Chevrolet's largest sedan adds a supercharged performance-oriented version for 2004. Impala comes in base, uplevel LS, and new SS models. All have a V6 engine. The base model comes with a 180-hp 3.4 liter. A 200-hp 3.8 is standard on the LS, optional on the base. The SS has a supercharged 240-hp 3.8. All have automatic transmission and 4-wheel disc brakes. ABS, traction control, and a tire-inflation monitor are standard on the LS and SS, optional on the base. Sport suspension tuning is included on Impalas with the 3.8 V6. The SS is available only in black and comes with 17-inch wheels vs. the other models' 16s. A sport appearance package is newly available for the base model. LS, SS accommodate 5 passengers with front bucket seats. Base has a front bench and seats 6 passengers, or optional bucket seats. A side airbag for the driver is optional on all models. A front side passenger airbag is not offered. OnStar assistance and satellite radio are optional. Added midyear for the SS was an Indy Limited Edition package that includes a boost gauge, special trim, and chrome wheels. Impala shares its basic design with the Buick Century and Regal, Pontiac Grand Prix, and Chevy's own Monte Carlo coupe.