From what Ive read from real world experience the best mpg comes from using a 3 cylinder geo or honda engine for gas powered and for diesel the 2 or 3 cylinder generator motors.
I use to read a geo form and it seems no matter how many mods you did it was nearly impossible to get the 4 cylinder version of the engine over 50 mpg, where with the 3 cylinder engine it took little to no mods.
