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- Jul 12, 2011
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- Down South
As rpm increases, the amount of ignition lead required drops so let that guide you through your vacuum choices, lol.
but you'll need to adjust your final initial timing differently for eachVacuum or ported? Use whichever you like. The only difference between them is at idle, above idle they are the same.
Correct. I'm talking about at idle, depending on manifold or PV. If instead, after connecting MV, you just lower your idle speed, now you've possibly messed up your carb tune.Nope. They are the same. Once the throttle plate opens the vacuum signal is the same.
Ported advance is the same as advancing the timing to what a light would show on the balancer, as soon as you floor it it goes back to where the hose was off, till centrifugal took over. *** backward all around.So I think have read or watched 20+ articles on the ported vs. manifold distribution advance topic. In conclusion for a 67 R/T 440 4sp with a very mild
hop-up to the engine (aluminum intake, 1-up cam, Edel Performer, stock heads 10:1, stock manifolds, etc.)
1 - earlier AFBs including the original one for this car (which I have) had only a ported vacuum hookup, that must mean something as it was engineered that way
2 - Edelbrock says to hook non-emissions cars (like my 67 R/T) to the manifold vacuum for a 750cfm Performer like on the car currently. It has both outputs.
--> end result, play around with it and see which you like.
For anyone who cares, I will do some "seat of the pants" testing with different initial timings, and put observations in this thread. Once I solve the current
What I was saying, Visard said “55 degrees at idle”, under accelation no vacuum advance (that I know of) can drop to a degree (say 15 degrees) that won’t spark knock. I have to disagree on the last part of what you said. Why have high initial advance and then after pushing pedal to floor the vacuum drops to nothing and so does advance advantage? Better way, I’d to set initial at 36, port the vacuum to another 20, THEN when the vacuum drops you’re back to initial. Duel pickups in distributor would allow start-run. Done all the time on crank trigger type system.Post #29. The VA in this case is only dropping 14*, not 40*. I am unaware of any VA unit that adds 40*. 30* is the highest I have seen.
I remember reading some expert, maybe Eberg, saying like you said. Try both, and see what it likes.Frankly, being a tach drive no vacuum distributor user, I don't understand the conundrum. Only two ways, ported or manifold vacuum. Try it both ways, stick with the one that works best for you. DONE! (What is so freakin hard?)
Now, if you're talkin pinion snubbers and pinion angle.......
I will never understand how Ehernberg remembers or has access to so much. I hope he outlives me.I remember reading some expert, maybe Eberg, saying like you said. Try both, and see what it likes.
This is really good advice if you want to run manifold vacuum with a big cam and a 4 speed, also works well with automatics with loose converters. With big cams and tight converters you may want to try ported and a lot of initial. If you can't get 10 -12" of vacuum at idle in gear then manifold vacuum will be difficult to make run well with an automatic, with the currently available vacuum cans anyway.Engines with big cams that idle high can benefit most from manifold vacuum. It raises the idle speed without opening the throttle plates and exposing to much of the transition slot. This type of engine will also require a quick acting mechanical advance. So quick that as soon as rpms come up and vacuum goes away the mechanical advance us already stepping up and raising the timing.
So I think have read or watched 20+ articles on the ported vs. manifold distribution advance topic. In conclusion for a 67 R/T 440 4sp with a very mild
hop-up to the engine (aluminum intake, 1-up cam, Edel Performer, stock heads 10:1, stock manifolds, etc………..