Hot VWs - December 2008 - Project Mileage Motor - Part 15
Testing different speeds, with wide ranging results
Mileage Motor: Part 15
BY BRUCE SIMURDA
This month, we're going to try something a little different with out Project Mileage Motor 1972 Super Beetle. Up until now, all of our mileage tests have been done on the freeway, at 65mph using the same route. For this month's test, we're not going to make any changes to our 1745cc engine (which received a single throttle body injection system last month), rather, we're going to change our testing speed to see how it affects our mileage.
If you remember, last month we installed a single two-barrel throttle body on our CB Performance Quick Tune EFI system, and resulted in a best EFI reading of 36.75 miles-per-gallon. (It should be noted that our absolute best mileage to date came in the October 2007 issue when we ran dual Weber ICT carbs with the Doug Berg Jet-A-Vator device installed between the carb and manifold, which resulted in an impressive 38.36 mpg.) So for our tests this month we're leaving the engine untouched, and beginning by running the same course at 75 miles-per-hour. Of course, we were expecting a drop in mileage by this 10 mph increase in speed, and we weren't disappointed, as our fuel consumption dropped considerably to only 30.95 mpg. That's a drop of 5.8 mpg, or nearly 16%! Guess the not-so-stealth aerodynamics of the Beetle really come into play here!
For the next test, we slowed down 20 miles-per-hour, to the California truck and trailer towing speed limit of 55 mph. Right of the bat I want to say that, on the freeways of Southern California, it certainly is easier to go 75 mph than it is 55 mph! Let's face it, at 6:00 in the morning people are in a hurry to get to work, and don't want to be delayed by a slow-poking Beetle. But we took the heat, and simply stayed in the slow lane as everyone buzzed past on their way to work in the morning. Add in the end, the results proved the slow and steady idiom, as we netted our best mileage yet, and nearly reached our goal of 40 miles-per-gallon, with a 39.1645 miles-per-gallon reading. That's a full 2.41 mpg, or 6.6% increase in mileage just by slowing down 10 mph. Compared to our 30.95 mpg reading at 75 mph, our mileage jumped 8.21 mpg, or 26.5%, by slowing down 20 miles-per-hour.
One of the premises of this series from the very beginning has been trying to obtain the best mileage possible in real world driving conditions, and we'd have to say that 55 miles-per-hour really in real-world driving. Although it's only an improvement of 2.41 mpg, it's something to remember the next time you're on a long drive to a car show - and you're paying $4 per gallon! Just like with any car, the faster you drive, the more fuel per mile you are going to consume, and this month's testing proved that. It's all very interesting stuff, and next month we'll once again try something new.