I have heard in some applications people retard the timing in high gear. Can someone explain why this is? What are the benefits, better top end? Less chance of pre ignition at the end of the run ?
In the dark ages, long, long ago, on my street car, I set my dual point distributor up with different positioning than what they came with, to back one set of points off as much as 4 degrees from the other, and ran the advanced points wire to a toggle switch on the shifter. Up, full advance, then, in third and fourth, switch down, 4 degrees retarded, was worth at least a tenth.
My thought was that most drag cars looking for quickest et. the engine gets cooled before the round, so it can use more timing & as it heats up down track it needs less timing.
I've never heard an "official" explanation from anyone who's done serious engine dyno work on this phenomenon, but your comment does make engineering sense.
It has to do with the actual temperature of the burn in the combustion chamber, and what happens when areas of the chamber don't uniformly heat/cool, creating alternate flame light off and frontal areas. To help cool the burn down when it gets to optimum temperatures and passes that limit, the timing is retarded, so there aren't any alternate flame fronts to create pre-ignition and flames colliding in the chambers.
Sometimes, it is intentional, others, not so controllable.
If anyone has ever had a chance to "play around" with any sort of electronic ignition on a distributor machine, most electronic systems will self retard, for various reasons, past a certain output level, a couple of degrees. The GM HEI is usually good for two to three degrees only after a certain rpm it has limited to for a couple of thousand rpm's. Two stroke motorcycle engines like as much as 4 degrees after they lock out within a curve.
MSD used to offer a stand alone single, and then, two stage retard add on units, and their 'AL' series boxes, already had/have upper rpm timing retard.
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