-15psi

 

The hp range is wide. 600 doable with a 76. 800 maybe but not a mid size unit.
An 80-88 on the compressor side would be easier.

Sorry no help on the head/piston combo.

 

Im running -4cc .03 over with stock 317 and ls9 gaskets and that put me aound 9.8:1 compression ratio. But I only "plan" on 5-600 hp.

 

It all depends on on the rest of your build OP. Is there any chance this truck will be going back to being N/A at some point? If so I would run less of a dish piston and hit your compression ratio with bigger combustion chambers.

 

Correct me if I'm wrong but didn't the cast headed lq's have a different length crankshaft, requiring different flexplate/flywheel and/or TC...might be something to check into before he commits any money to the project.

 

i believe they didnt require the spacer on those like the aluminum headed ones.

 

What fuel will you use?

 

I built mine with -11cc pistons and run a ported 241 head with ~66cc chambers and a stock mls gasket for a 9.85:1 cr. I want to upgrade to an aftermarket head with taller decks but it is hard to find them with the smaller cc chambers and big valves for a large bore motor. If I were to do it over, I would use a smaller dish piston and adjust the cr with the head. From a mechanical efficiency prospective, I have no idea if the large dish/small chamber has any advantage over small dish/large chamber or vice versa.