Dual advance distributor

[Les Schubert]

Finally have it clamped on!
A copy of a design of mine from the’80’s.

Borg Warner automatic for my wife’s speedster!

[Kaiser]

Now that's a first for me, an automatic behind a T engine, nifty setup !

[Les Schubert]

I’ve probably seen half a dozen of them over the years!

[TXGOAT2]

Some vacuum advance units connect to manifold vacuum, but many connect to a special vacuum advance port on the carburetor which is near the throttle plate.

[Les Schubert]

I will be connecting it to the intake manifold.

[Tom Dove Jr]

You’ve built this before? How much total advance did/will you run?

Tom
=====

[Les Schubert]

I haven’t researched that yet. Running a Prus head

[Erik Barrett]

Vacuum advance units are almost always hooked to ported vacuum. This gives them advance from just off idle to part throttle and takes it back when the engine is working hard at wide open throttle.

[AndyClary]

Vacuum advance is primarily a fuel economy feature. It allows more advance in the light throttle/low load than the engine would tolerate under load. The increased advance improves fuel economy. I’d be interested in hearing how this translates in a T. The centrifugal advance would have to come in pretty early.

Andy

[TXGOAT2]

I've had poor results with a street driven engine with centrifugal-only spark control.

The same engine/manifold/carburetor with a vacuum/centrifugal distributor with the advance unit connected to ported vacuum made a huge difference in overall performance and in throttle response.

[Les Schubert]

My previous one of the identical design has worked well for 40 years. The car is capable of 100 mph and is easy to drive (no spark management required). The 71 car it came from had it connected to the intake manifold.

[BobD]

Nice work Les. What did you source the distributor from? Some of the Model A guys have retrofitted a '70's Honda centrifugal / vacuum advance distributor with excellent results. However, the supply of these distributors seems to be drying up.