Valve timing vs. advertised duration

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02-21-2007, 03:41 PM

AJay

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Valve timing vs. advertised duration

I have read Cam threads ad nausium regarding duration at .050 which everybody seems to use for defining how a cam will perform but why aren't people focusing on the actual Intake and Exhaust Valve opening and closing events? It seems to me that you could have two cams with a duration of....say...224/228 with different valve opening and closing event times which would perform completely different from one another.

So why is everybody using duration at .050 as the gospel?

Last edited by AJay; 02-21-2007 at 04:44 PM.

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02-21-2007, 04:26 PM

Ragtop 99

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I refer to the timing at .006 as "advertised".

We actually do pay attention to seat to seat duration.

Comp lobes are the most common and so when you see people talking about an Xe, XER, or LSK lobes, the difference amoung lobes reflects lift & seat to seat duration for a given .05 duration.

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02-21-2007, 04:38 PM

Ryan02SS

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Quote:

Originally Posted by AJay

I have read Cam threads ad nausium regarding advertised duration at .050 which everybody seems to use for defining how a cam will perform but why aren't people focusing on the actual Intake and Exhaust Valve opening and closing events? It seems to me that you could have two cams with an advertised duration of....say...224/228 with different valve opening and closing event times which would perform completely different from one another.

So why is everybody using advertised duration as the gospel?

The .050 duration is the common spec all cams manufacturers agree upon. The advertised duration is not agreed upon and different companies use different numbers. Comp uses .006 where almost every other cam company use .004. Isky, Crane etc.. Using .006 makes the open and closing valve event look faster than the .004 number. If you compare the advertised numbers of a cam, just make sure they are both at .006 or both at .004.