the cummins 4bt is becomming more and more common in the fullsize rigs, expecially ford and gm because the 4bt comes with either a ford manual tranny bellhousing or a gm automatic bellhousing attached to it. mods for the cummins 6bt (12 valve) work on the 4bt with the exception of needing enough for only 4 cylinders instead of 6. better fuel economy as well. the best that i know of (confirmed) in a lifted 4x4 is 28 mpg at 70 mph (US gallons, not imperial). nv4500 5 speed manual tranny, 4.10 axle gears with 36x12.5" tires, 4" lift on an 80's era chevy blazer. cranking out around 500 ft/lbs of torque when he did the fuel economy testing. last time i checked he was over 900 ft/lbs of torque with that motor (he's trying to find out how much it can take), he's done alot of work to the motor.
