[ProDigit]

My response to single seater 100MPG at 60MPH:

I used to mod my Honda Rebel 250. It could get 110-120MPG at 45-60MPH.
That being said, forget about getting 100MPG out of any gasoline vehicle that's heavier than 500LBS.

I believe the optimal engine is a 300CC engine, single or ptwin engine, geared in such a way that it would reach 2k RPM at 60MPH in final gear.


Take reference car 2550LBS 'Fiesta ST' with 1 liter triple cylinder turbo enigne, and ~45MPG real life avg MPG.
Or, the Mitsubishi mirage with their 1 liter NA engine 2000LBS, 50 real life avg MPG car.

Then look at the highest MPG motorcycle (a 125cc Honda PCX) netting 115MPG. The next best one would be a modified Honda Rebel 250CC, which could net 105MPG.

If you plan on making a dual wheel vehicle with a 300cc engine and an aerodynamic shell, you could actually still get 100MPG, but that's about it.
For a 3 or 4 wheeled vehicle, you'll probably be limited to 75-85MPG at best, unless you run it on a track, and can do with an acceleration of 0.1 to 0.05G or so.

Even a modified Honda CBR300R for MPG, could only net 85MPG at best.
(and that was with modified ECU, and max gearing change possible, hitting 3k RPM at 60MPH). In theory it could hit 90-95MPG if it ran at 2,5k RPM.
This engine lugs at 2k RPM.

Edit: Like mentioned in the beginning of this thread, a diesel might get the MPG you'd want, and if you're ok with no acceleration, you could even hit 120MPG. The Kubota engines are probably going to be able to get the job done, however they're not a very pleasant engine for that purpose.
They are pretty low power, and don't have much reserve (meaning, you'll run a pretty low acceleration down low, all the way to up top of the rev range.