WAGON, WHOA! The engine in Audi's new A4 Avant is a prize winner.

Byline: J.P. VETTRAINO

The 2009 Audi A4 Avant is very easy to like. It is compact but comfortable, versatile and available with nearly any gizmo you might need to entertain yourself. It's satisfying to drive, wagon roofline be damned, and it's good-looking to boot.

Beyond that, it's not our purpose to promote the intrinsic rationality of good station wagons. Rather, we come with news of the little gem under the A4 Avant's hood. It's an easy engine to like-regularly seen on various "best engine'' lists in previous iterations and now better than ever.

While the all-new A4 sedan offers several powertrain variations, the small-volume wagon has only one: six-speed ZF automatic transmission, quattro all-wheel drive and the latest evolution of Audi's 2.0-liter turbo with gasoline direct injection. We'll see more of this inline-four in other Audis and Volkswagens soon, starting with the long-anticipated 2009 Audi TTS.

Audi calls its turbo/direct-injection technology TFSI-a concept first applied in 2001 on the Le Mans-winning R8 prototype for its combination of output and fuel efficiency. The company's original 2.0 TFSI was the first such production engine offered in North America, completing a century-long quest to move the point where fuel feeds into an engine closer to the point where it burns. Compared with familiar port injection, direct gasoline injection spits fuel directly into the combustion chamber under intense pressure-about 2200 psi in the 2.0 TFSI-and intensifies the swirling, evaporative effect.

Direct injection is often touted for its fuel efficiency, because it allows an engine to run leaner than conventional injection, but that's not the only point in the 2.0 TFSI. Direct injection burns cooler, which is the primary reason it can run leaner, and that allows a turbocharged gasoline engine with much higher compression than we've seen in the past-10.5:1 in the 2.0 TFSI. The compression ratio further improves thermodynamic efficiency and enhances the output/fuel-consumption ratio. Higher compression also allows better response before boost builds and creates exhaust pressure faster to reach full boost fractionally sooner.

Improvements to the new 2.0 TFSI start with the water-cooled turbocharger. The turbine and compressor wheels have been refined to improve response time. A "blow-off'' valve keeps the boost chamber and induction tube pressurized when the driver lifts and decelerates, so there's no waiting around for the turbo to spool up when it's time to get back on the gas. The intercooler is smaller and lighter, with the same charge-cooling efficiency as in the previous generation.