If you go to the part of the movie where Tommy Boy is talking to Mr. Zylinski and when David Spade's "wig" gets blown backward by the engine that is suspended by chains. You see the engine start, and the fan blows the fake hairdo backwards. Well, it seems relevant until you consider the fact that an engine's fan blows air backwards over the motor to cool it down. Another thing is that the engine never would've been able to run without a gas tank, starter, radiator, and other things required to run a normal engine.