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Post by Admin on Feb 7, 2019 3:07:55 GMT -5
Here's the distributor for a 1972 Ford Mustang MaCh 1 with 351 Cleveland HO... Rough and rusty, still with points stuff. Owner to install pertronix electronic conversion unit after it's all refurbished and re-curved... Yuck... and two mechanical advance choices as is... "18L" or "13L"... currently utilizing "13L". These numbers indicate how much the distributor will mechanically advance with increased rpm, with the rpm at which it advances start to finish dictated by springs. Distributors turn 1/2 the rpm that the crankshaft does. "18L" indicates a mechanical advance of 36° BTDC... which doesn't leave much room for a healthy amount of initial ignition timing. "13L" means 26°, so that leaves room for about 10-12° BTDC of initial ignition timing, for a total mechanical ignition advance of 36-38° BTDC. Not bad, but 10-12° initial isn't ideal either for something with a bumpier camshaft in it. Cleaned up. Let's get started with a re-curve... The math to do this... to limit one of the slots for less mechanical so that more initial can be set... is as follows... JB-Weld and some filing of the "18L" slot... Measure the radius from distributor center to the post center... To create the equivalent to a "10L" slot. Diameter is radius X 2. Circumference is diameter times pi. Inches per degree is Circumference divided by 360. Ready to go, with up to 18° BTDC initial timing allowable, and with a new vacuum advance that only pulls 6° degrees (12° crankshaft) .
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