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GMC Jim · 08-05-2003, 03:12 AM

ddsmith... you asked "how to determine the correct advance to use to set the distributor to"......the factory shop manuals should list these specs. In my case; the specs for a 402 engine are listed at the back of the '1971 Chevrolet Truck Service Manual'; Distributor specifications. Example for the 402 engine the centrifigal advance degrees is 0 @ 930 RPM; 2 @ 1260; 16 @ 2400 and 30 @ 4400. The vacuum advance should be 0 @ 8" and 20 @ 17". Another GM manual "1971-80 Tune-Up Specifications" states the the total advance ( vac. and cent.) should be 28-35 @ 2000 RPM. About 10 yrs ago, I had a qualified distributor rebuild shop set the proper advance curves; checked the mechanical and electrical components. This distributor rebuild firm had the specs on file also....I installed the distributor, replaced the spark wires with those designed for the higher voltage produced and gapped the new spark plugs to .045....Very pleased with the performance and increased gas mileage............ Jim

08-05-2003, 03:12 AM	#13
GMC Jim Senior Member Join Date: Dec 2002 Location: Portland, Oregon Posts: 901	ddsmith... you asked "how to determine the correct advance to use to set the distributor to"......the factory shop manuals should list these specs. In my case; the specs for a 402 engine are listed at the back of the '1971 Chevrolet Truck Service Manual'; Distributor specifications. Example for the 402 engine the centrifigal advance degrees is 0 @ 930 RPM; 2 @ 1260; 16 @ 2400 and 30 @ 4400. The vacuum advance should be 0 @ 8" and 20 @ 17". Another GM manual "1971-80 Tune-Up Specifications" states the the total advance ( vac. and cent.) should be 28-35 @ 2000 RPM. About 10 yrs ago, I had a qualified distributor rebuild shop set the proper advance curves; checked the mechanical and electrical components. This distributor rebuild firm had the specs on file also....I installed the distributor, replaced the spark wires with those designed for the higher voltage produced and gapped the new spark plugs to .045....Very pleased with the performance and increased gas mileage............ Jim __________________ '71 GMC;fleetside;PB/PS/AC/CC/402 Eng./Custom Paint/110,000act miles/3 fuel tanks(52gal).