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Old 10-12-2001, 05:04 PM
airgrabber airgrabber is offline
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Join Date: Feb 2001
Location: Pewaukee,Wi
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Default Vacuum advance and tuning

I'm confused about the operation of the vacuum advance. I've seen it capped off on alot of street/strip cars and I've seen it hooked up on some others. What exactly is it's purpose and would I benefit more by having it connected or capped off. What is the best procedure to set the timing.I also do not understand what is meant by total advance. I read in a mopar book 1 time that you should set the timing at 32degrees with the hose disconested & then re-connect and dial in total advance @ the same RPM. Could someone please help me out here?
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Old 10-12-2001, 06:45 PM
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Glen440 Glen440 is offline
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The reason you see cars at the track with it plugged is because there is no vacuum at wide open throttle. It is used for better mileage on the street. You plug it and you set total advance by reving your engine till you get no more mechanicle advance and set it at that rpm. Then you set vacuum advance the same way with it hooked up. Its usually around 50 degrees. Its adjustable with an allen head screw that you get through the vacuum port.
You have to play with it cause too much advance on a high comp engine will make it ping. I just unhook it cause the engine I find surges with lumpy cams. I think it must be an uneven vacuum signal.
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Old 10-13-2001, 12:44 AM
shannon shannon is offline
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The vacume advance works only at part throttle. It is designed to work at part throttle because the cylinder pressures are lower at part thottle (less throttle = less air = less pressure). It takes more advance to set off a cylinder for the most effiency when the cylinder doesent have a lot of fuel and air. When the throtte is opened up all the way, more air =more pressure = more heat, requires less advance. To set your timing, unplug the advance and rev the engine to 2500rpm, set the timing at around 35 degrees. Plug in the advance and drive it . If it doesent ping your ok, if it does, adjust it with the allen screw (inside of the hole where the hose plugs in). I used to have a low comp 318. It would foul the pulgs without the advance if I'd let it idel for a while. Pluged in the advance and she ran like a timex.
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