Hot Rods 59A vacuum port for crab type dizzy

So I've seen too types of vacuum ports being used on the flathead. One on the back side of the carb (mid section of the carb on driver side) and the other, right off the intake manifold where the wiper vacuum line is connected.
Which one should I use and why ?



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The one off of the back of carb is for 8BA engines with load a matic dizzy.....it advances timing.
On some crab tyoe engines there is a vac brake & i'm ignorant as to their function. Hope this helps.

 

Your 59A crab distributor's vacuum brake port should go to full manifold vacuum. The rear port on later '49-'53 Ford/Holley 94s should only be used with later loadomatic distributors.

 

Thanks guy! I'll tap off the vacuum for the wipers.


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The vacuum brake functions by the increase in vacuum from a reduced load pulling back a piston whose face rides against the dist. weights.
The piston being pulled back allows the weights to increase their rotational arc which advances the spark. An increase in rpm will also increase centrifugal force on the weights, also allowing the weights to widen their arc and advance the spark.
There is a spring behind the piston, and the spring compression can be adjusted by loosening the lock nut and extending or retracting the screw that pushes in on the spring.

 

The load-o-matic distributor used venturi vacuum to approximate engine speed and manifold vacuum to gauge engine load. That distributor had no mechanical advance. The venturi vacuum acted on one diaphragm to advance the timing with rpm.

 

Forge on fearlessly because if Plan A vac source isn't perfection, it should be reversible and easy enough to go to Plan B.