Quote:
Originally Posted by cgarr
The more overlap the less static compression. It can make a huge difference but that's not how you should be setting it.
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Valve timing is not part of the static compression calculation.
Valve timing affects dynamic compression. The higher the overlap the lower the dynamic compression.
Quote:
Originally Posted by polizei
After having the top end of my 3.2L Carrera rebuilt with used 3.3L Mahle cylinders and pistons, the leak down numbers are coming back OK but the compression numbers are really low (average 80 PSI per cylinder). Cylinders were re-ringed. Heads received a valve job and were twin plugged. Moved to 964/993 twin plug dizzy and added an Andial splitter. What do you suspect the problem(s) could be?
The compression test was performed multiple times by a pro and yielded the same results. Thanks for your help!
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3.3 production 930 pistons have an advertized compression of 7:1.
If they have valve pockets that number goes down. By simply changing the deck height to .060" the compression ratio goes down. .020 deck change will reduce the compression by .24:1.