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Old 05-18-2005, 10:03 PM
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new distributor...now what about vac advance?

ok, got a new dist(well, rebuilt). single points single vacuum advance made for a 68 mustang. The last 2 I had had big vacuum canisters with the port on top. This one vac canister is much much smaller and the port sticks straight out. Do I hook it to ported or full? Does it matter? I don't want to start a debate on which is better, but I thought a distributor was only optimized to use one or the other, not either, and the guy at Napa couldn't tell me which.

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Old 05-18-2005, 10:10 PM
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I've never heard of a dist being optimized for one or the other. It should be adjustable for how much advance you want though. It is a heavily debated subject. My opinion . . . give the engine what it wants. Try both and which ever provides you with the best running engine is the one I'd go with.
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Old 05-18-2005, 10:57 PM
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It goes to ported. That is what the advance feature is built for.
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Old 05-19-2005, 02:52 AM
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If you hook it to ported it will advance the timing as you accelerate which is the job of the mechanical weights.

It's hooks to constant so it can bring in more idle timing.

There is no debate, constant is the correct way to hook it up.
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Old 05-19-2005, 05:35 AM
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Quote:
Originally Posted by cuda66273

If you hook it to ported it will advance the timing as you accelerate which is the job of the mechanical weights.

It's hooks to constant so it can bring in more idle timing.

There is no debate, constant is the correct way to hook it up.
If a vacuum cannister is hooked to manifold vacuum, you will experience the full advance of the designed vacuum advance at idle. As manifold vacuum decreases with speed, the vacuum advance feature lessens and the mechanical advance takes over.

By doing it your way, there is no need for vacuum advance. Disable it and dial in more initial advance.

Why do you think it was assembled with ported vacuum?
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Old 05-19-2005, 06:10 AM
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"Ported" and "constant" are they not the same ?
The distributor should be connected to the "timed port" so that the vacuum advance is actuated during the transition from idle, no advance, to mechanical.There is a time when the weights will not be spinning fast enough to overcome the springs.
Why should the initial timing be set with the vacuum advance disconnected
only to be connected to port which will activate the vacuum advance at idle ?
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Old 05-19-2005, 07:29 AM
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Timing

My take on this,,,,

Forget about what gm ford and chevy did with the vacuum advance,,, it was about a different deal then us hot-rodders are doing.... This is all from the hot-rod point of view

Let's look at the system.

First, with the advance un-hooked,
The mechanical timing will need be set to the initial and total needed for each engine. A performance street engine will need something different then a race engine. You did not give us your application so i will guess at a combo... The theory works the same for the different engines you just need to find the correct numbers....

Say you find your engine works best with 12 degrees initial and 38 total timing. You will need to get your distributor set up so that you have 26 degrees of advance in it. Once you get that all worked out then you can go to the vacuum advance and start tuning that. I hook it to manifold vacuum. This will give you additional initial timing that will aid in the idle quality. It will drop out when the engine is off so when you crank it to start it there will not be any problems from to much initial timing. Also when you wack the throttle it will drop out also and the engine will rely on the mechanical advance. Remember we got that all worked out first so there will be no suprises because of heavy springs or sticking weights...... The amount of vacuum advance needs worked out just like the mechanical. But i am going to guess at this also and say you limit your vacuum to 10 degrees.

So now what you have with the system all in tack is a cranking timing of 12 degrees when the engine fires you have a idle timing of 22 degrees ( 12 initial and 10 in the vacuum can) A total timing at wot of 38 degrees and a crusie timing of 48 degrees ( 12 initial, 26 distributor, and 10 in the can) Most engine will handle alot of total timing at cruise because there is no load on them. With this set up if you are cruising along and wack it the vacuum advance will drop out and you will have just the total mechaincal timing....

I have operated this system on near stock to some very modifyed engines and it works perfect....

Remember the numbers are just numbers i use for examples.... they are not the numbers to use for your set-up. If you give use some idea of your combo we might be able to give you a good starting base....

One thing i have found on all the ford distributors i have worked on is they have a excessive amout of mechanical advance and you will need to take the distributor apart and limit this......

Keith
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Old 05-19-2005, 11:28 AM
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Like I said . . . opinions on either side . . . bottom line is give the engine what it wants. What setup FEELS best to you and your engine?
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Old 05-19-2005, 11:30 AM
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Quote:
=malcWhy should the initial timing be set with the vacuum advance disconnected
only to be connected to port which will activate the vacuum advance at idle ?
For the same reason its set by bypassing the Spark controller on electronically controlled timing cars. So that you know and have set your BASE number uninterrupted from other sources. As soon as I plug the computer back in (which would be the equivilant of the vacuum canister) my timing jumps back to about 20. It builds on whatever your initial setting is.
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Old 05-19-2005, 11:50 AM
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Okay I am going to try it, to see what happens.
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Old 05-19-2005, 10:13 PM
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i installed it and played with timing. The best timing(that that didn't miss thrroughout the rpm range) but idled kinda low for my liking. So I hooked into full manifold vacuum. Runs well. Now I still have this problem that my engine lugs WAY down when put into gear(will actually stall if idle isn't high enough), guess that isn't related.
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Old 05-19-2005, 10:45 PM
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What did you set your initial timing at? Have you adjusted your idle settings on your carb since setting your timing?
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Old 05-20-2005, 12:02 AM
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that i'm not sure about exactly. I had someone set it to 8 degrees by the marks on it, but that was way too advanced so i'm assuming the marks are wrong. Right now it's more or less timed by ear with a little emphasis on the retarded side so it's not pinging until I can make it more official. On the ported port, I couldn't ever get it to rev without a little missing unless the timing was set too low to have a decent idle...on full vacuum it works well with only a slight little wiggle in the high rpms, but that is most likely due to it being points. Ah this brings another question. To set the idle adjustments on the carb, that should be done WITH vacuum hooked up to get accurate timing correct?
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Old 02-17-2009, 08:00 PM
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Quote:
Originally Posted by woedend
that i'm not sure about exactly. I had someone set it to 8 degrees by the marks on it, but that was way too advanced so i'm assuming the marks are wrong. Right now it's more or less timed by ear with a little emphasis on the retarded side so it's not pinging until I can make it more official. On the ported port, I couldn't ever get it to rev without a little missing unless the timing was set too low to have a decent idle...on full vacuum it works well with only a slight little wiggle in the high rpms, but that is most likely due to it being points. Ah this brings another question. To set the idle adjustments on the carb, that should be done WITH vacuum hooked up to get accurate timing correct?
I put my engine on full vacuum and timed it with a vacuum gauge to top vacuum, then back about half an inch of vacuum, and mechanical advance with heavy springs on it, the only thing i noticed was a wiggle at about 4000 rpm, and found that the weights were sticking on the rotor, so I put some flat washers under the rotor, and it seemed to work good. The engine is a 383, and when timed with a gun, had like 26 deg at 800rpm
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Old 02-17-2009, 09:11 PM
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Quote:
Originally Posted by malc
Okay I am going to try it, to see what happens.
I'm sure you've had time to do this between now and 4 YEARS ago when this was posted? Are you still or firm believer in ported or did you convert to manifold?
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