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Old 05-01-2012, 09:41 AM   #6 (permalink)
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80% load means the engine is producing 80% of the potential 100% which is maximum load in an engine in perfect operating condition. If atmospheric pressure is 30 inches of mercury, then the calculated 80% load would be 30X80% or 24 inches. A vacuum gauge would read 6 inches of manifold vacuum.
I think in reality it is closer to 2-3 inches depending on the engine and the RPM at which you are applying the load.
Take any engine, put it on a dyno and pick any RPM. Increase the load until you have 2-3 inches of manifold vacuum measured and you would be near 80% load, regardless of the RPM. 100% would be the maximum power that engine could produce and that specific RPM reading.
You also have to choose whether you are measuring horsepower or torque which would be at different RPM for the maximum the engine is capable of producing. Peak torque is efficient, while peak horsepower is not generally nearly as efficient.

regards
Mech
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