I drive a Ford E-350 with a 7.3L Turbo diesel 7.3L poweratroke but it is just stock. 245HP... it is fun to drive though... especially when you are on the autoban barreling down the road at 100mph in a passenger van. It gets 18-20 mpg too... I was reading some forums and some guys claim to have a chip and turbo that boosts the engine up to 500 hp not sure about the torque though. that would really by tough on the transmission... it is sort of lazy and clunks into overdrive too soon. I would say it is a 1 mil. mile motor if you take care of it though.
Sadly ford downtuned the engines in the E series due to lack of air flow