[jpnovak]

John, Here is my findings on the inconsistant sign, It has been a while since had to do algebra.

from first section.

"a. Peak HP Engine Speed = (exhaust duration degrees * 66.62) - 9083"

from second section.

"Ballpark Exhaust duration (in degrees) = (Peak HP engine speed – 9083) / 66.62."

Its been while since I have done this math but. IF I use the first equation and add 9083 to both sides of the equation I end up with:

Peak HP + 9083 = exhaust duration * 66.62 and finally

(Peak HP + 9083 )/ 66.62 = exhaust duration which is not the equation in the second post. I am not sure which sign is correct.

I can tell this thread is going to be very helpful to me and others. Its good to be able to understand what a builder or cam grinder is talking about. I think the second equation should be a minus sign. this would give 38.7 deg of overlap for the S cam graph above. This fits in your suggested range.