[Power Hungry]

Originally Posted by cleatus12r

I'm not sure how much the Allison in it can take above and beyond the rated power as they're mechanically calibrated for a specific power output.

It's not really worth adding power to and I did 10K-mod it years ago....still a turd.

Torque capacity depends on the model of trans.

AT 545 - Good for up to 445 Ft. Lbs.
MT 643 - Good for up to 700 Ft. Lbs.
1000 Series - Good for up to 650 Ft. Lbs.
2000 Series - Good for up to 650 Ft. Lbs.
3000 Series - Good for up to 1250 Ft. Lbs. (in certain gears)

Most of the lighter duty applications use the MT 643 or the 1000/2000 series which clearly limits allowable torque output. However, since most of these engines have low HP output at the rated RPMs, the actual torque outputs are pretty low, too. For example, a T444e with a rated HP of 175 @ 2300 RPM produces about 400 Ft. Lbs. of torque. Bumping it up to 250 @2700 RPM moves the torque curve up to 480 Ft. Lbs. which, while being a bit high for an AT 545, would be well suited for an MT 643 or later model trans.

Of course, if you're running a manual then you shouldn't have any problems at all. The Eaton trans commonly found in them (the 5+1 and 6+1 O/D models) are rated north of 700 Ft. Lbs.

All this to say that unless the truck has an AT 545 in it, you should be able to safely bump the power up around 60-70 HP without any significant drawbacks or reliability issues.