Quote:
Originally Posted by drmiller100
Which is more efficient - a 500 cc engine running at 4000 rpm or a 2 liter engine running at 1000 rpm)? If both vehicles have the same intake vacuum (measure of throttle and engine efficiency), then I would bet on the 2 liter.
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I agree. I think a lot of this has to do with stroke and RPM. If you look at any of the super-efficient industrial diesels out there, they run at extremely low RPM and have an insane stroke. They are getting absolutely every last ounce of expansion energy out of the gas before the exhaust stroke begins. Running a short stroke and/or high RPM will allow you to make more power, but at the expense of efficiency. The other downside of the low-RPM long-stroke engine is that its specific output (HP/LB) is extremely low.
Here's an article on the most powerful engine in the world... over 50% thermodynamic efficiency!
Most powerful diesel engine in the world