Thought I'd get a rise out of that one!
The reluctor on the HEI has 6 triangular projections that align with the similar-shaped pole shoes on the pickup coil. When these align, an AC voltage is induced into the pickup coil, which triggers the ignition module. At speeds above normal cruise, enough voltage is developed to interfere with the pickup coil's ability to set up for the next firing impulse, causing spark scatter. On the roundtrack V-8's, when we're required to run a stock-appearing distributor, I grind off every other point on the reluctor, leaving 4 instead of 8 projections. It still aligns 8 times, and fires all the cylinders because the ones on the pickup coil aren't altered. It works the same way on a 6, except 3 instead of 4 points are removed. This reduces the induced voltage, and allows 1,000 RPM or more to be gained before spark scatter occurs. A stock V-8 HEI starts to spark-scatter at about 6,000 RPM, and with the mod, it will go to nearly 8,000. Since we run the roundtrack engines about 6,500 or more, I can out-wind the guys with the unmodified distributors. On competition-only engines, we also disable the vacuum advance, and bolt the advance plate solidly to the distributor housing to eliminate plate wobble at high RPM. Since the 6-cylinder HEI is almost identical to the V-8, it works for them, too. We also reduce the centrifugal advance about 10 degrees, and advance the initial timing the same amount to increase acceleration without over-advancing. A good distributor tester is essential to set up the advance curve properly for best performance.
Jerry
