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Forums->Hot Heads Tech Talk->Vacuum advance on 392

oldboy
Vacuum advance on 392


Hello,
Hey guys, i have a 392 with an Msd distributor, edelbrock carburetor.
Had some issues with the advance stop a few years back, one of you were helpful and guided me towards replacing the stop which cured the pinging i was getting under heavy throttle.
Recently i was pulling the car out after our long northeast winter and noticed that the vacuum advance is not hooked up.
Should i connect it to the carb, and will i get any better performance? Leave it be?
Advantages/disadvantages?
Thanks for any thoughts from you well versed members of the early hemis.Thanks Russ
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on: Thu 15 of Mar, 2018 [15:10 UTC] reads: 2525

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oldboy
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Re: Vacuum advance on 392
on: Sat 17 of Mar, 2018 [12:53 UTC] score: 0.00
> Hello,
Thanks Dave. I will read that article. Sounds like full vacuum is the way to go. Curious that the machine shop said use ported vacuum, but yes this car runs hot.
Appreciate the reply.
(Btw that lean burn example was just that , an example . Maybe not a ggod one. That car runs pertronix and vacuum advance.
works well and makes a world of difference with vacuum connected.)

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hemistude
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Re: Vacuum advance on 392
on: Fri 16 of Mar, 2018 [14:07 UTC] score: 0.00
Hey Russ,

Here's a great article that will help you understand the importance/influence of vacuum advance as well as giving a great overview of how all aspects of a distributor's timing control.

http://www.superchevy.com/how-to/additional-tech/1601-everything-you-wanted-to-know-about-vacuum-advance-and-ignition-timing/

You'll have to copy and paste the link into your browser since this site doesn't allow hyperlinks.

BTW, Lean Burn engines didn't have vacuum distributor advance. They DID, however, have a vacuum signal hose going to the crude computer board that was mounted in the air cleaner/hose system. I think it probably was ported to a MAP sensor that was part of the timing control. Vacuum didn't directly and immediately influence the timing directly like a true vacuum advance does.

I personally favor full vacuum to the distributor due to the reasons mentioned in the article. Ported Vacuum was only introduced in the early 60's as a way to reduce emissions and the result was a compromise to engine performance and efficiency. It, by design, raises idle temperature significantly too. Anyone having temperature issues while idling or "putting" around would be well served to study up on full vacuum advance.

Good luck. Dave

author message
Jack
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Re: Vacuum advance on 392
on: Thu 15 of Mar, 2018 [16:12 UTC] score: 0.00
I would think a little experimenting would be in order.
Both with your timing light and road tests.

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oldboy
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Re: Vacuum advance on 392
on: Thu 15 of Mar, 2018 [16:09 UTC] score: 0.00

Hi George,
thanks for speedy reply. Yes but it is there, and has not been connected , what IS the benifit of using it? Besides possible gas mileage?
Will it pull better? Faster acceleration? All joking aside my early slant six had a "lean burn" ignition, and i can truthfully say the car runs better without it. That was a factory design that belonged there too. Albeit for a different reason.

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George
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Re: Re: Vacuum advance on 392
on: Fri 16 of Mar, 2018 [02:26 UTC] score: 0.00
>
> Hi George,
> thanks for speedy reply. Yes but it is there, and has not been connected , what IS the benifit of using it? Besides possible gas mileage?
> Will it pull better? Faster acceleration? All joking aside my early slant six had a "lean burn" ignition, and i can truthfully say the car runs better without it. That was a factory design that belonged there too. Albeit for a different reason.

Engine performs better with an advance that is working properly for the application. Have been numerous reports of having to recurve the Mopar Performance dizzys.

author message
George
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Re: Vacuum advance on 392
on: Thu 15 of Mar, 2018 [15:50 UTC] score: 0.00
If it wasn't good it wouldn't be on there....


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