-Spark Advance and Max Power-
common performance engines

Ignition timing plays a critical role in the power and longevity of an engine. The degrees of advance determines when the cylinder begins to "fire". is what actually happens is the air/fuel mixture ignite and begins to burn, expanding the air with the heat of combustion. if this occurs too soon the piston will try to move backwards and cause stress on the crank, rods and pistons. If there is enough inertia to keep the piston moving upwards it can blow head gaskets or crack pistons.
If the timing is too slow the mixture does not burn efficiently enough to produce maximum power at or slightly after TDC. This leads to extra heat being produced that is not transmitted as mechanical force. Slow timing can burn Valves, melt pistons, and crack exhaust manifolds from extreme heat.

It becomes obvious very fast that proper ignition timing is essential for any high performance engine that operates at or near it's maximum potential. This graph illustrates common ignition timing for a performance V8 engine. Lower efficiency requires more timing while greater efficiency needs less timing.

Some critical factors that affect required ignition timing are the compression ratio, the octane rating of the fuel, the cam specs (specifically overlap), the weight of the vehicle, the altitude, ambient temperature and more. There are three types of advance a common performance engine can have, "locked", mechanical and vacuum or any combination of the three. The most common is the mechanical with vacuum advance. Generally speaking vacuum advance should not be used on a performance application as it is mostly for fuel economy and emissions. If vacuum is used manifold vacuum is better than ported.

As a general rule of thumb ignition timing should be 10-12* at idle for a stock cam, 18*-20 at idle for a performance cam and should max about 36-40* by 2800 rpm. The mechanical advance can be adjusted by using different weights and/or springs in the distributor.

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