The Mustang lineup now includes Mustang and Mustang GT models, both offered in base or Premium trim, along with the high performance Shelby GT500. All models are offered as either a coupe or convertible. Both body styles are four-passenger coupes, though the back seat is only fit for smaller occupants. Convertibles get a power-folding soft top that, does not take up additional cargo space in the trunk when stowed. A new glass roof can be added to coupe models featuring special glass that brightens up the interior yet blocks infrared rays. A retractable blind system is included. Standard Mustang models have respectable performance from a 4.0-liter single-overhead-cam V-6 engine making 210 horsepower and a stout 240 pound-feet of torque, while the Mustang GT upgrades to a more spirited 300-horsepower, 4.6-liter aluminum V-8. Both engines come with a standard five-speed manual transmission or optional five-speed automatic transmission. With MacPherson struts in front and a three-link rear suspension with Panhard rod, the Mustang has a comfortable ride and impressive handling despite the old-style solid-rear-axle configuration. All Mustang models get four-wheel disc brakes, but GT models upgrade to larger brakes with twin-piston aluminum calipers in front. Anti-lock brakes are standard in all but the base model. Side airbags are standard across the line. The base Mustang comes with a long list of standard features, including cruise control, keyless entry, air conditioning, power windows and locks and a CD sound system. Base GT models come with similar equipment but add fog lamps, anti-lock brakes, larger alloy wheels, and a power-adjustable driver's seat. Premium models add a Shaker 500 audio system with six-disc changer and MP3 compatibility, Sirius satellite radio, ambient lighting and various interior upgrades, including a satin aluminum instrument panel, ambient lighting, and special trim. Premium GT models get sport leather bucket seats. The options list is extensive, with several packages adding a distinctive look and feel to the Mustang. The Bullitt Package brings cold-air induction, a sport suspension, aluminum trim inside, and a host of other upgrades, while the GT California Sport Package brings leather bucket seats, a chin spoiler, side scoops, and bright exhaust tips among other things. Standalone options include a DVD-based navigation system and the Shaker 1000 premium sound system. The Shelby GT500 pushes the performance up to the levels of an exotic sports car, adding a 500-horsepower, 5.4-liter supercharged V-8, six-speed manual transmission, a limited-slip differential, a performance-tuned suspension, Z-rated tires, Brembo brakes, a special exhaust system, and a lot of interior extras such as the Shaker 500 audio system, HID headlamps, and sport seats.