Re: Manifold vacuum - try it!
[Re: Secret Chimp]
#1198235
03/17/12 04:10 PM
03/17/12 04:10 PM
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Joined: Jan 2003
Posts: 5,446 Indiana
YO7_A66
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master
Joined: Jan 2003
Posts: 5,446
Indiana
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I just had my first two test drives using manifold vacuum and the idle in D and the vacuum reading and idle rpm's were smoooth. The idle was lean at first but once I retuned the carb, the in D idle was excellent. Note: FBO vacuum advance dist.: 32 degrees in N and in D.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Manifold vacuum - try it!
[Re: can.al]
#1198238
03/17/12 10:48 PM
03/17/12 10:48 PM
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Joined: Oct 2007
Posts: 3,933 Oregon
hooziewhatsit
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Joined: Oct 2007
Posts: 3,933
Oregon
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Quote:
..with a large cam and lo manifold vac at idle, a mopar can will not advance properly and will just dither in and out and give an unstable idle. ..a replacement can that starts advancing at 2 or 3" below the idle vacuum is required.
I would agree with this. As long as your idle vacuum is a few inches above the vacuum needed for full advance, it should work just fine.
The trouble arises when your idle vacuum and can vacuum are the same (or close), then you get feedback loops that lead to a roaming idle.
edit: as long as your idle vacuum in drive is higher than the can vacuum, it should work just fine.
Last edited by hooziewhatsit; 03/18/12 12:18 AM.
If you ever find yourself in a fair fight, your tactics suck.
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Re: Manifold vacuum - try it!
[Re: hooziewhatsit]
#1198239
03/18/12 12:14 AM
03/18/12 12:14 AM
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Joined: Jan 2005
Posts: 3,344 Central TX
roe
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master
Joined: Jan 2005
Posts: 3,344
Central TX
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I was having similar issues with unsteady idle that was surging in D and N. Switching over to manifold vacuum at the suggestion of some guys here took care of that. Idle is now smooth and steady, and no more huge drop in rpm from N to D. I just have a stock replacement dizzy with pertronix though. I would like to learn how to adjust the advance curve with someones help in person though. I've seen it described many times on here but I like to be hands on with someone to guide me when doing stuff like this for the first time.
roe
1971 Plymouth Satellite 408/904 8 3/4 3.23 SG
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Re: Manifold vacuum - try it!
[Re: roe]
#1198240
03/18/12 12:23 PM
03/18/12 12:23 PM
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Joined: Jan 2003
Posts: 5,791 Hamilton, Ontario Canada
Magnum
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Joined: Jan 2003
Posts: 5,791
Hamilton, Ontario Canada
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So a few members have tried manifold vacuum advance.
Found an improvement in idle quality, tip in and mileage and the rest of you insist on telling us it will not work according to instructions from 40 years ago.
At light load, partial throttle. Mild engines will happily motor along at 40-50 deg of timing.
If it takes 9" to pull a typical cannister open. Who cares if the vacuum is fluctuating between 12-22. The can will not move.
69 Super Bee, 93 Mustang LX, 04 Allure Super
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Re: Manifold vacuum - try it!
[Re: pjc360]
#1198245
03/20/12 10:33 AM
03/20/12 10:33 AM
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Joined: Mar 2008
Posts: 5,746 Ontario, Canada
Dodgem
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Ontario, Canada
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Hooking to manifold vacuum just masks a problem but is a quick fix for people who lack the now how (like the guy at FBO) to get their idle timing to a place where it needs to be after performance changes. Vacuum advance was designed to pull extra timing on at highway cruise to give better gas mileage. If your using it improperly at idle you are not making proper use of it cruise. So going to manifold vacuum at idle you will be giving up some of the performance a motor could offer and will also not be getting all the gas mileage available. To most on hear the all the power a motor can deliver is not a Goal so my question is why the upgrades???
Last edited by Dodgem; 03/20/12 10:34 AM.
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Re: Manifold vacuum - try it!
[Re: 70VcodeCoronetRT]
#1198248
03/20/12 08:48 PM
03/20/12 08:48 PM
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Joined: Jul 2011
Posts: 819 Eugene, Oregon
Secret Chimp
OP
super stock
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OP
super stock
Joined: Jul 2011
Posts: 819
Eugene, Oregon
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Quote:
So does FBO recommend manifold vacuum with their distributors?
Yes, though they do things with the vacuum pots to make them hold idle correctly. People have had problems with flakey FBO ECUs in the past but I don't think anybody's ever complained about their distributors.
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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