My current research indicates the Allison 2500,2550 has the 3.51:1 ratio,
    the 2100,2200 series has the 3.10:1 ratio. Would anyone know what
    production
    vehicle uses the Allison 2500,2550 trans ?

    Thanks, Steve Carlisle

    I would guess just about all American made Tractor Trailers .
    It is very common. Is there an automatic transmission repair shop
    in your town? They would know.

    Paul Lamar


It came on the International Trucks but also in School buses,
Motorhomes and other specialty trucks here is pdf..I' m not sure if it helps!

Javier Perez


Newton Meters times .74 gives foot pounds. Converted.

The HP numbers are roughly based on 2000 RPM input.
With 6000 RPM input the HP numbers are three times
the numbers shown in this pdf.

For example the model 2500 HP is 300 so that translates to 900 HP at 6000 RPM input.
The torque input which  is the key factor is 895 NM times .74 gives 662 ft pounds.

That is like a two rotor running at 90 inches of Mercury (Hg) at 6000 RPM.

It would be way overkill even for the 650 HP TTC engine.

The torque converter probably limits the input speed to the torque converter
at 3800 RPM but we are not using the torque converter. These rough conversion
numbers above just deal with the roughly  the 3:1 planetary gear set.

Just like the Bell 47 gear box used in the TTC had about 250 stock HP in and about 350 foot
pounds of stock torque in the helicopter. According to the Bell engineers the box
was good for 1000 HP with 6000 RPM input.

If you are doing a highly turbo charged 3 or 4 rotor the Allison may be  a better choice.

Ford claims 650 foot pounds for a Power Stroke diesel pick up track
and that six pinion planetary is what is found in the auto gear box for that
truck. The more the planets the better. As I recall the P&W R-4360 had 18 planets.

So far the Bell is showing no problems in the TTC. The mag case drilled gears
Bell box is about 45 pounds.

Paul Lamar

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