Compression ratio, is this right???
Compression ratio, is this right??? Getting ready to swap some heads on & figured I would see what my CR would be at 62cc. This is what I keep on getting, which seems correct for static, but the dynamic seems way too high. Am I entering something wrong? I've tried it on a few different calculators, all with the same results. I included my cam card if that helps. Thanks.
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From: Sparta, Mo. in southwest Missouri
The problem that I see with your dynamic compression calculation is your intake closing point. I hate to point out that your not putting in the number your calculator is calling for to begin with. They're calling for your intake closing point + 15*, which in your case would be 59*. The calculator I use and others I have seen call for the ACTUAL closing point, which in your case would probably be closer to 70* ABDC. The reason is that you're trying to find the actual compression ratio of the engine which is when the cylinder is actually closed so that the piston can start compessing on its way to TDC. Comp Cams uses .006 to figure there advertised duration whereas Crane and some others use .004. You might call them and ask the closing point at .006 or if you are degreeing the cam, you can check it yourself. I like the calculator at this web site the best...www.not2fast.com. It's free, and has various other calculators as well. I tried your numbers on their calculator, using 70* ABDC as your intake closing point. Came out at 8.21:1 DCR and theirs showed 10.77:1 SCR. Cheers, Ron
Last edited by rojs234; Feb 17, 2011 at 10:04 AM. Reason: figured the numbers
Thanks for the info. I just used a formula I found somewhere else to figure the ABDC for DCR purposes & also came up with 70, so that makes a lot more sense now.
Thanks again man, I was a little worried earlier. Didn't want to have to run race fuel.
Thanks again man, I was a little worried earlier. Didn't want to have to run race fuel.
