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Old 05-07-2019, 12:43 PM   #35 (permalink)
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Originally Posted by hat_man View Post
Someone suggested an indicator showing different colors representing the BSFC "islands" as a visual reference to help keep the driver in a better FE range (speed/rpm). Would an old school vacuum gauge do the same thing? Or is my confusion showing again?
I'm not so sure such a visual would help. A driver needs to travel a particular speed, and the only variable to maintain that speed is which gear they are in. Generally, you want to be in the tallest gear that will allow you to maintain speed.

Engines produce a certain amount of power at a certain torque and RPM. In fact, horsepower is torque * RPM / 5252

The reason that the BSFC map isn't that useful is that it doesn't factor in the other variables such as increasing wind resistance due to traveling faster. It simply shows the most efficient RPM and throttle position (torque) to produce a given amount of power.

MPG or liters per 100 km is a better measure of efficiency because it factors in all of the variables.

So, BSFC is a good tool for engineers, but MPG is the right tool for drivers.
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