I have an '90 Audi 200 Quattro wagon with about 260K miles on the
clock. In the last several years I've logged four 6000 mile trips to
the National parks. It's chipped for 15psi boost, with a larger
intercooler to give about 250hp, so it goes okay for a 21 year old
car. I run the GPS during the trips, and the moving average speed for
the trips has been fairly consistent at around 72 to 74 mph. To
average 72-74 overall, I needed to run ~ 85 mph on the interstate
highways, to average out the much lower speeds on secondary roads
etc. On these trips my overall mpg has varied from 27-29mpg, with
fuel stops about every 450 miles. This is total trip miles divided by
total gallons of consumed with two people and a lot of luggage as well
as a lot of miles in the mountains and on dirt roads. The GPS miles
run 5% less than the odometer miles, which is due to the tire size
being slightly larger than OEM.
I've mentioned the numbers to a few people, but most say impossible.
I remember reading literature that Audi put out when the Quattro's
were first introduced in the '80's that said in testing at speeds over
~70mph the overall rolling resistance of the tires is less when the
driving torque is evenly split among 4 tires vs 2 tires even when
losses of an extra axle etc are factored in. I think the other factor
is that the car is turbocharged which probably makes it a little more
thermally efficient, at least at higher speeds, and it's fairly
aerodynamic. In daily driving around town the mileage is lower,
around 18-20mpg which is not great compared to newer cars weighing in
the 3700 lbs range. Be really interesting to see if there are lower
overall losses at medium speeds with an efficient 4 wheel drive
system. The older Quattros had 3 differentials, an open diff with a
vacuam lockup in the rear, a Torsen in the center, and an open front
diff.