[email protected] (Dave Williams)
mustangs  18 Jun 1993

-> know how it fits into the picture of determining HP and Torque.
-> Also, why is .050" so important?  I still haven't been able to figure
-> that out.

 As the cam lobe comes up, there's a takeup ramp that takes all the
slack out of the valvetrain, loads the valvetrain until everything
is flexed, and then the lobe comes up and wallops the valve open.  On
the other side, the lobe lets the valvetrain close at a rate determined
primarily by the valve spring, then decelerates in a curve designed to
keep the valve from bouncing off its seat.

 A "280" cam might have an actual off-the-seat time of 280 degrees, but
depending on the ramps and lobe shapes, you could have vastly different
camshafts.  The industry has more or less standardized on .050 as a
checking figure - from .050 up, most cams of a given type (street, road
race, drag race) are fairly similar.

 Not everyone uses .050, though.  Checking at .006 is common.  Ford used
to use .100, some companies use .020.  It's hard to get a straight
answer from some places - the "advertised duration" figure usually tells
you only how lopey the cam grinder feels the cam is.  For example,
Competition Cams adjusts the advertised duration according to the lobe
center - a smaller lobe center cam will be listed as a longer duration,
*even if it has the same identical lobe* as a wider center cam.

 If you have an old Stock Car Racing from (November, I think) 1990,
there's a good-sized cam article explaining how a lot of this stuff
works.  I wrote it.