Engine builder recommends capping off vacuum advance
- Thread starter nicanor
- Start date
mcmopar
Well-Known Member
I wouldn't but that is just me. I run mine at around 30-32 degrees of centrifugal advance and then set the screw adjustment in the distributor vacuum advance pod to 8 turns from fully closed (about half-way between fully closed and fully on). I then hook up the vacuum advance. Capping off the vacuum advance is great for maximum performance but the vacuum system was for better street manners. If you want all-out power cap it off and set your timing to 36 degrees of centrifugal advance at around 2400 rpm but be advised - it may be a bit difficult to crank when starting - especially with a stock starter.
SomeCarGuy
Well-Known Member
Some guys say that vac advance causes a surge. A little tuning may fix that. No reason to pay for extra gas if you don't have to. I would get the engine broke in w/o it and then play around with it once all the other bugs are sorted out.
A31PKG
Well-Known Member
I've posted this before (I think) but it's worth another look.... Sometimes these cars like vacuum advance, sometimes not. It is largely dependent on the distributor advance curve, weights & springs etc. It also depends on the vacuum your engine makes, and at what RPM. For example, a stock 383 may function as the engineers designed it, but adding a higher lift/longer duration cam will usually cause a tweak in the vacuum that can adversely affect vacuum advance - the car just won't "like" it anymore. It may at that point run better with it capped. I always start with a base timing adjustment without v.a. and see how the car runs. Then re-connect and note performance. You may find that it makes more power, but pings... run higher octane, try again. Sometimes fine tuning the timing is in order. Too much up or down, though, can affect how the car cranks over, engine temps, performance, hesitation, etc. Your guy may be right in this case. It's all about trial and error. In the absence of a dyno, this is what I do, and it usually works every time: Plug the v.a. hose, connect vacuum guage to manifold source (below throttle plate), start and warm up engine, allow to idle, rotate distributor until you reach your highest steady vacuum reading, back off (retard) about 2" and lock it down. Take it for a drive and see how it does. Then re-connect the v.a. and drive again. If it's better, great, if not leave it alone. This will give you a baseline from which you can fine tune further with timing, weights, springs, & v.a. diaphram adjustments.
moparchris
Well-Known Member
i never run a vacuum advance. It probably does increase mileage but not worth the hassle and chance of detonation under partial engine load. Its mostly an emissions device. Ditch it. :cents: