Re: [FWDLK] Vacuum Advance Question

From a mechanical point of view, all these vacuum advances will fit any V8 distributor. But there are serious differences. The amount of travel in the different P/N advance diaphragms varies from 8 to 30 engine degrees. The replaceable springs have some that are 4 times stiffer than others. I have made a study of the 55 – 57 Mopars. Data is all over the map.

If too much vacuum advance is used, the engine will be over-advanced and probably pinging all the time. If too little is used, gas mileage will be way down.

In general, engines with little mechanical advance get a lot of vacuum advance. DeSotos are typical of these. Engines with a lot of mechanical advance get a smaller vacuum advance. Performance engines are typical of these.

For instance, a 56 Dodge 270 Poly has 36 degrees of total mechanical advance and 8 degrees vacuum. Using a 30 degree vacuum chamber will over-advance this engine by 22 degrees! A 57 DeSoto Firedome has a total mechanical advance of 26 degrees and a 30 degree vacuum advance. Using an 8 degree vacuum chamber will under-advance this engine by 22 degrees!

I my opinion, using the correct advance diaphragm, or at least one near the original degrees travel, is very important.

Dave Homstad

56 Dodge D500

-----Original Message-----
From: Forward Look Mopar Discussion List [mailto:L-FORWARDLOOK@xxxxxxxxxxxxx]On Behalf Of jrawa@xxxxxxx
Sent: Monday, April 13, 2009 11:58 AM
To: L-FORWARDLOOK@xxxxxxxxxxxxx
Subject: Re: [FWDLK] Vacuum Advance Question

theyre all the same but different... from a replacement standpoint [mechanic's ideal that is] one size fits all... but 2bbl and 4bbl apps had different spring rates in relation to in/Hg vacuum to advance, as in more of an aggressive advance rate... and dual point distributors for dual quad motors were also unique... and there are variations there, of course there isthe bigger b/rb difference, but a sonoram 413 advance characteristics are different than say, a 350 commando or inline dual quad 413 H motor...
BUT at the end of the day... you wont feel the difference.. at least not enough to worry about... AND if you're replacing an advance pod, chances are yours isnt working--- so ANY added advance will feel much better!

-----Original Message-----
From: Ron Waters <ronbo97@xxxxxxxxxxx>
To: L-FORWARDLOOK@xxxxxxxxxxxxx
Sent: Mon, 13 Apr 2009 12:21 pm
Subject: [FWDLK] Vacuum Advance Question

Hi Gang -

Looking thru the parts book, it seems like every distributor has their own unique vacuum advance. Yet when I look on ebay, vacuum advances are listed as fitting 57-61 Plymouth and Dodge with 318 and without power pak. Kind of a 'one size fits all' thing. Will these aftermarket guys work, or would I have to find the exact part number that fits my distributor, assuming that I would have to replace the vacuum advance.

Thanks,

Ron
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