Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1818703
05/04/15 07:04 PM
05/04/15 07:04 PM
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Supercuda
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Stock, there is no vacuum advance at idle, either. One time I accidentally hooked up vacuum advance at idle and I could not get my idle speed to settle down properly. Once I figured out what I had done and fixed it things were fine.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1818730
05/04/15 07:35 PM
05/04/15 07:35 PM
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Posts: 36,040 Lincoln Nebraska
RapidRobert
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16/36/all in at 3K ain't outrageous. I'd start by plugging the can in to ported & if it only pings at WOT I'd slow the curve with a slightly heavier spring on one side. Best would be a bit more octane. If you're right on the edge a next colder plug MAY help. Experiment with manifold too & you'll for sure need to shorten the slots. With manifold I'd set the initial with the vacuum gauge method then shorten the slots to 35/36 then a heavy enough spring combo to stay just under the pinging point at WOT up thru the gears on your hottest/driest day. Best is more octane but most individuals are set in stone where they are at with that choice. Bottom line NO pinging allowed at any time.
live every 24 hour block of time like it's your last day on earth
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Re: Distributor Vacuum - Use or Don't Use?
[Re: RapidRobert]
#1818752
05/04/15 07:56 PM
05/04/15 07:56 PM
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Posts: 1,526 North Carolina
cjskotni
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16/36/all in at 3K ain't outrageous. I'd start by plugging the can in to ported & if it only pings at WOT I'd slow the curve with a slightly heavier spring on one side. Best would be a bit more octane. If you're right on the edge a next colder plug MAY help. Experiment with manifold too & you'll for sure need to shorten the slots. With manifold I'd set the initial with the vacuum gauge method then shorten the slots to 35/36 then a heavy enough spring combo to stay just under the pinging point at WOT up thru the gears on your hottest/driest day. Best is more octane but most individuals are set in stone where they are at with that choice. Bottom line NO pinging allowed at any time. What I am trying to do is clean up my idle/part throttle some so wouldn't I want to skip the ported vacuum as it has no signal at idle? I know this won't fix the WOT pinging by itself as it can only advance the timing. What I was envisioning is maybe I could dial back the distributor to maybe 10-12* base timing and use the vacuum advance to keep the advance up at idle-part throttle but drop off at WOT which would then top out at 30-32* which might help the pinging? Does this make sense or am I missing something??
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Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1818770
05/04/15 08:08 PM
05/04/15 08:08 PM
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Joined: Oct 2007
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hooziewhatsit
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First, I'd get the pinging situation solved. Either limit the total, or reduce the initial. It should never ping, and adding the vac advance won't do anything to change it.
Two schools of thought on ported vs manifold for the distributor:
Ported: No vacuum at idle. You can run a high(er) initial timing, but too high can cause kickback/starting issues. Easier to tune, since you know the timing won't change between neutral and drive (at least, it shouldn't).
Manifold: Vacuum at idle adds timing, but only after the engine is running, so starting won't be fighting a high initial. Vacuum drops out at WOT, which is fine. You MUST make sure that your idle and drive vacuum levels are higher than the vacuum the can needs to provide the advance, otherwise your idle will bounce all over the place.
What you're envisioning should work just fine, presuming you have enough vacuum to make sure the can is always advanced at idle/in drive.
Last edited by hooziewhatsit; 05/04/15 08:09 PM.
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Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1818780
05/04/15 08:16 PM
05/04/15 08:16 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
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what I would do is set the initial with the vac gauge method then shorten the slots to get the std total (which is initial+slots) for your eng type (ie 35-SB) then springs then plugin/adj the can. this would be for ported. then I would hook the can to manifold and same vac gauge method for initial then shorten the slots for the same correct (for your eng) total then springs & see which one works the best for you. there may be a better approach to this as modding the slots ain't easy & I have no exp with manifold but what I've read up on it, it does sound appealling/worth doing. first, more info on whats going on with cleaning up the idle/part throttle response problem. #1 dont allow it to ping! you want close to it for max power and or economy but never over that line
live every 24 hour block of time like it's your last day on earth
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Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1819222
05/05/15 10:50 AM
05/05/15 10:50 AM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
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I'm wondering if I role the timing back maybe 2* to 14* base (34 total), then that might cure the pinging issue. However, I'm wondering what the vacuum advance will do to the idle advance...if it will be too far advanced or not. (1) that's an excellent plan/easy to do/easily reverseable, try 2 or 3 degrees (2) plugging the can in to manifold will definitely require resetting the initial with the dist housing as a can with 7 stamped on the arm will add 14 initial & (as said/VG point) in regards to the idle vac you'd want a can that maxes out at a in hg number lower than your idle in hg reading
live every 24 hour block of time like it's your last day on earth
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Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1819267
05/05/15 12:10 PM
05/05/15 12:10 PM
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MikeyT
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I would say get the pinging fixed quickly and then go from there
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Re: Distributor Vacuum - Use or Don't Use?
