In 1999 the latest version of the popular Silvia lineup was released, the S15. The upgraded turbocharger and software changes meant large performance boosts from the SR20DET engine. The upgraded styling was also a welcome change, bringing the Silvia line right in to the modern design age. The S15 was available in turbo, and non-turbo models.

Spec-R featured a 6-speed manual transmission, strengthened chassis/suspension, and larger brake boosters. A key feature was a new helical LSD, that made it an attractive track car.

The Spec-S was equipped with a 5-speed manual transmission (same 4 speed auto transmission as Spec R), SR20DE engine, a less rigid frame than the Spec R models, viscous LSD, and 2-piston brakes (again, smaller than the Spec R).

Like the S13/S14 Silvia/180SX, the aftermarket world is overflowing with parts for the S15 SR20DET. With the numbers of S13's dwindling, the S14 is now taking its place as #1 tuning base car. The S15 will take its place in the near future with a drop in prices for them in the used market. They can be seen in various genres of tuning culture, from the Circuit, Drag, Top Speed, LUX/DUB style and of course, Drift. The S15 SR20 is nearly identical to its S14 predecessor except for minor changes in engine and turbocharger specs, giving the S15 a 250ps rating from the factory. Higher flowing injectors and a larger fuel pump gives the S15 engine potential to hit the 300ps mark with a Boost-Up tune.

http://en.wikipedia.org/wiki/S14_Silvia#S14