Hypermiler Squeezes Astonishing 40 MPG From Lightly Modified 1999 Chevrolet Corvette

It even has more horsepower than stock thanks to a custom dyno tune.

By James GilboyDecember 9, 2019

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Mile-per-gallon figures that start with four and consist of more than a single digit have long been the territory of hybrids, diesels, and other such vehicles that make most Americans hiss like your neighborhood's mean cat. That doesn't mean Keeping Up With the Hybrids is a show hosted exclusively by the Toyota Prius and Honda Insight, however, as its roster now features a surprising new member: The Chevrolet Corvette.

The Corvette earns its place among these mileage maximizers thanks to an experiment run by Chicago-based YouTube user LegitStreetCars, who decided he'd try to crack 40 mpg in his 1999 Corvette C5 without sacrificing any daily usability. To accomplish this, he gave his "Ecovette" the works, doing everything from a basic tune-up to pumping up tire pressures to 38 psi and replacing the engine, transmission, and differential oil. All of these were necessary to get the most out of the keystone modification, a custom dyno tune, which yielded not only a free 16 horsepower and 11 pound-feet of torque but also increased air-fuel ratios (AFR) toward the bottom of the rev range, where the C5 cruises at highway speeds.

Most cars run ratios well below gasoline's stoichiometric—or chemically even—ratio of 14.7:1, but LegitStreetCars's Corvette was tuned to run an AFR as lean as 17:1 with light throttle at low rpm. This meant that fuel use in that rev range was reduced by roughly one third versus the stock tune and, in ideal conditions, could result in mpg gains as large as 50 percent.


LegitStreetCars tested their modifications on a 314.6-mile drive from Chicago to Madison, Wisconsin and back, wherein the 'Vette used just 7.813 gallons of gasoline. That's an average of more than 40.2 mpg, or double what he was getting from the car in combined city-highway driving before the modifications. All this comes despite being caught in traffic, switching to neutral on off-ramps (leave it in gear, lad), and a suspected aftermarket thermostat that may have eaten some mpg gains. With a factory thermostat, taped-off body panels, more aerodynamic wheels, and better road conditions, who knows what's possible? Forty-five mpg seems attainable—we'll buy a drink for whoever can do it first.*

*Not actually, sorry.