You don't see this very often: a car company dropping a V-8 engine from a performance car and replacing it with a V-6. But German automaker Audi does it in its 2010 S4 compact sedan.

The move not only creates a more fuel-efficient vehicle during these times of concern for the environment and oil supplies. It keeps performance because the 3-liter, double overhead cam V-6 is supercharged, has direct injection and 333 horsepower. This is just seven horses shy of the 340 horses in the V-8-powered predecessor S4.

The change for 2010 also allows a lower S4 retail price _ all the way to $46,725, including manufacturer's suggested retail price and destination charge. At that price point, buyers get a base model with six-speed manual transmission, standard all-wheel drive, sport suspension, sunroof, leather seats, three-zone climate control and Xenon headlights.

The price is an attractive midway point for buyers of compact, luxury sedans who want a sporty edge.

A BMW 335i sedan with twin-turbocharged six-cylinder engine had a starting retail price of $41,125 for the 2009 model year and produced 300 horsepower. A 2010 BMW M3 with 414-horsepower V-8 starts at $56,975.

The 2010 Mercedes-Benz C350 with 268-horsepower V-6 starts at $40,625, while a 451-horsepower 2010 Mercedes C36 AMG starts at $58,225.

The latest S4 is the performance version of Audi's best-selling sedan, the A4, and it also serves as an entry sporty sedan for the brand. So it's best that it's not too far out of reach, financially, for upwardly mobile buyers.

Company officials have said that the old S4 _ offered as a convertible as well as sedan in the past _ accounted for just 5 percent to 6 percent of U.S. sales of the A4 line. They're hoping for more like 15 percent for the lower-priced S4, which is available in 2010 as a sedan only.

If the test vehicle, in bright red paint and mostly black interior, was any indication, buyers will get a car that has personality galore. It was spirited, right out of the garage and down the driveway. A little nudge of the accelerator while I was in first gear pushed my head back into the head restraint.

Yes, that's healthy torque that peaks at 325 foot-pounds at 2,900 rpm.

With six-speed manual transmission, I roared past other cars on the highway and moved around double-parked cars in the city without effort. In fact, Audi said its tests show the V-6 S4 goes from standstill to 62 miles an hour in 5.1 seconds, which is 0.1 second faster than the heavier S4 with V-8.

Yet, when I wanted a more leisurely ride, I upshifted and let the S4 move at a sedate pace without fuss.

Fuel economy is up some 25 percent in the new sedan, thanks to an engine with two fewer cylinders than the V-8.

The tester, for example, was rated at 18 miles per gallon in the city and 27 mpg on the highway. I was lucky to get 20 mpg in the test drive because it was so easy to tap that low-end power.

The ride was firm, to be sure, and I felt vibrations of road bumps nearly all the time. Continued...