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Originally Posted by ERTW
a point to consider is that operating a gasoline engine closer to peak torque rpm at certain loads improves bsfc. l question the mpg predictions. 111 mpg at 55 mph seems optimistic.
better aero, along with good door seals, eliminates wind noise. lrr tires make less noise. and a large enough muffler quiets the ice. the high number of ratios in new transmissions are actually meant to keep engine rpm low for low noise and vibration - not much to do with fuel economy. running at peak torque - for best efficiency - negates the extra gears. engine noise will dominate at 100 mph. unless you get a torquey diesel that operates at 1300 rpm.
the 112 bhp opel eco speedster got 113 mpg at 140 mph!
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For the 55 mph numbers I just used what Honda had published for their 'conventional' car,and taking the R-R power directly off the curve and calculating the aerodynamic road load HP for the new CdA,I got the new 55 mph road load.Then using the Honda's 0.448 lbs per brake horsepower-hour BSFC and a simplified 6-lbs/gallon,it spit out 111 mpg allowing for the Chrysler/Gino Sovran/Wolf Hucho gear-matching.
When the 3-Musketeers streamlined the DeSoto Airflow,they used a constant BSFC to dial in the gearing to maximize mpg.
The 1977 VW 'Safety' Rabbit @ Cd 0.125 would have seen 93+ mpg at 56 mph,up from 68 mpg.
I think that the Cd 0.195,1978 M-B C-111 III attained 17 mpg at 225 mph.
The 1982 VW ARVW got 39 mpg at 155 mph.
I would certainly like to verify the claims,but until then must rely on SAE prediction tools.
PS I ran the numbers for the 2013 VW XL1.With the 1996 Honda gasoline technology,the VW would see about 46 mpg at 100 mph.
If it were increased in frontal area from 1.5m-sq (16.14 sq-ft) to accommodate 4-5 passengers it would require more horsepower to sustain 100 mph.