I puzzled over what you wrote below, and then realized you meant 1/2 lb per hp-hour, not 1/2 gallon per hp-hour.
Many years ago, your figure (1/2 lb/hp-hour) would have been correct. Simple, carbureted engines are still in this range, at peak efficiency. (Of course actual, installed running efficiency is much lower, all the way down to virtually 0% when idling.)
Having designed, built, and used dynamometers, I'd amend your statement to read "Dynomometer
operators are infamous for producing bogus numbers." To make any useful sense, BSFC numbers are at the crankshaft, and crankshaft dynos can be reliable and highly-repeatable.
Too many people consider best fuel burn figures to be representative of average fuel burn figures when doing back-of-the-envelope calculations. It is a very rare engine installation that comes remotely close to best fuel burn at 55 mph. Where engines like that in the Prius and original Insight shine is in their ability to produce really good numbers at low hp.
Quote:
Originally Posted by owly
7 horsepower to go 55 mph.
typical internal combustion engine numbers 1/2 gallon per hour per HONEST horsepower...
Horsepower ranges mostly below the 1 HP per .5 gallon range, and very slightly above it........ There is a lot of lying done about horsepower and about fuel consumption per horsepower. If it varies much from that number for an internal combustion gas engine, someone's not telling the truth. Dynomometers are infamous for producing bogus numbers.
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