When it comes to camshaft timing events, I am challenged - no matter how much I learn about this or how many times I degree cams it remains confusing to me.
So those of you who are more familiar or comfortable with camshaft timing, please help me answer some questions I am curious about. Let me say that this post is entirely about the published specs for this cam, and not about my degreeing results at all.
I have reproduced the Clay Smith cam card for this cam (H-280-0-BHL), exactly as it came from Clay Smith,
but with the addition of "Descriptor" columns that I need to remind myself about the terminology that cam manufacturers use (degrees BTDC for intake opening, degrees ABDC for intake closing, degrees BBDC for exhaust opening, degrees ATDC for exhaust closing). It's easier for me to wrap my limited mind around camshaft timing if all events are referred to
in the same coordinate system -
ATDC.
Notice the
Centerline Timing Events row, with values of
108 INT and
112 EXH. What does this indicate? To me, this may indicate that there must be at least some difference between the camshaft timing on intake vs. exhaust:
Let me put on my mad scientist hat here: If Clay Smith cam lobes are symmetrical (as several here have stated), then it looks to me that the intake centerline should be in the exact center of the .050 duration, which should be 108 degrees
at the .050 numbers on the cam card: (assuming that the cam is ground straight up, or before any advance is ground into the cam)
Intake Opens (.050): 7.5 BTDC (-7.5 ATDC)
Intake Closes (.050): 43.5 ABDC (223.5 ATDC)
Duration @ .050: 223.5 - -7.5 = 231 degrees
Half (Midpoint) of Duration @ .050: 115.5 degrees
Intake Centerline: -7.5 + 115.5 = 108
Poke holes in my theory.
If the above is correct, I'm going to suggest that the cam is called a "110 degree centerline" cam, but the 110 is an average of the 108 degree intake centerline and a 112 degree exhaust centerline.
Thanks
Bob