Vacuum advance spec

It is going to depend on several things including the engine RPM at the time you are taking the measurement. The 8ba distributor operates on vacuum only, so the vacuum will be low at idle and increase with engine RPM to advance the distributor.

Per the F1 Shop manual:

49 to early 50 in inches of mercury
200 rpm 0.0
500 rpm 0.4
1000 rpm 1.7
1500 rpm 2.8
2000 rpm 3.7

late 50 to 51
200 rpm 0.0
500 rpm 0.3
1000 rpm 1.32
1500 rpm 2.85
2000 rpm 3.7

I have no idea on the 53 Merc, but it should be in the same ballpark.

Note: 40 Deluxe posted a good explanation below. The vacuum numbers listed above relate to testing a distributor, not operational conditions.
 
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It depends on the amount of throttle opening combined with engine RPM. These two things determine what the load on the engine is at any given moment, which in turn determines the amount of ignition timing needed at that moment. This vacuum signal 'pulls' against the springs on the points plate to provide the correct timing for the load on the engine. Thus the term "Load-O-Matic". This system blends venturii vacuum with ported vacuum to give the correct signal so the OEM carb must be used. Early '50's Motor Manuals give a detailed explanation with diagrams to show how it all works.
 
According to my old Holley carb and distributor manual the specs for the '52 and '53 Mercury 255 teapot carb are exactly the same as the '49 to early '50 Ford specs posted by JSeery above.


As noted before, this is distributor RPM (half of engine RPM)>


Sal
 
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