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Originally Posted by CanAutM3
I am not sure I follow you here. For a total cycle (2 complete rotations), the area exposed to cylinder pressure should be the same regardless of cylinder count.
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That's true, but - and this gets into the complexity that I was talking about earlier - the summation of all the forces on the crankshaft at any particular instant will be limited by the maximum force applied during a single combustion event.
Even if we assume zero friction in the system (just for simplicity), the more cylinders the engine has, the smaller the maximum force available to act on the crankshaft. Consider a 100 or 1000 or 1000000 cylinder engine. One tiny piston applying force to the rotating mass at any given time. As cylinder count goes up toward infinity, there is not even enough force to turn the engine over. As it goes down toward 1, that force is maximized. It is true that more cylinders mean more chances for combustion. However, it is a bit like beating on a piece of sheet metal with a sledge hammer once every few seconds vs. tapping on it with your fingers very quickly. The former has a much more significant effect. Okay, well your fingers don't have as much mass as a sledge hammer - so lets use a rubber mallet instead, and maybe you are wearing some serious SuperBowl-ring-like bling on each of your fingers when you are doing the tapping. Still, you get further with the mallet.
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However, an engine with a larger cylinder count will have more friction losses. Just considering the piston/cylinder interface, the bigger pistons have a better area to circumference ratio.
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Yes, and that's a good point. However this is true only assuming a similar compression ratio since a higher compression engine will require a larger ring- to-cylinder contact area to avoid excessive blow-by.