[chisophugis]

FWIW, a single Boeing 747 engine does about 100MW. Such an engine can be considered to "fit on a truck" for some definition of truck.

Also consider that much of the size is due to the fan on the front (which is not part of the actual engine power plant), which makes the engine's area in the plane transverse to the axis of rotation seem larger.

However, jet engines have the advantage of burning their fuel directly in the air that is flowing through the engine, which results in an extremely rapid transfer of heat to the air compared to other (this is why 10 Boeing 747 engines == 1 GW coal/nuclear plant which is "buildings" in size).

See slide 25 (page 13) of http://ronney.usc.edu/AME436S13/Lecture1files/AME436-S13-lec...