mitchell tansmission

K

kajnhedge

Member
can anyone tell me how much horsepower a mitchell modified model A transmission can handle? Also the over drive unit.
 
I assume you’re asking about torque and RPM. HP is calculated by combining those measurements, and you’ll get better information asking about them separately than by asking about a combined number.

Email mitchmanfc@frontiernet.net and ask the vendor directly.
 
alexiskai said:
I assume you’re asking about torque and RPM. HP is calculated by combining those measurements, and you’ll get better information asking about them separately than by asking about a combined number.

Email mitchmanfc@frontiernet.net and ask the vendor directly.
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Or better yet, call Steve Mitchell directly, 1.800.859.2088, you are much more likely to get a response than through email. But be prepared to have quite a chat, Steve and Cindi are two of the friendliest people you’ll run across in this or any other hobby. Leave a message if prompted, he will call you back.
 
Call Steve as mentioned above. But my engine puts out about 80 horsepower and the Mitchell transmission and overdrive handles that quite well. Alex, post #2, is quite right that torque and horsepower are two different things. My engine puts out maybe 30% more torque at the lower rpm but will only put out the horsepower at the higher rpm (3,000 or more) where the torque drops off.

I have not had this car on a brake to measure torque and horsepower so this is only a guess based on performance on the road.
 
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Here is a brake test (dyno test) of a modified engine: https://www.modelaparts.net/dynosheets.htm/dyno2.htm

If you click on that you can see that the torque is high at the lower rpm but falls off at the higher rpm. However, the horsepower increases with increasing rpm. The reason is because of the formula that Bob posted above. Even with the torque falling off the rpm is increasing so the horsepower is increasing.

The transmission must handle the torque without breaking. Horsepower is not a good metric to use when evaluating a transmission. A race engine is an extreme example. The torque can be low throughout the rpm range but because the engine turns at an extreme rpm the horsepower will be high.

All that said, high rpm may be detrimental to a transmission depending on if there are harmonic vibrations set up at the higher rpm.

More dyno tests at: https://www.modelaparts.net/dynosheets.htm/dynosheets.html
 
In racing
How fast you were going when you hit the wall is horsepower
How far you moved the wall is torque

These transmissions are very capable in 250 hp applications
You just have to be reasonable with the driving technique

J
 
johnneilson said:
In racing
How fast you were going when you hit the wall is horsepower
How far you moved the wall is torque

These transmissions are very capable in 250 hp applications
You just have to be reasonable with the driving technique

J
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Love it!!
 
Couldn't find actual specs but it'll take enough torque to get any 5 ton Model A moving.......

In 1990 after 12 years of successful overdrive sales in the full size vehicle market, it appeared that many small vehicles needed the additional gearing provided by our auxiliary transmissions. At the time, Glenn built the smaller auxiliary transmission Model 1000 at 10,000 #GVW to use in smaller vehicles versus the Model 3500 that was rated at 35,000 #GVW. After a couple of years of production, the Model 1000 had proven itself as a usable tool in the auto industry.
 
ModelA29 said:
Couldn't find actual specs but it'll take enough torque to get any 5 ton Model A moving.......

In 1990 after 12 years of successful overdrive sales in the full size vehicle market, it appeared that many small vehicles needed the additional gearing provided by our auxiliary transmissions. At the time, Glenn built the smaller auxiliary transmission Model 1000 at 10,000 #GVW to use in smaller vehicles versus the Model 3500 that was rated at 35,000 #GVW. After a couple of years of production, the Model 1000 had proven itself as a usable tool in the auto industry.
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Can you give me an example of a 5-ton Model A? :eek:
 
This is pure speculation, but maybe the present housing was a practical size for connecting the torque tube halves and gears to fill it resulted in the 10K# rating?

I had seen some reference to Mitchell making underdrives{?} for RVs, do they still do that or are they focused on Model A's? Also, I'm surprised that the OD's aren't adapted to flatheads, too.
 
I don’t have any figures to quote but I have no doubt that it could handle anything a banger could be built up to, no doubt at all. Also, long before the OD failed the tires would smoke. Now if you wanted to put in a V8 and fat tires and dump the clutch, it might break but even then I expect the trans would go first.
 
The key to putting more torque and horsepower through a transmission is to not shock loaded like dumping a clutch if you gradually apply the load you could probably put 350 or more horsepower through 1 of these transmissions all be it by not shock loading it!!!
 
nkaminar said:
Here is a brake test (dyno test) of a modified engine: https://www.modelaparts.net/dynosheets.htm/dyno2.htm

If you click on that you can see that the torque is high at the lower rpm but falls off at the higher rpm. However, the horsepower increases with increasing rpm. The reason is because of the formula that Bob posted above. Even with the torque falling off the rpm is increasing so the horsepower is increasing.

The transmission must handle the torque without breaking. Horsepower is not a good metric to use when evaluating a transmission. A race engine is an extreme example. The torque can be low throughout the rpm range but because the engine turns at an extreme rpm the horsepower will be high.

All that said, high rpm may be detrimental to a transmission depending on if there are harmonic vibrations set up at the higher rpm.

More dyno tests at: https://www.modelaparts.net/dynosheets.htm/dynosheets.html
Click to expand...

So what is corrected HP?

A stock A running at 55MPh down the road turns about how many RPM? A B carb, and Brumfield head reduces the RPM a measurable amount?
 
Don’t forget the rear end ratio as well. Most common for cars 3.78 and originally trucks were 4.11 (there are exceptions to most everything) I have yet to encounter a truck that still has the 4.11’s in it but I’m sure that there are a lot of them out there. I personally have no sat down with a calculator to sort out the details but I have been told that with an OD the 4.11 rear works well.
 
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