To the best of my knowledge, HEI distributors were designed in the era of 7.5 compression and restrictive bead type catalytic converters. On those motors these supplied advanced curve works perfectly, but with Magnum engines you want the timing to come all in by 3750 and be limited to about 30/32. The stock curve on the silver spring HEI weights is all in by 4500 and maxes out at 50°. I followed Uncle Tony's advice on the HEI distributor and put a weld bead in the advance slot, then filed it down till it only moves 30°. Then I put the heavyweight and light spring kit on it so timing is in by 3,500.