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Old 07-12-2008, 04:26 PM   #27 (permalink)
aerohead
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piston speed

Quote:
Originally Posted by Frank Lee View Post
I don't recall where, but someone once provided a link to an engineering text that mentioned 1000-1200 ft/mn as optimal piston speed for economy.

My question is, is that true and why is it?

Why wouldn't, say, 700-840 ft/mn be even better?
Boy Frank,that's a new one for me.Although many things are new to me.I was looking at BSFC maps last night and don't recall a term like that even on the charts.Rpm seems to matter.Road load is an issue.Volumetric efficiency.The oil ring,by itself,is supposed to be responsible for 10% of all engine friction.And friction is given as a square function of rpm and is borne out by the curves for internal friction.I'll look into it,but off the top of my head,I'm clueless.It's worth knowing,and it seems like there would be a context to if making such a general claim like that.Maybe there's a powerplant expert in the house?
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