OS Giken Nissan Skyline, GT-R and Z32 5-speed close ratio gearset
OS giken close ratio gearset for 5W30A gearbox in BNR32 and BCNR33 GT-R, ECR33 GTS-T and ER34 Skyline GT-T turbo and Z32 300ZX twin turbo, 5-gear kit including input shaft.
OS Giken close-ratio gearsets offer greatly increased gear strength, along with closer gear ratios to suit racing applications. The retention of normal synchromesh parts and a helical gear design means the gears are still almost as quiet as a standard gearset, so this is an excellent upgrade for street-driven vehicles too. As you can see by the numbers below, you get a taller first gear, so second and third are much closer together. Fifth is also lower to improve acceleration in this gear.
OS Giken ratios: 2.695, 1.703, 1.236, 1.000, 0.826
Standard ratios: 3.214, 1.925, 1.302, 1.000, 0.752
This gearset is designed for the final 1997 version of the BCNR33 GT-R gearbox, or ER34 gearbox, some additional Nissan parts will be required to update earlier versions of the FS5W30A (Z31).
The gears are rated at 1200ps, so they are suitable for most modified RB engines. The limiting factor is the Nissan synchros. While the latest version of the synchros is used, they may still fail if shifting too fast at over 9000rpm. For this reason extreme drag car applications should look at the OS-88 sequential gearbox. That said, this gearset has been used successfully in a number of 9-second GT-Rs.