On an otherwise stock engine, on the marks is generally close enough for most quality stock cams and timing sets.
Sometimes manufacturing errors are made, and it becomes necessary to "correct" those errors. Errors can be made with the cam grind, and the timing set also. Corrections to the event timing may become necessary to make the engine run as intended.
For performance applications, degreeing the cam is necessary, if only to verify that the cam timing events are occuring for best power in the rpm range intended. Advance and retard can move the power to where it is most advantageous to the application.
I'll see if I have a part number still floating around the shop. There are odd and even sets. I'll verify what I have. Can't remember at the moment!
CJ
