By TOM KRISHER
AP Auto Writer
DETROIT (AP) - Back when gas was cheap, Americans bought cars with V-8 engines like the Big Block, Cobra Jet and Ramcharger. Acceleration was all that mattered, even in family cars that never made it to full throttle.
The 427-cubic inch Chevrolet Tri-Power was the siren song of the gearhead, sending Corvettes roaring down the highway at up to 140 mph.
But now, thanks to government regulation and gas-price gyrations, the motors that move the nation's cars and trucks are shrinking.
Whether they drive hulking pickups or family sedans, Americans are increasingly choosing smaller engines that use less fuel, especially four-cylinder models that offer more horsepower than was possible just a few years ago.
More than half the new cars and trucks sold in the U.S. through May had four-cylinder motors. That's up from 36 percent in 2007, and it's the highest sales percentage since 1998, when the J.D. Power and Associates consulting firm started keeping track.
The smaller engines are helping to change America's gas-guzzling ways. The government now requires automakers to build more fuel-efficient cars and trucks. Drivers are eager to save money on gas, which recently flirted with $4 a gallon and is still pricey at an average of $3.53. Also, people have embraced cars with downsized engines because new technology has made them just as fast as older cars with bigger motors.
"You can take away my V-8, but don't take my acceleration," said IHS Automotive analyst Rebecca Lindland. "We're willing to embrace a technology that doesn't make us compromise performance."
In general, car shoppers can pick from three types of engines: four-, six- and eight-cylinders. More cylinders usually produce more horsepower but also burn more fuel.
Until recently, each engine type had dedicated fans. Pickup drivers, who tend to haul heavy loads, favored brawny V-8s. Sedan drivers generally opted for six cylinders if they wanted snappy acceleration or four cylinders if they preferred fuel savings.
Decades ago, when gas was cheap, buyers usually went for bigger engines to get more power. Back then, noisy "fours" clattered down the highway inside compacts or wimpy midsize cars. Some drivers complained that four-cylinder cars didn't have enough power to merge safely onto busy highways.
That began to change in the 1990s, when Honda and Toyota refined their fours, making them quieter and more powerful. In 2005, gas prices spiked after Hurricane Katrina knocked out refineries. The steeper prices made fuel-efficient cars more popular and forced Detroit's truck-obsessed automakers to spend more money improving their smaller engines.
Small engines got another boost in 2007, when the government began raising gas mileage minimums, eventually requiring new cars and trucks sold in the U.S. to average 54.6 mpg by 2025. The shift toward smaller engines gathered more momentum in 2008, when gas spiked again _ above $4 a gallon.
Because of technology advances, many four-cylinder engines are more powerful than V-6s from only a few years ago. For example, today's Hyundai Sonata midsize car has a 2.4-liter four with 198 horsepower, 45 more horses than the base V-6 in a 2006 Ford Taurus.
Mileage was important for Meagan Sherwood of Milan, Mich., when she bought a new four-cylinder Hyundai Veloster. The property manager traded a V-6-powered Jeep Wrangler for the funky hatchback, which gets up to 32 mpg in city and highway driving. The Jeep, she says, got around 13.
"I was filling up twice a week on a 15-gallon tank with the Jeep," Sherwood said. "Now I fill up once a week with a 10-gallon tank."
Sherwood said she would only go back to a larger engine if she and her husband start a family and need more space.
To boost the efficiency and power of small engines, companies have introduced all kinds of technology:
_ Direct fuel injection is more common. It mixes air and gas in the chamber that surrounds the piston, helping produce more power, more efficiently.
_ Many small engines now have turbochargers, which force high concentrations of air into the piston chamber, allowing more gas to be sent in and offering extra acceleration or hauling capacity whenever drivers step on the pedal.
_ Engineers have made cars more aerodynamic. Also, some vehicles shut off their engines automatically at stoplights. They can run pumps and other devices off the battery rather than a belt that sucks power from the engine.
Even as they become more powerful, smaller engines are helping lower gas consumption. So far this year, consumption is down 5 percent from the same period a year ago, according to government data.