Quote:
Originally Posted by RobertSmalls
A 0.5L, 55HP diesel delivers better MPG than a 1.5L, 160HP diesel because it tends to operate closer to its limits, where engines are more efficient. (This car will probably require ~20HP for highway cruising.) Because it and the electric motors are smaller, they have less internal friction, and they weigh less. They can also have smaller driveshafts, fuel pumps, etc. which save weight and money throughout the car. That, plus tires, spells out the difference between a high tech, high MPG car that I would buy, and a high tech, high performance car that I wouldn't.
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Are engines really more efficient at their limits, or does it just happen that engines are tuned in such a way that a small engine is more efficient than a big engine, aside from the reciprocating mass difference?
I think a 1.5L diesel could be almost as efficient if it's tuned and set up to take advantage of the hybrid electric motor assistance. For example, instead of spinning at 2000rpm on the highway, spinning at 1000rpm, since accelerating can be handled by the electrics.