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Old 11-15-2011, 08:49 AM   #57 (permalink)
Frank Lee
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Join Date: Jan 2008
Location: up north
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Blue - '93 Ford Tempo
Last 3: 27.29 mpg (US)

F150 - '94 Ford F150 XLT 4x4
90 day: 18.5 mpg (US)

Sport Coupe - '92 Ford Tempo GL
Last 3: 69.62 mpg (US)

ShWing! - '82 honda gold wing Interstate
90 day: 33.65 mpg (US)

Moon Unit - '98 Mercury Sable LX Wagon
90 day: 21.24 mpg (US)
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VE is nice and all, but I was after the bsfc peak... the reason for an optimal piston speed has been mentioned earlier in the thread (thanks guys ) but I resurrected it just cuz I found this:

Sfc measures how efficiently an engine is converting fuel into work. The graph of an engine's sfc plotted against engine RPM will be "U" shaped. At high speeds the sfc increases due to increased friction, while at lower speeds the sfc also increases due to higher heat losses from the combusted gas to the cylinder and piston wall because of the increased time the hot gases remain in the cylinder. This is also the reason why air cooled engines are usually less fuel efficient than water cooled engines.
And also why there are differences in optimal piston speed between 2 and 4 strokers, and gas and diesel.

It seems in the case of my slow-turning F150 that too much of my gasoline's heat energy is going into the coolant. This also offers a partial explanation for why my fe DROPPED when I "geared" it down with taller tires- the other part being the effects of the tires themselves on aero and whatnot- but it tells me that were I to keep the original sized tires and gear higher with gears, chances are that would fail to improve fe as well.

Last edited by Frank Lee; 11-15-2011 at 08:54 AM..
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