246 MPG Vehicle

I recently had someone declare BS towards my claim of building a 246 MPG bike.

Honestly, I still remain a bit shocked about the measurement myself. Although since my original test rides (and related measurements) were over five years ago, and because I didn't meticulously document the tests with videos, photos, or even an attempt at accurate fuel input measurements (I trusted the gas station pump's measurement). What follows is solid mathematical proof of my claims, in human-approachable terms.

Baseline Numbers

  • Claim: vehicle gets 246 US Miles Per 1 US Gallon, as personally verified on two test/measurement rides that were about three months apart.
  • Engine: is a 24.5cc EHO25-R/S Robin-Subaru 4-cycle engine, with a factory-tuned centrifugal clutch.
  • Engine had about 100 miles of pre-existing usage, prior to the first test, and around 1,000 miles of usage by the time of the 2nd test.
  • Manufacturer Specifications (page 18):
    • Max Output: 0.81kW (1.1HP) @ 7,000 RPM
    • Fuel Consumption: 408 grams/kWh (300 g/HP*h)
  • Specific density of gasoline: 0.739
  • 1 US Gallon = 3,785 ml
  • 3,785 ml * 0.739 = 2,797 grams/gallon (gasoline density)
  • Average approximate speed was 20 MPH.
  • Gallon Gasoline Equivalent: 33.41 kWh

I rarely ran the engine at full throttle, as I had very conservatively adjusted the governor, to eliminate redlining risks. As a result, I estimate that I ran the engine at two-thirds full throttle; averaging 0.55kWh (550Wh) output.

Calculations

Analyzing fuel consumption over time & distance

  • .408 g/Wh * 550W = 224.4 grams/hour
  • 2,797 g/Gal / 224.4 g/h = 12.46 hours/Gal runtime
  • 12.46 hours * 20 MPH = 249.2 MPG

Heat Engine Efficiency

Just for kicks, we can also calculate the efficiency of this gasoline engine:

  • 2,797 g/Gal / 408 g/kWh = 6.856 kWh/Gal
  • 6.856 kWh/Gal / 33.41 kWh/Gal = 20.5% efficient