Quote:
Originally Posted by PeterS
I've been looking at a variety of bikes from the perspective of building an aero tourer and it seems that there is a significant advantage in fuel injection. The trouble is that here in Australia the only fuel injected bikes are quite big, usually 750 cc and up (especially at a price I can afford).
I could go to a smaller carbed bike but a question first about horsepower potential and used horse power.
With a cd of 1.0 a K75 BMW gets 43 mpg US at 70 mph as the spec sheets say. But using the calculator at the top of this page if I feed in a cd of .4 (as in a full Vetter fairing ) it says I will get 99 mpg US.
Is this believable?
Firstly this is a large engine , a 3 cylinder 750 but also a very good one that has an early fuel injection system. If the reduced drag only requires 8 hp versus 17.5 hp with a cd of 1( per the calculator ) is that all the engine will develop ? Meaning only using that much fuel .
Any input is welcome !
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General Motors published a relationship between drag reduction and mpg which is valid if BSFC can be maintained.
A 10% drag reduction will net a 6% mpg improvement at 70 mph.
Going from Cd 1.0,to Cd 0.4 is a 60% drag reduction and should produce a 36% mpg increase.
1.36 X 43 = 58.48 mpg if all other factors are held constant.
If the frontal area were to be reduced as well as the Cd,you could expect better numbers.
NOTE: it is essential to do gear-matching after the streamlining such as to maintain the same engine loading as existed before the streamlining or you risk losing up to 60% of the benefit.