Big Blocks Not Rocket Science
As stated in my post the specs given are applicable to high altitude (Albuquerque varies from 4500 to 7000 ft excluding the peak which is 10,700), and as Duke says, with my altitude and 110 octane leaded fuel I probably have unlimited room for advance. With that said, the Chevy Power Book and every guy who has raced Chevy motors for years (Clem) knows that sea level track specs are 38 total mech advance. Why estimate your total? Take off the distributor cap and rotor, remove the springs, make sure the rotor is NOT advanced before you start it - then start it, use the idle screw to take it up to anywhere between 1300 and 2000 rpm, and measure the crank advance. Set it to 38 using your dial back light (vacuum can disconnected of course). You are guaranteed that all the advance is in. This simulates wide open throttle above 5000 rpm. Let the initial be whatever it is - most of these distributors have about 28 built in, which sets you up at 10 true initial for 38 total. If you time your car using this method and if you use good enough fuel all these minor differences in vacuum can starting and ending points are moot except at partial throttle driving. If your car overheats you have other problems. For those guys having hard starting and/or backfire issues - your distributor is off a tooth or two, or your starter needs to be reworked to solve the heat soak problem.
As stated in my post the specs given are applicable to high altitude (Albuquerque varies from 4500 to 7000 ft excluding the peak which is 10,700), and as Duke says, with my altitude and 110 octane leaded fuel I probably have unlimited room for advance. With that said, the Chevy Power Book and every guy who has raced Chevy motors for years (Clem) knows that sea level track specs are 38 total mech advance. Why estimate your total? Take off the distributor cap and rotor, remove the springs, make sure the rotor is NOT advanced before you start it - then start it, use the idle screw to take it up to anywhere between 1300 and 2000 rpm, and measure the crank advance. Set it to 38 using your dial back light (vacuum can disconnected of course). You are guaranteed that all the advance is in. This simulates wide open throttle above 5000 rpm. Let the initial be whatever it is - most of these distributors have about 28 built in, which sets you up at 10 true initial for 38 total. If you time your car using this method and if you use good enough fuel all these minor differences in vacuum can starting and ending points are moot except at partial throttle driving. If your car overheats you have other problems. For those guys having hard starting and/or backfire issues - your distributor is off a tooth or two, or your starter needs to be reworked to solve the heat soak problem.
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