Have to know the CC size and deck height then figure in compressed gasket. I went through all this 4 months ago and found some good calcs they might help but you really have to know CC size or else its anyones guess. At least you dont have to worry about recessed pistons like my 5.3 I never did figure out the volume they take away.

heres the link
http://www.wallaceracing.com/Calculators.htm

I played with the numbers alot and finally came out with an approximate of 10.5:1 with my heads milled .050 but this is with dished pistons.
Assuming your heads are close to the stock CC volume, maybe .020 off and flat top pistons I would expect you to be in the range of 11:1 maybe higher depends on how much are off the heads.
I forget how much the deck height is on a stock 5.3 I know youre having your engine rebuilt Im assuming yours would be stock. Maybe someone will jump in with that figure.

Oh and have fun tuning Im still working on getting my tune right.

 

IF your 11.4 original number is really correct, and the pistons are set to stock height using a stock gasket, then...


10.85:1
Final Answer.

 

LOL

I know it's all IFy.. I just wanted to try and get a ballpark figure.


Thanks for the scare in that motor PM Richard!

 

Thank YOU for your help Justin.

10.85:1 is a very close number, trust me. If you decide to run thinner than stock gaskets, it will be a tad higher.

 

NP buddy

I was hoping for over 11:1 CR on this motor but no biggy. If anything the lower compression will help me pass smog easier and 10.85:1 is still pretty high. Should be a pretty responsive motor if we got the cam right.

 

It's just a close guess with out all the info.
CR varies on stock motors because the deck height varies. The pistons can come out of the hole anywhere from .006 to .012 on an LS1 motor, depends on which one you check. Mine are .010 out on the 5.3.
The bore size of the gasket can change cr. If you put a 5.7 gasket on a 5.3 and they're the same thickness, the larger bore size will lower cr.

 

Understood.

I was also guaging how well this motor would nadle a 100shot if I decided to make a few passes in the 12sec range just so the truck doesn't feel like it went too far backwards.