The calculator is a good tool, but it is not a perfect tool. So I use it as a guide, but it cannot replace real world data gathered out on the road.
The calculator showed that my car, fully optimized with 0.15 Cd, ~30% engine efficiency, ultra LRR tires, weight reduction and geared correctly @ 45 mph should be capable of around 125 mpg. Can that be true? Maybe. Though I have the problem of having too big an engine, but that is going into deeper waters than is needed here.
I think you are correct, but in most cases turning higher rpm = more fuel use, regardless of efficiency. I still say you should do coast down testing and tell us what you find out about Cd & RRC.
Back on topic...
This 70 mpg kit would have to appear like this Dream Prius I found at either Gassavers or CleanMPG.
