Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - ported vacuum vs. manifold vacuum
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Old 06-12-2006, 10:19 PM
potts potts is offline
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You haven't indicated the type if dist. I've found many aftermarket perf dist are set up that way with a relatively small amount of mechanical advance. They expect that you have a longer duration cam and will run alot of initial advance.
One thing ported or manifold the initial timing is the same with the vac hose plugged. Manifold is fine for a cooler idle and simpler set up. It's stock on a 283.
I find that with any amount of cam duration, it makes the idle a pain cold and the engine wants to hunt (rev up and down). I prefer the ported. Take your maximum available mechanical advance in degrees and subtract that from 32. That should be your initial to start . If you get knocking in any med or heavy accelleration back off the initial 4 degrees at a time until it stops. Any light throttle knocking is the vac advance not backing off soon enough and requires an adjustable vac advance to get the vac pot to advance at a higher vac reading.

Rule of thumb : short duration cam or tall gears mechanical advance comes in slowly. all in at 3000

long duration cam or low gears ie 411/1. mechanical advance comes in quick .all in by 2000

good luck
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