How To Get 99.7 Mpg From A Geo Metro

One year ago, Darin Cosgrove of Metrompg.com entered his Geo Metro in the Green Grand Prix fuel-economy competition. Over the course of the event, he coaxed his 12-year-old car to almost 100 mpg! Here's how he did it. —Ed.

How To Get 99.7 Mpg From A Geo Metro

Last May, alt-fuel and efficiency enthusiasts gathered in Watkins Glen, New York for the fifth annual Green Grand Prix expo and fuel economy rally. I entered my modified 1998 Pontiac Firefly (Geo Metro) in the rally and managed to score the top result of 99.7 mpg (US) (2.4 L/100 km / 119.7 mpg imperial) in a field of 25 vehicles — a field that included hybrids, diesels, and even a pair of Vespa scooters! How does one squeeze 99 mpg from an old Metro? Here's the recipe — mods and driving techniques — used for the event.

The Route

How To Get 99.7 Mpg From A Geo Metro

The competition covered a 79 mile/127-km circuit around Seneca Lake in New York's scenic Finger Lakes region. Drivers had two hours and five minutes to complete the course, consisting of both urban and rolling rural roads, where speed limits varied between 35 to 55 mph. According to organizers, the time limit was based on driving no less than ten percent below the posted speed limits; it also included a mandatory ten-minute rest stop in the city of Geneva.

The weather was ideal: sunny and mild and only light/variable winds. (So variable that I actually noticed tail winds in both directions!)

The Mods

Click on each link for a detailed description.

Aerodynamics:

Drivetrain:

Electrical:

  • plenty of use of the shifter-mounted ignition kill switch (for pulse & glide, engine off coasting)
  • alternator electrically switched off past the half-way mark
  • daytime running lights used selectively depending on perceived risks (installed an "off" switch)

Instrumentation:

  • ScanGauge, monitoring: instant MPG; tank MPG; average speed (time limit); open/closed loop; voltage (after switching off the alternator); elapsed time (watch)

How To Get 99.7 Mpg From A Geo Metro

The Driving Techniques

  • Pushing the car (part way) to the start; at the mandatory rest stop in Geneva; in the gas station for the post-competition fill
  • Pulse & glide on the highway portion of the route, monitoring the ScanGauge to keep engine in closed loop during pulses
  • Light timing & traffic timing in urban areas to avoid stops & minimize slowdowns ("driving without brakes")
  • Moving to the extreme right of my highway lane ("ridge riding") or part way onto the paved shoulder to facilitate/encourage passing by faster traffic (there wasn't a lot).
  • and more than a few other from our 100+ eco-driving / hypermiling tips.

The Dispute

There was some debate after the event about the accuracy of the fueling method — and therefore the accuracy of the fuel-consumption figures.

Prior to the start, drivers topped up their tanks at a gas station in Watkins Glen under the watchful eyes of rally scrutineers, who sealed all fuel caps with tape and a dab of silicone.

Competitors were instructed to stop filling at the first "click" off of the fuel pump. When the rally finished (at the same gas station, under the same scrutineers' watchful eyes), competitors again used the "first click" method to refill their tanks and thus measure fuel consumed.

Ideally, a driver would want to actually see the fuel level in the filler neck to ensure accuracy (particularly with such small fills). But filling to the brim can be a potential problem for vehicles with evaporative emissions systems, which draw vapour from the top of the filler neck. Filling to the top of the neck could cause liquid fuel to enter the evaporative system, potentially causing malfunction or even damage. Thus the decision by organizers to use the "first click" method.

Ironically, the more efficient the vehicle — the smaller the amount of fuel used — the larger the potential margin of error in the the "first click" method.

The important question: Was the 99.7-mpg result accurate? Short answer: because of the filling technique, it's impossible to say for sure. But it's definitely not outside the realm of possibility. I've regularly exceeded 100 mpg (US) for round trips under ideal conditions. And last summer I drove for a tank achieving 104 mpg (US). Considering all the stops were pulled out at the Green Grand Prix, 99.7 isn't that much of a stretch.

How To Get 99.7 Mpg From A Geo Metro

Other Class-Leading Competitors

Several other EcoModder members also competed in the Green Grand Prix, turning in some impressive numbers:

  • Ben Jones (SVOboy) returned 88.2 mpg (US) (2.7 L/100 km / 105.9 mpg imp.) in his modified Honda CRX with its lean burn engine & taller gearing
  • Will Meredith (Wonderboy) squeezed 57.2 mpg (US) (4.1 L/100 km / 68.7 mpg imp.) from his aero-modded 1998 Honda Civic EX coupe
  • Tim Sullivan (McTimson), using driving technique alone (and MPG instrumentation), got 53.1 / mpg (US) (4.4 L/100 km / 63.8 mpg imp.) from his unmodified 1993 Toyota Tercel.

Congrats, guys!

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