Quote:
Originally Posted by mechman600
I don't agree. The Prius has a smaller engine than most that works WAY harder than most, which makes the car efficient. The idea is that if you use a smaller engine that is working at its peak (moving the car, charging batteries, or whatever), it will be more efficient than a larger engine not working at its peak. An engine is most efficient at WOT at peak torque RPM, in terms of energy produced compared to fuel burned. Unfortunately, at WOT peak torque, any car currently produced will be accelerating vigorously producing way too much energy.
I just came back from a road trip where I drove the steepest, hilliest highway known to man, the Coquihalla (BC, Canada). Lots of time is spent going up 8-9% grades (to 2 summits) and coasting down the backside. Fuel economy always ends up being the best in this situation because the engine is working at peak torque uphill, and coasting down (using zero fuel). My normal 44 mpg (imp) went to over 50 mpg during this segment. Anyway, that's off topic. Back to my questions please.
James
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The Prius has a variant of the engine in found in the Yaris/Echo/xA/xB1. However, instead of 105-108hp, it makes 76hp (IIRC). This is achieved through a valve cycle scheme that maximizes efficiency at the expense of power. As such, what mechman600 wants to achieve isn't completely insane. 50hp in a non-80s Civic would probably verge on undriveable, but changing the cams to keep the peak power at a low RPM would probably help a lot.
The Prius uses the Atkinson cycle, as opposed to the normal Otto cycle.
Atkinson cycle - Wikipedia, the free encyclopedia
In effect, it lowers the compression ratio by keeping the intake valve open longer than an Otto cycle engine.