<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Geoff:
Also, using the 'advertised duration' will give varying figures. If you use a Comp Cams hyd, they usually quote their hyd cam figures at 0.006"; Crane often use 0.004" . Could get a different DCR for essentially the same lobe profile because of a difference in the quoted 'advertised duration' figures.
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The difference that 0.002" makes in valve closing angle is extremely minimal. The actual calculated difference turns out to be negligeable. The only truly accurate way to determine intake valve closing angle is to measure it yourself using a degree wheel and a gauge that measures piston height. All other means (most of them involve basing calculations on the cam duration) are a "best guess" which can be plenty accurate for baseline figures. This is why I added a means to manually enter the closing angle, some people have gone through the process of measuring it themselves.
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Geoff:
The very fact that it is called 'dynamic' means that it is changing. And that is exactly what it is doing, constantly: changing. I feel there are too many variables involved to get DCR from a formula or equation. <HR></BLOCKQUOTE>
Actually no, the dynamic compression ratio does not change throughout the RPM range, it is fixed. Just because it's called "dynamic" does not mean it changes. I agree that it's a misleading term to use, but it wouldn't be the first technical event that's poorly named
In this case "dynamic" refers to the fact that the compression ratio can be varied independantly from the static compression ratio (ie. with cam timing).
There's a few excellent explanations for dynamic compression available on the web. Jim Hand wrote one, and there's another article that's been pointed out numerous times in this very thread.
Anyways, cylinder pressure isn't measured as a ratio. That wouldn't make any sense. Cylinder pressure is measured in psi.