Compression Calculator
 

Anyone have an online compression calculator they TRUST? I am putting the same specs in at Wallace Racing and Butler Performance and getting two different results. Wallace Racing says 9.2:1 and Bulter says 8.5:1. Pretty big difference.

Here's the specs:

Bore: 4.16 (400 +.040)
Stroke: 3.75
Heads: 92cc
Valve Relief: +10ccs (Icon Pistons)
Gasket Thickness: .045 (crushed)
Deck Clearance: 0.00

I wrote the one on the old classicalpontiac website, made it back in the '90s. People have been using it for nearly 20 years now, so I'm pretty sure it is reasonably accurate.

EDIT: Yep, ONE of those calculators has a problem!

EDIT #2: I agree with the Butler calculator, I get 8.46:1, which is what I'd expect with that size head.

Ok, Wallace is the outlier. Classical, Butler and Summit all say 8.46:1. Wallace has the value 6.6 in by default for valve relief (guessing due to TRW pistons being +6.6). If I change that value to 10 then I get 9.2:1 on his calculator. If I use -10 I get something over 11:1 so 10 or +10 is right. Seems his calculator is just off for some reason.

I get 8.41 on the Wallace Calculator. I assume the .045 gaskets have a 4.3 bore ?

Ran it twice @ 400 + .040, 92 cc heads, 10cc reliefs, .045 x 4.3 gaskets, .000 deck height. CR = 8.41

If I don't enter anything into the gasket bore box, I get 9.19 CR. So, what did you guys enter for the gasket bore size ?