![]() In older engines such as from the ’40s and ’50s, the vacuum advance signal came from the intake manifold. This is typical in earlier mechanical fuel injection and lean burn carbureted engines since the late ’60s. More recent electronic ignitions modulate spark advance for different driving conditions. Vacuum advance if so equipped – variable up to 10 degrees, typically added with engine vacuum more advance usually at low engine speed.Įlectronic limiting of ignition timing is also added for smog control requirements. Initial advance – typically 10 to 15 degrees before TDC (top dead center)Ĭentrifugal advance if so equipped – typically up to 20 degrees before TDC, added with engine speed more advance with high engine speed Ignition Timing Control – Open Loopįor open loop systems commonly used in a carburetor or mechanical fuel injection: Ignition timing trendsĪs RPM increases, more ignition timing is neededįor higher octane fuels, more timing is needed due to slower flame speedįor large combustion chambers, more ignition timing is neededįor forced induction, less timing is needed because of faster flame speedįor emission controls, less timing is used to reduce smog compoundsįor richer fuel mixtures, more timing is needed due to slower flame speedįor alcohol fuels that are run richer than gasoline fuels, more timing is typicalįor nitro fuels that are richer than methanol fuels, even more timing is typical. This is done with a combination of initial advance, plus centrifugal or electronic controlled advance for engine speed, plus vacuum or electronic advance for engine loading and throttle effect. ![]() ![]() ![]() Best power is achieved when ignition timing is set to fire the spark ahead of time to reach that peak pressure at about 2 degrees after TDC. ![]()
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