Advancing and Retarding:
By advancing the cam, the valves open and close earlier. Duration and overlap remain unchanged. Advancing raises the cylinder pressure (due to earlier valve closing) This improves low end and mid-range torque at the expense of some top-end power. The result is similar to using a shorter-duration cam since the intake valve closing point is more critical than its opening point.
Retarding the cam so valves open and close later has the opposite effect. This should increase top-end power, at the expense of low end, and mid-range torque. Thus: 1) Advance Cam: More low and mid-range torque, 2) Retard Cam: More top-end power.
Advancing and retarding are easily accomplished with offset bushings or keys for the cam or crankshaft, depending on the engine. The bushings and keys are usually supplied in increments of 2, 4, 6, and 8 crankshaft degrees. Remember that one crankshaft degree equals two camshaft degrees.
How Much is Enough?
Trial and error is usually the best method when advancing or retarding a cam to alter performance. Our experience indicates that cam advance of 2' to 6' should give the best overall performance. These settings have helped top-end power in many engines.
Before attempting to advance or retard a cam, you must know the actual valve timing, not the manufacturer's specifications.