"Spec-R

The Spec-R differed from previous Silvia models by featuring a 6-speed manual transmission. The Spec-R also included extensive chassis and suspension strengthening via the use of larger anti-roll bars and strut bracing. The S15 featured the same 4-piston front brake calipers that were found in the Z32 300zx but included a larger brake booster.

One of the biggest changes to the S15 model of the Silvia fitted with the 6-speed manual transmission built by Aisin AI was the implementation of a helical limited slip differential. The result was a safer, more track suited drive; in some contrast to its drifting heritage and subsequent media attention. All other versions of the Silvia (S14, S15 Spec S JDM) came with the viscous limited slip differential.

As with many Nissans, HICAS (High Capacity Active Steering) four-wheel steering was available as an option."

https://en.wikipedia.org/wiki/Nissan_Silvia