Quote:
Originally Posted by Lonesome Trail
By your logic Car A is using less fuel because it's a small engine making more power per displacement, hence is more 'efficient' because of that ratio, correct?
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Maybe. Trouble is, you're using a very simplistic model of something that's quite complicated. The power produced by an engine isn't anywhere near as simple as a fixed ratio of X fuel in produces Y hp. It depends on all sorts of factors like valve timing and the speed with which the valves can open & close, internal friction, and much more. That's why each type of engine has its own BSFC map, which shows efficiency under various conditions.
The bottom line is that while it's possible for a larger engine to get better fuel economy than a smaller one under particular conditions, you pretty well have to deliberately seek out those conditions by e.g. looking at the BSFC maps for both, and choosing to run the larger engine at its best point, and the smaller one at its worst.