[Diy_efi] Is E85 worth it? Speed factor?

[Robert W Hughes]

> Up to a point - I mean, you certainly don't get the best gas mileage at 
> 0 MPH!  There is some speed where a vehicle (probably different for 
> every vehicle) gets the best gas mileage.  I would at least expect it to 
> be in the top gear, and probably at a speed where the throttle is open 
> enough to minimize pumping loss, and at the same time maintain closed 
> loop operation.
> Somehow I doubt it's 55MPH - probably significantly faster for most 
> modern cars.  The whole idea of reducing the speed limit to increase 
> fuel economy is bogus.

Internal combustion engines do not have the same type of torque curve as 
a rubber band so the simplistic slow down and save does not work. When 
the 55mph limit first went into effect in 1974 I was driving a 1965 
Corvair Corsa with 4 carburetors and some modifications. At 70 I had 
been averaging 27mpg, at 55 I averaged 25mpg. As a slightly later 
example my 1987 Fiero V6 normally got 27mpg at 55. One day I made a trip 
at an average of 80mph and got 31mpg. I suspect that for a given body 
and engine size, gearing and breathing characteristics (camshaft) 
determine the road speed for best gas mileage and it is not always the 
speed desired by the anti-destination league.
-- 
Robert W. Hughes (Bob)
BackYard Engineering
29:40.237N, 95:28.726W or perhaps 30:55.265N, 95:20.590W
Houston, Texas "The city with too much Oxygen"
rwhughe at oplink.net