This is a typical cam-lobe profile, courtesy of COMP Cams. Here are allof the dimensions and what they mean. This is the anatomy of both camlobes as they relate to each other. "A" is the opening ramp of theexhaust lobe. "B" is the base circle, where no valve activity occurs."C" is overlap, which is also when the exhaust valve is closing and theintake valve is beginning to open. "D" is the closing ramp of the intakelobe. Retard/Advance shows us which way to turn the camshaft to advanceor retard valve timing.