408 Cam on the way
I put a screen shot of the compression calculator in post 102. How I did the CC accounting for the step and dish is in post 115.
A 0.070 gasket puts it at 9.5.
All my numbers are the averages taken from rocking the pistons. Thanks for asking.
Not beating a dead horse but my math is your CR is 8.53:1 not the 9.5:1 your showing.
Here are my numbers using what you’ve posted.
836 cc’s for the full cylinder
.520 down fill is 109 cc’s
Your down fill is 131 cc’s
Your dish volume is 22 cc’s
Your chamber is 61 cc’s
Your gasket is 15 cc’s
I’m making a bit of a guess on your gasket volume because you’ve posted the gasket thickness but not the bore diameter. I used a bore diameter of 4.080 as a guess. It may be slightly smaller, or it could be bigger.
When you add up the actual dish of 22 and the gasket of 15 and the 61 of the chamber you get 98 cc’s.
Then it’s the division of the swept volume of the cylinder which is 836 by your total volume of the chamber of 98 and you get 8.5306:1 and no doubt my math could be wrong.
I know from the years I have of doing this the number one killer of engine performance is the mismatch of CR and cam timing. If the CR is lower than you think and you cam for the higher CR it’s lazy and under performs.
If you miss the other way and the CR higher than you think and cam accordingly it will rattle its brains out and be miserable to tune.
Before doing anything I hope several members check my math to see if I have gotten sideways somewhere. If my math is correct you have a full point lower CR than you have posted.
I hope I’m wrong.
EDIT: I AM WRONG AND YOU ARE CORRECT. I woke up at 3 this morning and realized I forgot to add in the chamber volume, gasket volume and the dish volume to get the total swept volume. When I do it correctly I get 9.53:1 and this is the perfect example of why I shouldn’t do math late at night after not getting any sleep for the 3 days prior.
So...my bad and I apologize.
YR
