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Originally Posted by ProDigit
The larger combustion chamber actually is much more efficient than a smaller chamber, as MORE of the heat is converted to motion, not less.
The cylinder walls of a small engine drain more of that energy than on a bigger engine.
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Sorry but this is totally wrong. Larger combustion chamber areas will absorb more of the heat energy through their surface and waste it into the cooling system. And I believe that combustion chamber area is a bigger factor in heat absorption than swept area because peak temps are already dropping by the time the piston has moved down exposing the cylinder walls. So long stroke engines are more efficient than over square engines. And a single cylinder of the same bore/ stroke ratio and displacement has less surface area in the combustion chamber and is more efficient than a twin.
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Quote:
Originally Posted by ProDigit
A 650cc engine would need to run at 1500RPM to have similar MPG, but that would lug the engine.
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Now you are starting to get it. There is a big difference in efficiency throughout the operating range of an engine. Full throttle at somewhere just below the first torque peak can be nearly twice as efficient than a larger engine running at 20% throttle or running wide open at too low an rpm. Look at some BSFC maps and you will understand.
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This is why most vehicles have to Pulse-n-Glide in competition to get the best efficiency. They are way too powerful to keep a steady speed when operated in their efficiency band. The engines are way too large.
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Also keep in mind we are discussing the possibilities of ready to drive products. Not something theoretical that you wish to create in your lab.