[QUOTE=MetroMPG;14524]Remember - a BSFC chart shows fuel consumption of a significantly LOADED engine.[/IMG]
I'm gonna have to disagree there. The Y axis on a BSFC map shows the load, in torque or engine pressure, from 0 to max for each rpm on the X axis. Though the max torque is at WOT, those low-torque consumption values must be measured at lower loads to create the entire map.
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I've just spent a geeky afternoon looking at every BSFC map I can find online. After isolating the maps for gasoline engines, I've got a few observations:
A - The peak efficiency islands, measured at the top, bottom, left and right extremes vary from 50 to 90% of peak torque for that rpm. The center point of the islands ranges from 62 to 79% of peak torque for that rpm, with an average of 72%.
B - Though peak efficiency islands' load is within a narrow band, their rpm width varies greatly between engines.
C - BSFC goes way up at low loads.
D - In general, the BSFC goes up after reaching peak torque.
My general conclusions and questions:
A - Can we infer % of max torque from TPS or LOD? (I would hope LOD is just that)
B - No conclusion, actually. Some engines may stay in their peak island with three gears, some may need more.
C - Besides higher BSFC during acceleration, it takes longer to get into top gears
D - I had assumed shifting to keep rpm's averaged at peak torque was optimum. I now think shifting *at* peak torque will result better FE.