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Spark advance at high/low Kpa's

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Old 12-31-2001, 02:19 PM
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Car: 1997 Jeep Wrangler
Engine: 4.0L
Transmission: 5 speed
Axle/Gears: 8.8 rear, 4.56 gears, 4:1 transfer
Spark advance at high/low Kpa's

Why can't I run as much spark at high or low Kpa's as I can in the middle Kpa's?
Old 12-31-2001, 03:54 PM
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Car: 78 Regal
Engine: 82 FBod LG4 305, 730 ECM
Transmission: M20
Axle/Gears: 4.10
That's more of a question related to the mechanical side of the engine, but since an ECM can detect where the engine is operating, it can also help it like a mechanical ditributor never could. The lighter the load (low KPA) ususally means that the engine is coasting or some other lean mixture mode and also that it's at lower engine speeds. This means you can run higher advance in order to burn all the fuel charge as it is less volatile. The opposite is true for high load: more fuel, more volatile, and less time to burn it. Very general statement here so take it FWIW.
Old 12-31-2001, 06:11 PM
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Car: 1997 Jeep Wrangler
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Axle/Gears: 8.8 rear, 4.56 gears, 4:1 transfer
General, yes. But I understand now. I was just curious.
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