[Dane-ger]

Actually...if you were to pull out 2 of the pistons and rods on a 4 cylinder engine in such a way that you kept an even firing order (such as 1/4 or 2/3) and removed the rocker arms on the dead cylinders so the valves stayed closed, that would cut your displacement in half (Should probably modify the counterweights on the crankshaft to keep it as balanced as possible). If you removed pistons 1/3 or 2/4, etc...you wouldn't have an even firing order but the crank would be better balanced as far as mass is concerned. This would probably require the best crank damper available either way. Then if you turbocharged it, used thermal barrier coatings and minimized engine drag and rotating mass...that would probably get you about the best fuel economy possible without making the thing too unbearable to drive.

Removing pistons like this is a pretty extreme way to modify an engine that I've never seen done, so I'm not sure the thing would run smooth...but it would cut the displacement in half which should help in theory.