Dang, data for the 1981 VW Rabbit is hard to find. I at least got this much hard data:
Weight: 1755 lbs. (Est. with driver & fuel = 2000lbs)
Height: 55.5 in
Width: 63.4 in
Frontal Area (x 0.84) = 20.52 ft^2
So here was my input data for the calculator Metro linked to:
Weight: 2000lbs
Crr: 0.01
Cd: 0.35 (guesstimated)
A: 20.52 ft^2
Air Density = 1.22 kg/m^3
Then I repeated for a Cd estimate of 0.25 (achievable?)
I remember someone said they were going to get about 1800rpms at 61 mph. using this effective gear ratio, we can plot the estimated road load for the two aerodynamic drag coefficients. Because the online calculator spits out data every 5 mph, I used 60 mph for my own calculations of the HP, to torque (to BMEP) required for this speed given each Cd.
Now, interpolating BSFC values from the chart, we get the following (lets see iif I've figured out the table formatting yet...)
| . | mph | rpm | load(kW) | BSFC est. | gal/h | mpg |
| Cd = 0.35 | 60 | 1770.5 | 10.23 | 255 | 0.811 | 73.98 |
| Cd = 0.25 | 60 | 1770.5 | 7.99 | 279 | 0.693 | 86.60 |
So, there you have it. 74 mpg even without any aero mods (provided my various assumptions all somehow perfectly correct).
100mpg could be possible..... don't settle for 70!