Quote:
Originally Posted by Merlyn2220
So I started hacking off some of the rear of the shell, in an attempt to figure out what was going on with the cavity and taper. I removed the center upper section (with taper) at about 100 miles into a tank, and ended up with 14.27mpg. With the 12 degree side taper and upper section and A/C use I was around 13.9-13.9mpg. So the center was a definite negative, even with a reasonable taper.
At 240 miles into the next tank, I hacked off the sides to be ~4" long, following the general shape of the body from a side view. 15.24mpg is a dramatic improvement over the previous tanks. HOWEVER....part of that is because I was having overheating problems and not running the A/C much, and driving slow to keep the highway temps down. This followed up with 15.67mpg for the next tank, with no other aero changes. I'd attribute the extra 0.5mpg to mostly driving well under 70mph on the highway while I swapped parts (thermostat, pump, hoses and radiator) and it seems to be back to normal. So this tank should tell me what real impact there is from hacking off my abomination of a tail!
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*Driving 70 mph vs 55 mph would effectively increase your drag by 1.619 X
*It 's like increasing the Cd by the same factor.
The 'naked van,@ Cd 0.38 would go to Cd 0.619.
*Aero power and fuel would increase by 2.061 X.