I've seen HUGE Fairbanks-Morse opposed piston engines driving water pumps at the Charles River Dam in Boston. These engines have a simply outstanding 40% thermodynamic efficiency (base on the LHV of fuel) when turbocharged.
The most interesting two stroke diesel I saw (well, as an article with photos in a magazine) was a compression ignition assisted Pogo stick! It was in the early to mid 70's and I believe it was Popular Science.
<edit> Well, it wasn't diesel after all. http://www.bpmlegal.com/wpogo.html <end edit>
If you want to see a massive diesel though, google worlds most powerful diesel or something like that. They're BIG guys used in commercial tanker ships. Turn at 100rpm making ungodly horsepower and torque and have something like 50% thermal effeciency in cruise mode.
simaler to how city busses only get about 4mpg...
compare work done, to fuel used, a contaner ship is hauling alot of stuff, each contaner is limited to what? 45,000 pounds? I think that's about right, and the ship has hundereds of contaners.