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Old 03-21-2008, 09:57 PM   #18 (permalink)
Randy
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Quote:
Originally Posted by Frank Lee View Post
randy: thanks for the explanation, I still am not fluent in what exactly mep means to efficiency.

Here's the graph I'm talking about.

I'm not really fluent either, but the graphs in the book RH77 linked to use that. I think Mean Effective Pressure relates to a pressure plot of the whole engine cycle, with the area inside of the curve being the effective pressure. This is easy to plot, and so has been used for describing engines since they started making them.

Quote:
Originally Posted by Frank Lee View Post
The root of my question started with knowing my car is geared for 1000-1200 ft/mn at 50-60 mph. Seems perfect right from the factory doesn't it? Yet our pet theories for increased fe mods almost always include taller gearing. WTH?
That is easier to answer. If the link above worked, you can see how little power you need vs. what's available. When you go to taller gears, the MEP goes up, pushing you up towards higher efficiency. If you could control engine size, you might go with higher piston speed, but if you can't lower should almost always be better.
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