Quote:
Originally Posted by Gaz64
...can use timing to help stabilise idle speed, which is half of how EFI does it. You can't do that with fixed timing...
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Gary you nailed it.
By having the ignition advance increase below the desired idle speed, and increase above the desired idle speed, a V shaped ignition advance curve is formed. At the bottom of the V is where the desired idle RPM should be. A V shaped ignition advance curve will form a extremely fast, self correcting feedback loop that will help lock down the idle speed. We had an over-cammed 427 powered GT40 come into the shop to be sorted out. One of the issues was if the engine was idling, and if the AC was turned on, it would stumble. By advancing the timing below the desired idle speed, the idle stumble was eliminated.