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Ken:
Having been involved in experimental aviation for many years, I've heard countless wild claims on horsepower....... claims that are NOT borne out in real world performance. And with those exaggerated claims come proportionally exaggerated efficiency claims. I have seen nothing to convince me that real world efficiency is exceeded 1/2 pound per HP hour to any significant extent. There is a standard automotive engineering formula for horsepower versus CFM (actual), which also holds true in real life. That is 1.62 actual CFM of airflow required per brake horsepower. Intake efficiency runs from about 80% to about 80% typically, depending on RPM. I reached almost the identical number doing math based on manufacturer horsepower and torque ratings (deriving HP from torque & RPM using the formula T*R / 5252 = horsepower)........ Needless to say there is a "truth factor" involved here also. Now that they use net HP, it would be difficult to do.
I consider dyno operators to be liars for the most part........using their machines to produce falsely optimistic results for sales purposes..............
H.W.
[QUOTE=Ken Fry;389564]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.
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