CR Help

[1972_911T]

Just been trying to get an estimate of my CR and I get two different figures by two different methods which is most likely to be accurate?

Basically its a 3.0 with twin plug heads and 9.8: pistons. Dome volume measures 38cc's head volume is 85 deck height is 0.8mm I put all this into an online calculator and get 10.6:1.

Next I bolted on a head and measured combustion volume and get 46cc's, so with a head volume of 85 - 38 for piston dome plus 5 for the volume of the deck height this would equate to 52 so off by around 6cc's.

So cylinder volume 499 + 52 = 552 / 52 = 10.6 as with my other calc

or going with the measured 46cc's 546 / 46 = 11.8

So 2 very different figures and both quite away away from what the CR should be is there anything else I can do to confirm either of the estimations? I have a feeling with the second method I may not be getting complete chamber filling.

Steve

[1972_911T]

Mystery Solved, just had another go at cc'ing the combustion chamber and moved the engine around to get all the air out now I get a combustion chamber of 56cc which works out at 9.9:1 Im sure this is more accurate than measuring the heads and piston dome it's hard to decide when the heads are full due to the miniscus and due to the diameter just been a mm or so off will make a big differance.

Steve