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1967 Mustang Convertible
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Discussion Starter #1
So I have been playing with my Vacuum Advance since it has an adjustable vacuum canister. When I hook up my Pittsburgh Vacuum Kit to it and I start putting vacuum to the canister at idle, I get this output:

Screen Shot 2020-05-05 at 5.59.53 PM.png

So as you can see with my Initial setting to 12 deg, I can be up to 38deg with 20 hg which I saw coming from my ported
vacuum but if I am at 3000rpm and my timing is 34 plus 26deg I could be at 60???

I looked at the MSD Ready to Run Distributor and they have their vacuum doing the following:
Screen Shot 2020-05-05 at 5.41.53 PM.png



So I guess my question is has anyone else measured what their vacuum actually does? Not sure my test is valid since I am measuring at a standstill and not while driving the car. Just seems 26deg of vacuum advance is a lot, i might turn it down but I notice that MSD 12 hg gives 16 deg advance and mine 12.5hg gave me 19deg of advance. Is this just a try and feel kind of thing?
 

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Well, if you are willing to 'try and feel' for a whole day, maybe. You can get excellent results in an hour by using factory specifications. Here's the 289 4V specs-
753307
 

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Discussion Starter #3
Great I have never seen that, I will try to match my canister to that. Wow mine is advancing it way too much. But looking at the Cetrifugal advance that seems really low. SO if you have a max advance of 14 and start out at 12 you will only have 26deg total, seems really low when most Aluminum headed cars want 34-36 total and I though our stock 289 heads want more then that like 38-40 total timing?
 

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65 Fastback 289 4 spd, 65 convertible 5.0L 5 spd. 3.73 8.8
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So I have been playing with my Vacuum Advance since it has an adjustable vacuum canister. When I hook up my Pittsburgh Vacuum Kit to it and I start putting vacuum to the canister at idle, I get this output:

View attachment 753303
So as you can see with my Initial setting to 12 deg, I can be up to 38deg with 20 hg which I saw coming from my ported
vacuum but if I am at 3000rpm and my timing is 34 plus 26deg I could be at 60???

I looked at the MSD Ready to Run Distributor and they have their vacuum doing the following:
View attachment 753304


So I guess my question is has anyone else measured what their vacuum actually does? Not sure my test is valid since I am measuring at a standstill and not while driving the car. Just seems 26deg of vacuum advance is a lot, i might turn it down but I notice that MSD 12 hg gives 16 deg advance and mine 12.5hg gave me 19deg of advance. Is this just a try and feel kind of thing?
Some distributors had a rubber around the tab sticking up to prevent to much vacuum timing. Some of the dist. had the tab bent for less timing. No matter what set your base timing without vacuum at between 8-14 deg. and your total with mechanical, no vacuum should be 34-36 deg. then set your vacuum accordingly so you don't ping while cruising at 55. I don't like more then 15 deg. vacuum which would put you 40-51 deg. depending on how fast your mechanical comes in. I like to have my mechanical all in by 3000 rpms, but all of my engines are warmed over.
 

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Great I have never seen that, I will try to match my canister to that. Wow mine is advancing it way too much. But looking at the Cetrifugal advance that seems really low. SO if you have a max advance of 14 and start out at 12 you will only have 26deg total, seems really low when most Aluminum headed cars want 34-36 total and I though our stock 289 heads want more then that like 38-40 total timing?
Double the advance numbers in the chart for degrees at the crank.
 

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Discussion Starter #8
Double the advance numbers in the chart for degrees at the crank.
Ahh now that makes sense. So for Vacuum I want 16-22 at 20hg and I am at 26 so not crazy out of whack like I thought but still on the high side. I will shoot for 16 and work from there. Thanks for the info guys.
 

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Double the advance numbers in the chart for degrees at the crank.
^ ^ ^ Correct. The specifications shown are in DISTRIBUTOR degrees. Crankshaft degrees will be 2x those numbers. Also remember that pretty much the only time you'll have 20"hg of manifold vacuum at 3,000 rpm is during deceleration (closed throttle). That's when you want the additional advance as the fuel/air mixture will be extremely lean and will take much longer to burn completely.
 
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