OK..I know Absolute speed has some of the best 5.3 heads.
I think I know the compression ratio is around 10.8-1..?

NOW.... WHAT WOULD be the HP increase if i was just to swap on a set of 5.3 in place of my 5.7? no other mods!

I know that stock LS6 heads(10.5-1)cr are worth about 10hp more than
LS1 heads with a(10.1-1)cr.

I want to be running the Lingenfelter GT2-3 cam in the future with 5.3 heads.

will it give me 400 hp at the wheels?

 

With the 5.3 heads having a very shrouded 3.80" bore chamber and a very small 1.89 intake valve then I would say the 5.3 heads would make less power stock then a stock 5.7 castings. The real benefits come from porting these heads properly, opening the chamber to 3.90 bore and installing a 2.02 intake valve. Hope this helps. BTW, I went 9's with our 5.3 heads.