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Old 08-25-2009, 06:48 PM
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philminotti philminotti is offline
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Join Date: Aug 2004
Location: Orange, CT
Cobra Make, Engine: KMP 736 Street, Pond 482, FAST XFI EFI
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Lou-

I'm by no means an expert, but static compression ratio is, by definition, static. Valve events have no bearing on the calculation. Which is why the SCR is really not terribly useful when picking a cam.

You need to calculate the dynamic compression ratio. I like this calculator: http://www.kb-silvolite.com/calc.php?action=comp

As you can see, it's really the intake valve closing point, or the number of degrees past BDC that the intake valve closes, that most effects the DCR. So yes, a more "radical" cam can have the effect of bringing a high SCR into a more manageable range, at least as far as octane requirements go. Naturally, there are other factors such as emissions, fuel consumption and driveability that are also affected.

Hope this helps.

phil
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