Quote:
Originally Posted by Cd
Has anyone here tried this method ?
Anyone ?
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You mean besides me? I think a couple other people have in the past, but overall no.
Quote:
Originally Posted by redpoint5
No, it was not explained at all, ever. A change in BSFC at a given throttle position necessarily results in a difference in power output, and therefore speed. Just because fuel consumption is not being measured doesn't mean a change in BSFC is irrelevant.
Someone insisting something incorrect has still failed to answer the question.
Power is torque * RPM / 5252. A change in engine RPM at a given torque necessarily means the power output is changing.
Horsepower determines speed, not torque. Since a changing RPM affects how efficiently fuel is burned, and therefore power output at any particular torque, it must affect speed non-linearly.
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Power changes with a change in drag when torque is held constant by a constant throttle opening because power = (force)(speed). The change in drag shows up as a change in speed because the tractive force at the wheels is the same. Still has nothing to do with BSFC for this test technique because it doesn't matter how much fuel the engine is consuming in any configuration, only that the throttle opening (and torque output) is held constant.
When I had questions about this, I reached out to a UIUC engineering alum who works for an auto manufacturer. He wrote back, "Assuming a flat torque band in this speed/rpm range, your torque in both scenarios is the same, the speed of the higher drag car is slightly less, and as a result the power of the higher-drag car is slightly less."