After some 34 years of continuous improvements of its original design, Porsche's legendary rear-engine 911 was redesigned as an early 1999 model. About 7 inches longer than its predecessor, the new 911 was an inch wider, on a wheelbase 3 inches longer than before. Continuing 911 tradition, the "flat" (horizontally opposed) six-cylinder engine was mounted in the rear, but it underwent considerable change. In addition to switching from air cooling to water cooling, the engine had dual-overhead cams rather than a single-cam configuration, with four valves per cylinder instead of two. Essentially, it was a 3.4-liter version of the engine used in the smaller Boxster, producing 296 horsepower--more than the prior 3.6-liter. Considered the "classic" Porsche, the 911 Carrera first came in 2+2 coupe form with rear-wheel drive. Cabriolet convertibles and Carrera 4 models (with all-wheel drive) joined later. A six-speed manual transmission was standard. Porsche's five-speed automatic transmission, which offered "Tiptronic S" operation using manual-shift buttons on the steering wheel, was an option. Antilock four-wheel disc brakes were standard, as were side-impact airbags. As before, the coupe's back seat was a tiny, minimally useful feature. To a large extent, the 911 was in a class of its own, but rivals included the Acura NSX, BMW Z3 series and more costly Z8, Chevrolet Corvette, and Mercedes-Benz SL-Class. A satellite-based navigation system was optional.