With stop-start, the car's engine is shut off when the vehicle is stopped and the driver applies the brakes. Releasing the brakes and touching the accelerator fire up the engine.
The problem: The EPA city-mode test cycle includes only one complete vehicle stop, so stop-start technology registers only a 0.1- or 0.2-mpg improvement, Davis said.
Since stop-start costs money to install, there's no marketing magic that will persuade people to pay the extra $500 Mazda would charge for the fuel economy gains that the EPA says don't exist.
"In Japan, we're seeing anywhere from 7 to 9 percent fuel economy gains from it," Davis said. "That's a jump from 33 to 37 miles per gallon in a metro environment."
He said Japanese consumers are so smitten with the technology that Mazda is selling nearly half of its Axela (Mazda3) and Biante (a small van) units with stop-start.
Relief could be on the way. The EPA is taking public comment on rule changes that could give cars with stop-start higher fuel economy ratings. A decision is expected in April.
Because the EPA is seeking input on its rule-making standards, Davis wants a united lobbying effort for a testing procedure that recognizes the benefits of stop-start.
Davis' pleas are obviously in Mazda's interest, but Mazda is far from the only automaker wanting to bring stop-start technology to the United States.
Volkswagen put start-stop in its Lupo hatchback in 1999, as part of its astounding 75 mpg rating. Since then others have developed systems -- mostly with diesel applications -- but have chosen not to offer them to U.S. customers for the same reason Davis outlined.
Mercedes-Benz has said it will have start-stop available on all engines by 2011 but has made no commitment for this market. This year Hyundai announced plans to bring start-stop to the United States but did not say when.
Audi of America spokesman Christian Bokich said: "We did not realize any savings in U.S. EPA estimates based on required testing cycles."