Vacuum advance dist. for Model A

M

mcgarrett

Well-known member
Is anyone making or modifying a distributor for Model A engines that incorporate vacuum advance? I know about the Rex-a-co centrifugal advance unit, but it's not vacuum controlled. Has anyone ever modified a distributor like the Bosch 009 for example that would work well in the Model A engine? Would there be any benefit especially when running high compression heads?
 
I have read on here somewhere that a 70's (?) Honda distributor can be modified to fit the Model A.
 
you have to be careful with 70s distributors, some have vacuum retard.
some Subaru ones also could be used, all will require modifications to the advance curve
 

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I run a modified Honda civic points distributor (Hitachi 1975) with mechanical and vacuum advance. It performs wonderfully. Set up 2 years ago and haven't touched it since. Bullet proof.

I made all the modifications myself and do not know of anyone who supplies them for a Model A. The Honda distributors of that era are becoming harder to find.
 
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For a dist with vacuum advance you will need a carb wit a port for that, most vacuum dists don't use manifold vacuum. I doubt if there would be enough improvement to notice?
 
Jim Brierley said:
For a dist with vacuum advance you will need a carb wit a port for that, most vacuum dists don't use manifold vacuum. I doubt if there would be enough improvement to notice?
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Jim, In my case, I am running a Weber 32/36 with the vacuum port. Hooked the vacuum line from the distributor to the vacuum port on the carb. Works great for cruising, improves mileage. When more throttle is needed, you get vacuum retard. :)
 
#3 cylinder on old VWs ran 3 degrees of retard. That cylinder was shrouded by the oil cooler and they retarded the spark to keep it a little cooler. The Porsche 356/912 distributors had evenly spaced distributor cams.
The air cooled VW used a clockwise rotation distributor and the Model A is CCW.
 
I'm using a Rover 4cyl. dist. with vacuum advance. You can get them with points or
electronic ignition. Easy conversion.
Carburetor is one of the new Stromberg 97's with a vacuum port.
 
Dodge said:
I'm using a Rover 4cyl. dist. with vacuum advance. You can get them with points or
electronic ignition. Easy conversion.
Carburetor is one of the new Stromberg 97's with a vacuum port.
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Isn't that a downdraft, with 3 mounting holes to the manifold? Where did you get that?
 
Gene F said:
Does the rotation direction matter?
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Yea, the advance is backwards. You can change the Bosch 009 ( A centrifugal advance only distributer) by revirsing the way the weights advance.
Also the 009 type does not retard the #3 firing, that only happens with the early factory used VW stuff.
The 009 and 050 Bosch can be made to work well but again there only centrifugal advance not what the OP is looking for
 
I've been running a modified Nissan distributor on my Burtz engine and love it. It was done by "Performance Ignition" in Nunawading, Melbourne. I have used them before and been impressed each time. A bonus for you guys is that the exchange rate works FOR you but unfortunately, AGAINST us.
 
ModelA29 said:
#3 cylinder on old VWs ran 3 degrees of retard. That cylinder was shrouded by the oil cooler and they retarded the spark to keep it a little cooler. The Porsche 356/912 distributors had evenly spaced distributor cams.
The air cooled VW used a clockwise rotation distributor and the Model A is CCW.
Click to expand...

This is not correct as you stated. VW did this only for a handful of years, and not for the reason you stated. It only occurred in the 69-72 VW’s that were 1600cc before they went to the doghouse cooler.

This didn’t happen with the 356/912 distributors. Those cars used different distributors. The distributor rotation has nothing to do with any of this.
 
Phil Brown said:
Yea, the advance is backwards. You can change the Bosch 009 ( A centrifugal advance only distributer) by revirsing the way the weights advance.
Also the 009 type does not retard the #3 firing, that only happens with the early factory used VW stuff.
The 009 and 050 Bosch can be made to work well but again there only centrifugal advance not what the OP is looking for
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I wouldn’t bring the 009 into this discussion. It’s a centrifugal advance distributor but needs a carb that is properly matched. 009’s are very particular.

Most carburetors are designed for distributor advance, mechanical, centrifugal or manual. It’s best to match the distributor advance mechanism to the carb advance. Just because it fits doesn’t mean it’s appropriate.
 
Hitman said:
Most carburetors are designed for distributor advance, mechanical, centrifugal or manual. It’s best to match the distributor advance mechanism to the carb advance. Just because it fits doesn’t mean it’s appropriate.
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Pardon my ignorance, but what is carb advance?
 
I never understood the need for vacuum advance until I researched it yesterday after seeing this thread. I always figured an engine develops its highest vacuum when the throttle is closed or slightly opened, and wouldn't need advance under these conditions. But I read that when cruising at a steady speed and only a little load, the throttle is only partly opened, increasing vacuum, and also the fuel/air charge going into the cylinders is restricted by the throttle. This less dense charge of fuel/air takes more time to burn because, well, it's less dense. And because it takes longer to burn you need the spark to occur earlier. Fascinating.
 
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