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Vacuum Advance Modules
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Powerflite
Posted 2019-06-04 7:17 PM (#582932)
Subject: Vacuum Advance Modules



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I am trying to figure out what is the best vacuum advance module to use with an electronic aluminum distributor for a small block in our forwardlook cars. There are numerous versions and specs for them, but these are the ones I was able to find. I am leaning towards the VC189 since it comes on over a wider range and has a higher advance amount. The 189 also mounts at a pivot point that is closer to the center so the total movement is less. Maybe this is good to make it last longer? The VC-155 for the older points distributors also looks good, but I'm not certain it is compatible with the electronic distributor pivot points. The VC-168 was used for many of the early 70's muscle car 340 & 318 motors but comes on quicker and to a lower value. Any suggestions?



(Vacuum Advance Modules.jpg)



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58coupe
Posted 2019-06-05 10:31 AM (#582955 - in reply to #582932)
Subject: Re: Vacuum Advance Modules



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This depends a lot on how you build your engine, compression ratio, cam etc. You know this only effects your part throttle cruise and you don't want your engine "pinging" from too much advance. VC173 has less total but works with less vacuum on the higher performance engines. Since few if any of us have access to an engine dyno, try one or two and see.
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Powerflite
Posted 2019-06-05 5:30 PM (#582977 - in reply to #582932)
Subject: Re: Vacuum Advance Modules



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That may be a good approach. Maybe I'll try two at opposite ends of the spectrum and see which one works best, and then figure out why.
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Powerflite
Posted 2019-06-05 6:12 PM (#582981 - in reply to #582932)
Subject: RE: Vacuum Advance Modules



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I made a plot of the advance created vs. the vacuum level for the different parts. In the cases where a range of values was given, I just picked the average value. This graphic representation is helpful to tell me that the VC189 and VC173 follow the same curve, just that the 189 continues on with more advance. It also shows that VC190 and VC155, are almost the same with the VC155 limiting the advance a little more. So if I were to test them out, I could make conclusions based on the curve position by comparing VC189 and VC168 since they are most different from each other, but have similar total advance amounts. Then I can compare VC 178 to VC189 to make a total advance comparison, keeping the curve approximately the same.

Edited by Powerflite 2019-06-05 6:13 PM




(Vacuum Advance Plot.jpg)



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58coupe
Posted 2019-06-06 10:19 AM (#583021 - in reply to #582932)
Subject: Re: Vacuum Advance Modules



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Are you going to play with the centrifugal advance also?
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Powerflite
Posted 2019-06-06 11:07 AM (#583024 - in reply to #582932)
Subject: Re: Vacuum Advance Modules



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Ideally, I would recurve the distributor to make it all match the motor's needs & vehicle weight etc. But the reality is that I am just looking for a general use vacuum advance that I can keep in stock and use as they die out on my cars. I don't even know which original distributors each motor is running as most of the tags are long gone on them. The advance recently died on my Coronet and I *believe* it had a VC190 in it. I replaced it with a VC168 just because I had it on hand. But it's hard to make a comparison between them because the old one was was dying on me.
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