ported vacuum

demingboy

demingboy

Member
So what I am trying to understand is why the stock distributer will not work when you change to a new manifold and carburetor. I am wanting to use the small 390 cfm holley carb.
The motor is a 1951 ford 239 . Will switch to the petronix electronic ignition, using their coil and the recommended wires to plugs. Will remain 6 volt.
What I am un sure of is why the difference in vacuum created by my stock manifold and carburetor is different from new installation.
I have the ability to use either ported or manifold vacuum for the advance on the distributor so I am a little confused.
Also might admit I am not the sharpest tack in the box lol.
 
Ported vs manifold vacuum is not the issue. The original carburetor is designed with ports above and below the throttle plates that proves the required vacuum to the original distributor. Only a carburetor specifically designed for the original distributor will work. If you want to switch to a different carburetor you need to switch out the distributor to something like the modified Chevy units which can be mechanical advance only or a combined mechanical vacuum unit. These units use manifold vacuum.
 
The 8BA distributor is 100% vacuum controlled, no mechanical adv at all. It's design
is for use with venturii vac from above the throttle plates of a single 94 style carb.
Change the carb away from the 94 design and the vac 'signal' from the carb to the
8BA distributor is lost or changed so as to ineffectuate advance characteristics. I
suppose if the carb you intend to use has a port above the throttle plates you
could try it....maybe it'll get you in the ball park.
Charlie ny
 
"Petejoe" on the H.A.M.B. just posted this link over there. I found it to be very informative. https://fordsix.com/ci/Loadomatic.html.

I think it should be required reading for all post '48 flathead owners ("Y"-blocks and sixes too).

I finally understand the whys and wherefores of the "spark valve" on the later carburetors.
 
Last edited:
Charlie ny said:
The 8BA distributor is 100% vacuum controlled, no mechanical adv at all. It's design
is for use with venturii vac from above the throttle plates of a single 94 style carb.
Change the carb away from the 94 design and the vac 'signal' from the carb to the
8BA distributor is lost or changed so as to ineffectuate advance characteristics. I
suppose if the carb you intend to use has a port above the throttle plates you
could try it....maybe it'll get you in the ball park.
Charlie ny
Click to expand...

The ported spark on a 4 barrel does not replicate the venturi vacuum signal on a 94.
 
GREAT article.
Now I know why my ‘51 F1 accelerates so crappy and gets 11 miles per gallon on a good day.
I would say there are three ways to correct a giant flawed system.
1. Change to a different engine
2. Get the GM distributor installed pronto ( best option)
3. Rig up a manual spark advance (easiest and cheapest).
 
How about option 4 : Get the stock system up to snuff and working correctly?

I ran the stock loadamatic/carburetor setup in my '51 for almost 30 years when I had a stock engine. It worked just fine.
 
Just my 2 cents... If a ford distributor is Ventura vacumn only and a small block Chevy distributor vacuum advance is manifold vacuum, why can't you put a Chevy vacuum advance on an 8 ba distributor to make manifold vacuum usable? Better yet, why can't the internals of a Chevy distributor be made to fit inside the 8ba distributor for mechanical advance and eliminate the machining of the distributor, cutting of the shaft, making a hold down, etc., etc, to use on an 8ba and still have an all ford distributor?
 
BRU said:
Just my 2 cents... If a ford distributor is Ventura vacumn only and a small block Chevy distributor vacuum advance is manifold vacuum, why can't you put a Chevy vacuum advance on an 8 ba distributor to make manifold vacuum usable? Better yet, why can't the internals of a Chevy distributor be made to fit inside the 8ba distributor for mechanical advance and eliminate the machining of the distributor, cutting of the shaft, making a hold down, etc., etc, to use on an 8ba and still have an all ford distributor?
Click to expand...

Much easier to just use the Chevy distributor, much easier. You can also modify some Chrysler models.
 
BRU said:
Just my 2 cents... If a ford distributor is Ventura vacumn only and a small block Chevy distributor vacuum advance is manifold vacuum, why can't you put a Chevy vacuum advance on an 8 ba distributor to make manifold vacuum usable? Better yet, why can't the internals of a Chevy distributor be made to fit inside the 8ba distributor for mechanical advance and eliminate the machining of the distributor, cutting of the shaft, making a hold down, etc., etc, to use on an 8ba and still have an all ford distributor?
Click to expand...

There's an opportunity for you. Go for it.
 
BRU said:
Just my 2 cents... If a ford distributor is Ventura vacumn only and a small block Chevy distributor vacuum advance is manifold vacuum, why can't you put a Chevy vacuum advance on an 8 ba distributor to make manifold vacuum usable? Better yet, why can't the internals of a Chevy distributor be made to fit inside the 8ba distributor for mechanical advance and eliminate the machining of the distributor, cutting of the shaft, making a hold down, etc., etc, to use on an 8ba and still have an all ford distributor?
Click to expand...

Assuming you are serious here, the Chevy vacuum advance unit does not work on it's own. The basic timing is controlled by the mechanical advance weight and springs, something the Ford loadomatic does not have. The Chevy vacuum unit just makes modifications to the mechanical advance. Without the mechanical advance unit don't think it would accomplish much. So you would basically have to attempt to get all of the Chevy guts into the loadomatic case. Not sure it could be done, but even if it could, it would take a LOT of effort.
 
BRU said:
Just my 2 cents... If a ford distributor is Ventura vacumn only and a small block Chevy distributor vacuum advance is manifold vacuum, why can't you put a Chevy vacuum advance on an 8 ba distributor to make manifold vacuum usable? Better yet, why can't the internals of a Chevy distributor be made to fit inside the 8ba distributor for mechanical advance and eliminate the machining of the distributor, cutting of the shaft, making a hold down, etc., etc, to use on an 8ba and still have an all ford distributor?
Click to expand...
The physical size of the GM distributor is bigger than the flathead distributor.
Perhaps if you could invent a 'component shrink-er' you could stuff the guts of the GM distributor inside the flathead distributor.
 
Thank you tubman. You are correct, that should be required reading lol. I am not sure if the spark control valve was genius or not. Must have been. Looks like chevy dist. is in my future. Will run stock for awhile. Main aim in beginning was to increase spark.
Have since learned thru research on this forum about battery drain, cable size etc.
What a good group of guys here on this forum, many thanks
 
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