Distributor Vacuum Advance Motor
Thread Starter
Melting Slicks
Joined: Sep 2000
Posts: 2,404
Likes: 418
From: Chester Virginia
Distributor Vacuum Advance Motor
What is the correct/best vacuum advance motor for my distributor. The distributor is used on a stock 1973 L-82. According to the service manual the advance should start at 6" Hg, and have a maximum of 15deg at 12"Hg. The engine has a vacuum of 13" Hg at an idle speed of 700 rpm. I have the Accel adjustable motor but its response range appears too short. Just wondering if someone might have a GM part number or a NAPA part number for a vacuum advance motor with the above specification.
Roger
Roger
Race Director
Joined: May 2000
Posts: 12,712
Likes: 2,271
Re: Distributor Vacuum Advance Motor (RMS73)
Your ignition map is compromised for emissions, so if you don't have to be tested you can modify it.
For SHP engines the Echlin/NAPA VC1810 is best. It starts at about 4" and provides 16 crank degrees maximum at 8". You want all the vacuum advance in at idle, so be sure to connect it to a full manifold vacuum source, not a "ported" vacuum source that may not have vacuum at idle. If you have TCS, disable it so you have full manifold vacuum to the can at all operating conditions.
You should run a total to 36-38 initial plus centrifugal and you can also probably quicken up the centrifugal, which will give more low end torque. Not sure what your total centrifugal is, but if you have a spec you can use that to set the initial, however, the best way to set total WOT timing is to disconnect the vacuum can and use an accurate dial back timing light. Set the dial back at 36-38 then rev the engine until the timing mark on the balancer stops advancing and set it to zero on the tab. If the engine wants to detonate you can back off the initial a bit, or switch to mid grade or premium. With only 9:1 CR your engine was originally designed to run on regular unleading fuel.
Duke
For SHP engines the Echlin/NAPA VC1810 is best. It starts at about 4" and provides 16 crank degrees maximum at 8". You want all the vacuum advance in at idle, so be sure to connect it to a full manifold vacuum source, not a "ported" vacuum source that may not have vacuum at idle. If you have TCS, disable it so you have full manifold vacuum to the can at all operating conditions.
You should run a total to 36-38 initial plus centrifugal and you can also probably quicken up the centrifugal, which will give more low end torque. Not sure what your total centrifugal is, but if you have a spec you can use that to set the initial, however, the best way to set total WOT timing is to disconnect the vacuum can and use an accurate dial back timing light. Set the dial back at 36-38 then rev the engine until the timing mark on the balancer stops advancing and set it to zero on the tab. If the engine wants to detonate you can back off the initial a bit, or switch to mid grade or premium. With only 9:1 CR your engine was originally designed to run on regular unleading fuel.
Duke
