VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 Looking for distributor with vacuum advance

I have a 1928 4 cylinder Roadster. I want to put a vacuum advance into the distributor. Is there anyone that does that? Or are the parts available for me to purchase and install? Any help and info would be greatly appreciated.

The 28 4cylinder is not engineered for that type of set up. The advance is set by the knob on the wheel for retarding for starting purposes then warming up the engine. Once warm the full mechanical would be 25 degrees, when over 18mph the distributor is all in at 50 degrees "ish". Adding a vacuum advance will give a little extra advance but you would have to limit the designed centrifugal which would net the same advance. Also if you are using a vacuum fuel pump, do you want to rob the fuel delivery while trying to advance the timing which would lead to a lean running condition, which give hotter cylinder temps which can create more problems with performance and or engine wear.

Proper timing valve adjustment clean points cap and rotor, and some good plugs you are pushing the limit for max hp. Remember max HP is 35, tons of torque but no real gogo.

I hope this explanation helps you in your quest. I am curious of the vacuum advance plan. What are you trying to accomplish? You may be onto something.

Thank you

Hi Richard

There is really no reason why you can't do as you have proposed.
And there is no reason why you shouldn't.
It WOULD however take a fair bit of work and experimentation.

EVERY engine will benefit from regulating the spark advance in response to the load on the engine
Up to about 1933, Chevrolet relied on the driver to accomplish this via the spark button or lever.
After 1934 a vacuum advance was added to what was essentially exactly the same engine.
The vacuum advance was really just a matter of convenience and adding a mechanism that did a better job than many drivers did.

You don't need to look for a distributor with a vacuum advance IN it.
The vacuum advance on engines up to and including all 235's was part of the mechanism mounted at the base of the distributor that rotated the WHOLE distributor, as well as holding it in the block.
That is where you could possibly adapt a vacuum advance to your engine while using the distributor you have.

The HARD part, would be the vacuum supply.
If you want the system to apply increasing advance with increasing engine speed as the 6 cylinder engines did, a port of just the right size would need to be drilled into the carburetor at just the right place near the throttle plate and a fitting adapted to it somehow.
That may NOT be doable
If you want the system to just perform the same thing your lever is doing, a simple tee into the vacuum supply to the fuel pump would suffice.
A vacuum advance really shouldn't affect your fuel pump at all as the displacement of the diaphragm unit on a vacuum advance is minuscule.
And vacuum isn't lost at this point, it is held.

If you could find or modify an advance unit to apply the same amount of advance movement as the lever does now,
and you set your initial advance to the same place it is now when your lever is in the retarded position,
it would work just fine.

I'm just not convinced it would be worth the trouble! 🙂

. Let me add a little bit to this subject. To achieve automatic spark, you need a centrifugal advance, Vacuum advance and "Knock detector". If you dissect your 34 Chevy distributor, you'll find the spinning weights that cause centrifugal advance when the engine revs up. If you see the vacuum advance and inspect the carburetor you'll notice it draws vacuum at the throttle plate. This retards when you first stomp on it before the centrifugal advances it but doesn't hold it retarded when the butterfly is open.
. You're going to have to wait till electronic ignition for the computer to listen for knock. Now. the fuel injector doesn't spray fuel till the appropriate time which is why diesels no longer "rattle" at idle.
. So if you're thinking about borrowing the distributor from an Iron Duke, Grab the carb and an electric fuel pump while you're at it. Or go to electronic ignition. (I wonder how many judging points you'll lose?)[I don't know the font for sarcastic.] .
. I had a Rochester carb on my 27 truck when I couldn't get the orig rebuilt. This was early 1960s before VCCA.
I sucked piston #4 after a few months of driving. What could I expect from something I drug out of the Russian River. .

Huh?

For what year and moter I got a good one for a 47 216 all new parts in it