In simple terms, it means to advance the camshaft timing.
In general, advancing the cam will pull the power band down to a lower rpm, retarding it tends to move it up in rpm.
On a cam card, the actual degrees of opening and closing is shown as advertised or at .050".
This is what my card shows;
BTC -8, ABC 22, BBC 37, ATC -13.
These are the timing locations in degrees of the flywheel where the cam makers wants the valves to open and close. You use these when you degree a cam in using a degree wheel and dial indicator. If the cam is ground right, you could install it with a straight key and line up the marks on the gears. If you found the cam was off a bit, you could put a offset key in the camshaft and move the timing from a 1/2 up to 5 or 6 degrees either way. The idea is to get as close to the cams timing as you can.
When advancing a cam, you would use the same offset keys and move the whole timing event ahead or behind of what the cam card shows. Its trial and error as to how much you move it. To really tell if it works, you need some drag strip times before and after the changes.
Joe
