Yes, another compression ratio thread

[buddy]

so if i understand that right by adding the .01 gasgets minus the .004 that it was decked and adding the .02 for the lager pistons i should be at like .026????????? im confused i really want to understand how all this affect each other but i always end up giving up cause i get a head ach!

If you are looking at total decrease in CR, then you went down about 0.62 points total. Thats about 0.6 down for the gasket minus the decking, and .02 for the pistons. Although if you upgaded to diamond precups that would have lowered the CR by about a whole point. I think it would be amazing that they could take just 0.004" off the deck, thats precision and must mean you didnt have any pitting.

Here is an updated version of the file to give a little more flexibility and info. For decking, you can put a negative number in the one cell you can customize under head gaskets. Using the CR you started at (stock for example), see what decking did then insert that CR value to see how other changes affected it.

 

[Ratman]

The lower compression height, is that acheived by shaving the pistons or are the swirl bowls still full depth? youre probably looking at about 18.5:1. The diamond precups are what brings the CR down from like 21.3:1 to 20.2:1. That was GM's method.

The 18:1 Mahle pistons have the wristpin relocated, the tops, Ricardo bowls, and ceramic/anodize are identical to a stock piece.

Rumor has it they are no longer being made due to low demand.

Thanks for the help, -I figured it was closer to 19, but 18.5 is fine by me. That would probably explain why I haven't pushed the gaskets out yet.

 

[chevyCowboy]

im not sure on the .004 thats just what the machinest told me. i cant remember but its seemed to me that the pistons stuck out of the holes just a touch, they where almost flush