OD power

Pandersen33

Pandersen33

Member
I have fresh rebuilt 29 engine, snyder head, weber carb, Fs ignition... when i shift into 3 high with my Mitchell (55mph?) it doesnt quite seem to be able to accelerate too well. Is this the experience most have or should it be able to pull a bit more? Tach says ~2500 rpm and 62 mph. Timing set right around 28 at full advance.
 
Based on 2500rpm, 62mph and 26% Mitchell would guess it has a 4:11 ratio differential. If so you are about on the top of it.
 
55-60 MPH is plenty fast for a basically stock Model A.


I would keep the revs down around 2000RPM when at cursing speed.


At 2500, you are working the engine a bit too hard.


Again, this is just my opinion and I am sure others may have something different to offer.


Chris W.
 
As others said it sounds like you must have 4.11 rear axle ratio, and at that speed you are already well past the power peak. I also have a Mitchell 26% OD, and I usually shift into 3rd OD at about 45 mph, and on somewhat level ground, it does accelerate decently up to 65 or so. I have the standard 3.78 rear end and also the Snyder 5.5 head. Even with the OD I prefer to cruise at 60 mph most of the time.
 
It has been my understanding that the Model A was designed to run all day long at 45 mph with the engine turning over at a nominal 2000 rpm. With an overdrive you can increase the speed of the car and still maintain the engine turning over at 2000 rpm.

My Victoria has a 378:1 ring & pinion and a 23% Ryan overdrive. A while back I installed a tachometer and wrote an article about it. The article includes some speed\tac observations.

Tom Endy
 

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