[aerohead]

Hello all.Geebee had posted a thread which got cfg83,akashic,PaleMelanesian,some_other_dave,and myself off into BSFC,as related to drag.I was reluctant to get into it without my references,and I also thought this was of such general interest,that it deserved it's own "thread" in the aero "sticky".

First,let me apologize to anyone who went off on a wild goose chase in Hucho's book looking for the nuts and bolts on this topic.I found the material I was thinking of,and while Hucho touches on it,the following fleshes it out better than anything I've run across.

The reference is:SAE Paper#830304 "Tractive-Energy-Based Formulae for the Impact of Aerodynamics on Fuel Economy Over the EPA Driving Schedules",by Gino Sovran,General Motors Research Laboratories,presented,International Congress & Exposition,Detroit,Michigan,February 28-March 4,1983.


The paper revolves around changes in fuel economy" resulting from specific changes in one of the overall vehicle characteristics.",specifically,"resulting from a prescribed change in tractive energy"--- "The only direct change considered is -----resulting from a change in aerodynamic drag."---------------- "If the tractive energy is reduced,bsfc will usually increase because engine operation occurs at smaller fractions of full load.Since bsfc is the dominant multiplier in the fuel consumption equation the possibility that it might change must be accounted for."------------------------- "Fuel economy studies -----show an essentially linear relationship between g (fuel economy[my italics] and CdA for any given vehicle----."------------------"Without appropriate drivetrain changes to accomodate the reduction in CdA the impact of fuel consumption is only about 60% of what is available and attainable."------------------- "(engine speed / vehicle speed ratios desirable for low-drag vehicles may not always be available-------------------- particularly for vehicles with spark-ignition engines."

Too actually ascertain all the data to intelligently analyze and arrive at the "best-fit" gearing for highway mpg may prove daunting for the mere mortal.I furnish the information for those who intuit that they should be achieving better mpg because of their mods.There appears to be a bonafide scientific explanation for how that could be the case.

And the long answer to the question stands on the evidence,yes,aerodynamics directly impacts BSFC.