Every engine has a powerband. A powerband is an rpm range during which the engine yields the most power for the work it's doing. Some engines are designed so that the powerband comes in early, like diesel engines, inline six cylinder engines, and most big blocks. They get their power right away, but they peter out sooner, too. Others are designed so that the powerband starts later, but lasts into higher rpms.
You with me so far?
Changing the cam timing moves the powerband either higher or lower. Advancing the cam timing 4 degrees will lower the starting point of your powerband by 500 to 800 rpm, whereas retarding the cam timing by 4 degrees will raise the rpm at which the powerband begins to hit by roughly the same amount.
Cam timing is changed with a special crankshaft timing gear that has multiple keyways, so it can be put on at slightly different positions, ultimately advancing or retarding the cam timing. The best way to decide where to set the cam timing is to try it in different positions, and then run a compression check after each one. The cam timing that gives you the highest compression readings is the best for your specific engine combination.
Hope that helps!
Take care,
~Chris
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