What Does 'S550' Mean On A Ford Mustang?

S550 on the Ford Mustang is the designation of the platform on which the sixth generation is built. The S550 identifies this platform as a front-engine, rear-wheel drive platform used for the company's sports cars, of which the Mustang is the sole nameplate. The S550 platform underpins Mustang vehicles made from the 2015 model year through the 2023 model year. 

The S550 platform brought several innovations to the Mustang. The most important was independent rear suspension, the first time this had been done in a mass-produced Mustang. Replacing the previous generation Mustang's live rear axle meant a greatly improved ride and better handling. In the front, the MacPherson strut suspension was also new. Another improvement over the previous generation was a 28% more rigid chassis. The changes extended to the convertible version, which received an improved top with more sound insulation, and a faster-operating top mechanism. 

There were also power upgrades, to add to the ride and handling improvements. The S550 Mustang started out in 2015 with three engine options — a base 3.7-liter Duratec V6 with 300 horsepower, a new 2.3-liter Ecoboost inline four with 310 horsepower, and the Mustang GT with 435 horsepower, powered by Ford's Coyote engine. Power upgrades were made over the life of the S550 platform; the EcoBoost four received a torque boost, the Coyote V8 went up to 460 horsepower, while the V6 was discontinued altogether.

There were several notable models of the S550 Mustang released during its nine model-year run. One of the most special was the 2015-20 Shelby GT350 and GT350R, powered by naturally-aspirated, flat-plane V8 engine putting out 526 horsepower with a redline of 8250 rpm. A flat-plane crankshaft is typically found in engines made for exotic cars, or in racing applications, but this was Ford's first use of it in a production car. 

The 2015-20 Shelby GT350 models also featured braking and handling enhancements, including cross-drilled brake discs with six-piston Brembo calipers at the front, a wider front track, super-responsive MagneRide shock absorbers, and stiffer 19-inch alloy wheels shod with Michelin Pilot Super Sport tires made specifically for the GT350. 

Another fan favorite S550 Mustang was a new version of the Bullitt Mustang, a callback to the Mustang driven 50 years earlier by Steve McQueen in the movie "Bullitt." The Bullitt Mustang was an enhanced Mustang GT, with an additional 20 horsepower from its Coyote V8, thanks to the intake manifold and performance exhaust used on the GT350. 

The S550 Mustang was also the first Mustang to go global, with Ford's ponycar being shipped to Europe and China, as well as versions built with right-hand steering for markets like Japan, Australia, and the UK. The S550's EcoBoost four-cylinder engine was used as the base engine for Europe, where the high cost of fuel is a consideration.