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Old 01-11-2015, 08:16 PM   #15 (permalink)
some_other_dave
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You can also think of this as a 3D graph. The X and Y axes are, as stated, RPM and (effectively) torque. The Z axis, coming out of the screen, is fuel used per HP generated. The red is the lowest fuel per HP, yellow is next lowest, then green, and so on, up to the light-green which is the most fuel used per HP. The 3D shape is a bowl, with the highest edge of it at low load, and the bottom of the bowl being where the red zone is shown.



We'd love to stay in the high-load low-RPM regime, but that makes enough power to accelerate us. So we either have to stay in low-load low-RPM, or we get into the high-load low-RPM to accelerate, then coast. (That's "pulse and glide" or "pulse and coast", and can give very good results when done well.)

-soD
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