Forced induction compared to number of cylinders
 

1 cylinder fires every 720 degrees of rotation

12 cylinder fires every 60 degrees of rotation

http://www.epi-eng.com/piston_engine...on_engines.htm

the closer peak torque is to the average torque of an engine , the more efficiency gain possibility there is in a car..... Not talking about engine efficiency or volumetric efficiency , but just MPG efficiency...

The closer the peak is to the mean torque , whether your using a turbo or a supercharger because a turbo will have the same relationship but just with exhaust flow...

The more MPG increase window you have to take advantage of by saving weight going with a smaller motor and keeping the SAME POWER as you had with a larger motor....

from sitting down and thinking this is how my mind has worked it out as..... So the lighter motor you have , the less of a window you have for replacement improvement , the more cylinders you have the larger that window... Since larger motors are normally heavier , pretty much the relationship equals down to...

the more cylinders the more likely you are to have a mpg improvement from a smaller displacement forced induction motor. While the opposite is true with less cylinders.

Keeping in mind that volumetric efficiency is not MPG efficiency , which is what this whole post is about... and only about ... just MPG efficiency , not engine efficiency or VE