[Kurtdg19]

Advancing timing basically means that your spark plug will fire earlier before TDC. What this essentially means is that it allows combustion to happen a little earlier BTDC than normal. This will give the combustion more time create the pressure from the explosion so when its going down on the powerstroke, it tends to 'hit' harder. This will be more noticable in lower to mid rpm ranges. However; it will hurt high rpm. This is mainly since the pistons are traveling faster they don't need that extra time to create the combustion pressure. Too advanced timming will cause pinging and pumping loses high up the powerband. Retarded timming will do the opposite, helping more on higher rpm and less on lower. Of coarse as far as performance goes, its always best to have the timing as far advanced as possible, but not to the point where it starts to ping (and thats when you know its too far).

Engines are already designed to change timming accordingly to a point, so whenever you do decide to advance a little or retard a little you should consider how its going to effect the engine.