Quote:
Originally Posted by wmjinman
4) That brings us to the surprise that it was so "straight"... I was expecting it to curve over sharply and to drop like a rock at 70 and above, but it didn't - just kept decreasing at about the same rate....
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That sometimes happens. Even though the aerodynamic load is going up dramatically as speed increases, depending on gearing and the engine in question, the engine may be be getting closer to its peak high-load efficiency zone - see
Brake Specific Fuel Consumption (BSFC) Maps - EcoModder
Approaching peak BSFC as speed climbs would tend to "flatten out" the line on the chart. (Moreso than you would see with an electric vehicle, by comparison.)