zo6vette

if i bolt on 5.3 heads on my Ls1 with this increase horsepower?

6speedZ28

I believe to get any power increase those heads would have to be ported.

MISOMWS6

If they are just stock 5.3 heads it prolly won't do much, i'm pretty shure they will give you a slight bump up in compression, so you may see a small increse. I'm shure someone will know the exact compression ratio.....I can't remember it at the moment

Demon SS

as a direct bolt on it is not worth the effort. it will raise your compression from 10.1:1 up to 10.9:1 so in theroy that would give you a slight more power all things being equal, BUT the 5.3L heads have a 1.89 stock intake valve while the 5.7L heads have a 2.00 intake valve so the 5.3L heads don't flow as well in stock form.

Now ported you have a different story. We have a project car with ported 5.3L heads and a largish cam (plus other mods) that runs 11.4's at 120mph in the 1/4(car is an M6). Car has not been dyno'd yet but we estimate it to be about 460rwhp

Taspeed

Demon is right. Take a set of 5.3's and have 2.02's put in on the intake side. That should get you some hp. Now optimally you would want to have some porting done, but in stock form I picked up about 20hp with unported 5.3 and a little valve work

Demon SS

Hey Taspeed, you need to send those 5.3's to me so I can work em over for ya, then you can go give Scott J. a run for his money

We do a killer set of 5.3L heads (or any heads for that matter)