The S12's aftermarket selection during its time of production and the years following it's release was very limited. The S12 was overshadowed by other Nissan models at the time such as the Skyline and 300ZX, which were more popular models to modify and tune. There were a handful of manufacturers who produced parts for the S12 chassis, these can be seen in the following page…

Hoshino IMPUL Co. released a series of body parts in 1984 for the Japanese Market MKI Silvia and Gazelle. The lineup consisted of a front lip, one-piece side skirts, rear underskirt and a rear spoiler.

MAD (Max Air Dynamic) “Fashionable car accessories produced by YAC”

In 1984 MAD Japan released a number of aero body parts for the MKI Nissan Silvia/Gazelle. The catalog showed a MKI Silvia RX-E hatchback wearing the full kit consisting of front bumper, rear bumper, side skirts, rear wing and rear under-spoiler.
These body parts were also distributed into the North American market under the Erebuni brand name.

Parts List:

MAD-23 Front Bumper Spoiler

By installing a newly designed bumper-body spoiler on top of the genuine bumper, it cuts the airflow flowing into the underfloor, reduces the air field (L) and resistance (D), and improves high-speed performance and high-speed stability.

MAD-24 Side Protector

By significantly reducing the amount of crosswinds that enter the under floor, we have improved cornering performance at high speeds.

MAD-25 Rear Bumper Spoiler

It improves streamlining effect from the body underfloor and prevents mud from being kicked up by swirls in rainy weather. It uses the ground effect mechanism used in new racing cars to create a venturi effect, increasing downforce and working together with the front spoiler to improve high-speed stability.

MAD-26 Rear Under Effect Spoiler

By adding it to the rear bumper spoiler, the rear streamlining effect is improved and the ground effect mechanism is utilized.

MAD-27 Rear Modulated Spoiler

This is a large, newly designed spoiler that achieves the ideal airfoil shape required for hatchback vehicles and generates ideal downforce.

The MAD demo car on the cover of Option Magazine, February 1984.

NISMO (Nissan Motorsports International) released two engine-specific strut braces for the S12 chassis. One for the FJ20 found in the MKI Silvia & Gazelle Turbo RS-X, and another for the CA18DET found in the MKII Silvia RS-X. The contours of the strut brace centre piece were shaped to fit over the intake manifold and valve covers of both these engine variations.