> How do you compare two cams using 0.050 numbers when one runs
> with a valve clearance of 0.010 and the other runs at 0.030? Not a very
> useful standard.
As I understand it, the .050" standard came about both because it's harder to
measure seat-to-seat (because of the slow ramps that start and stop the valve
motion), and because the first .050" or so of valve motion contributes little to
breathing. Lift and duration is not all there is to a cam profile ... for some
American engines you can even buy a "cheater" cam that meets all the factory
timing and lift specifications but breathes significantly better, by the simple
technique of opening and closing the valve faster.
Some interesting information at :
http://www.iskycams.com/degreeing.php
Randall
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