[Re: Twostick]
#1819424
05/05/15 04:04 PM
05/05/15 04:04 PM
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Joined: Jul 2007
Posts: 1,526 North Carolina
cjskotni
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If that dist is the Mallory built MP unit, you can adjust the advance. The procedure should be in the Tech Archive.
No welding required.
Kevin I just read the tech archives and see this: "Although not discussed in MP's instructions, the mechanical advance is a Mallory adjustable YH type (same as used in most Mallory distributors). It is fully adjustable from zero (locked out) to 28 degrees. We set them at 28 degrees when we ship them to MP. All you need to adjust (or lock out) the advance is a Torx driver to loosen two button head screws. " How do I know if mine is adjustable? Also where do these torx screws reside? **EDIT** I think I got this figured out. If my distributor has this, I will need a set of the keys to set the gaps between those tabs. So do most people with performance STREET motors run vacuum advance or leave it disconnected?
Last edited by cjskotni; 05/05/15 05:15 PM.
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Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1819482
05/05/15 05:19 PM
05/05/15 05:19 PM
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Joined: Oct 2007
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hooziewhatsit
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So do most people with performance STREET motors run vacuum advance or leave it disconnected? If you're running on the street, there's no reason not to run vac advance. Better mileage and burn during cruise for one reason. If the car is only used on the strip, I wouldn't use vac advance. Why? On the strip, the car only ever sees WOT, at which point the vac advance is inactive. So may as well not have it at all.
If you ever find yourself in a fair fight, your tactics suck.
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Re: Distributor Vacuum - Use or Don't Use?
[Re: hooziewhatsit]
#1819505
05/05/15 06:01 PM
05/05/15 06:01 PM
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Joined: Jul 2007
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cjskotni
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If you're running on the street, there's no reason not to run vac advance. I am worried about having too much timing at idle if I use manifold vacuum. Any idea of a ballpark of how much is too much for an engine combo like mine? I can tell it wants more timing at idle as when I advance it the idle picks up and feel stronger but I have been restricted by the total timing.
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Re: Distributor Vacuum - Use or Don't Use?
[Re: cjskotni]
#1819514
05/05/15 06:17 PM
05/05/15 06:17 PM
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Joined: Jan 2003
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dogdays
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It seems like you know what you're doing, or at least have an idea.
Your idea to use a limited mechanical advance with the vacuum advance providing extra at idle is interesting and it could work. Years ago I was convinced that manifold vacuum was the only way to go. I have moderated some, but your idea is sound, unless you develop a bog right off idle when you put your foot down, because advance will drop from 20 to 6 degrees. It's worth a try.
Mazda runs very high compression by limiting heat input into the intake charge. The cooler the intake manifold, the cooler the air sucked through the filter, the more the engine will like it. What I didn't expect is they found that the exhaust residual could also add heat, so on their Skyactiv engines, the exhaust manifold is like a header. Scavenging gets the hot air out.
Points to ponder, R.
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Re: Distributor Vacuum - Use or Don't Use?
[Re: Moparlar]
#1819627
05/05/15 09:03 PM
05/05/15 09:03 PM
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Joined: Nov 2007
Posts: 21,825 Kirkland, Washington
Pacnorthcuda
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Im missing something here, Why is there no ported vacuum an WOT. I would think that is where there would be the highest ported vacuum as you have the most air flow through the Venturi where ported vacuum comes is created so to speak. Because there is very little vacuum present ANYWHERE when your butterflies are wide open. The "ported" vacuum exists off ide, and part throttle conditions. that way vacuum advance exists only at part throttle conditions, by design.
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