Compression Ratio

[BeachMonkey100]

Just need some double checking on the CR of my motor. When I cc'd the heads after I un shrouded the valves I averaged 53.5cc's, then proceeded to have .015" decked off the heads. I did not cc them after this for some unknown reason.

So here are some specs to help,

3.554 bore
3.543 stroke
-8.3cc dish piston

Why I am ultimately making this thread is because somehow or another I lost my notes measuring piston deck height. If I remember correctly they were .005" in the hole, the block was never decked just cleaned up.

So what I did for calculating the CR is I took a compressed gasket thickness of .038" (average compressed gasket thickness) unless someone knows of a more accurate number otherwise and subtracted the .015" I decked off the heads making the thickness .023".

So using the information above I get somewhere around 9.68:1 CR.

Anyone have any input on this? Where something might differ from one another? Reason I bring this up, Lito asked what it was before we go heavy into tuning on pump gas and trying to figure out a stopping limit before I switch and start tuning on E85.

 

[Dino Dino Bambino]

Removing 0.015" from the heads will reduce the chamber volume by ~2cc so yours will be ~51.5cc. The deck clearance volume will be 0.8cc so if you add the 8.3cc dish volume and a 6.7cc head gasket volume (assuming 3.7" HG bore and 0.038" thickness), the total combustion volume will be 67.3cc.
The cylinder volume is 576cc so the compression ratio will be:

(576+67.3)/67.3 = 9.56:1

 

[BeachMonkey100]

That's probably a lot closer and more precise than what I thought I had.