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The Mighty Pieholio
Bob Kontak's Avatar
Join Date: Nov 2007
Location: North Canton, Ohio
Posts: 12,866
Originally Posted by 2jmotorsports View Post
I am having trouble calculating my CR because I "eyeballed" TDC when I measured deck height. I may go back and re-measure it while setting TDC with a dial indicator. Maybe. Im getting kind of tired of all the precise measuring.
Another side bar:

Engine Builders Supply fly cut my heads to clean up for the new seal. They removed 0.006". I just looked up the formula for cylinder volume and did a little math and found 0.006" is worth 0.2 points of compression.

Years ago, I posted my math on this forum and it was confirmed.

So, 9.3:1 went to 9.5:1. I used standard (copper?) spacers at base of cylinders. Reason I knew they were standard spacers is Bruce Anderson's book talked about using fatter spacers if you went overboard.
1981 911SC Targa
Old 11-10-2017, 12:50 PM
  Pelican Parts Technical Article Directory    Reply With Quote #101 (permalink)
Under the radar
Trackrash's Avatar
Join Date: May 2007
Location: Sebastopol, The Republic of California. Land of wine and redwoods.
Posts: 3,902
FWIW. My recently assembled SC motor's heads measured 89cc. IIRC the spec is 90. The JE 9.5 - 1 pistons ended up giving me a 9.8 - 1 CR.

I wonder if the Carrera heads have a slightly larger combustion chamber?
'71 911 Coupe 3,0L outlawed
#56 PCA Redwood Region, GGR, NASA, Speed SF
Old 11-10-2017, 01:43 PM
  Pelican Parts Technical Article Directory    Reply With Quote #102 (permalink)

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