I decided to open my valve reliefs up this spring, I needed a little more clearance and the ability to run larger valves, cam, or ratio rockers if I ever wanted to. I had Mahle forged pistons in 16 to 1 form with .050 reliefs big enough to run a 34mm intake valve and a 33mm exhaust valve. We widened the pocket .100 and deepened it another .100 to a total of .150. I'm looking for thoughts on how much that affected my compression ratio. I've been told as little as a half point and as much as 3 points. The pistons were 47cc before modified and it lightened them 18 grams. Thoughts?

By my rough calculations you removed about 6.4 cc from the pistons. You should be able to use a compression calculator to figure out where your at now.

Ok thanks Bill. I don't know all the other values but should be able to find out. I have a friend who has 43.5 cc pistons. I need to find out his ratio and then I'll be closer.

Try this, http://www.csgnetwork.com/compcalc.html , just enter the values you know and compare the pistons, should get you in the ball park. Are you having issues that make you think you went too far?

No Bill, I haven't ran it yet. I just got concerned talking to my tuner the other day.

Kinda nervous about mine, de-lipped stock pistons with .075 valve reliefs. I'm worried it'll be a b!tch to spool if it's too low.

My pistons were .040 over. Do you have a guess where I'd final out compression wise?

Not knowing all the variables, head gasket thickness, head cc volume (if any), exact piston volume, piston protrusion, ect, I would have to make a rough estimate of around 15.5 to 1.

Head gaskets are decked block gaskets at this time because I used to have .020 protrusion with Crower's now only .0025 with the carillo's. My head guy was pretty sure of in the 15.5 to one range too but I had a couple guys guess 13:1. That scared me a bit I must say!!

My motor is also stroked a 1/4 inch I should add.

So your using the GM "special" head gaskets? They're supposed to be even thicker than C's. Stroke shouldn't effect compression much as long as piston pin height is in the right place. I'm assuming your using Guy's whole stroker package? Playing with the numbers some more, I would say your no lower than 15 to 1.

So your using the GM "special" head gaskets? They're supposed to be even thicker than C's. Stroke shouldn't effect compression much as long as piston pin height is in the right place. I'm assuming your using Guy's whole stroker package? Playing with the numbers some more, I would say your no lower than 15 to 1.

Yes on the whole stroker and yes on the gaskets being thicker than the C's.