Camshaft Percentage

[alakso]

Mike, in Mr. Rook's book he talks about using "Cam percentage" as a way he uses to compare different cam grinds. I've tried 20 different ways with my calculator to figure this out. The closest I came was by comparing intake and exhaust duration but still the numbers don't jive.

Mike would you be so kind to explain "cam percentage" and the formula for figuring out cam percentage?

[Mike]

I have not done the math but what "cam percent" repesents is the difference in total cylinder cuibic inches that includes cam intake opening and closing times, based on piston position, vs actual cylinder cubic inches, based on cylinder volume/piston from TDC to BDC only. This is expressed as VE potential. For example, a 100ci engine would have a one cylinder displacement of 50ci would ( = 100% VE when filled with air). Since the cam opens and closes the valve BTDC and ABDC, this increases cylinder cubic inch volume when the added volume for the piston pisition for each of these events is added to the base 50ci. With a Wood TW 6 cam (20/40 with 240 duration), this increases cylinder volume to 56ci (approx). So 56ci is 112% of the base 50ci. This is the cams VE potential for that size cylinder, percent it "occupies" the cylinder or said to have a percentage of 112%. It's, generally, another way to represent duration.

[alakso]

Thank you so much Mike. This answer alone is worth the price of admission!