Project S13 - Part 3: The Good Stuff

According to Nismo, the designed engine torque capacity of the five-speed and S15 Silvia Spec R six-speed is 217 lb-ft of torque, and the capacity of the Nismo six-speed is 289 lb-ft of torque, thanks to gearing and gear diameter changes.

According to Nismo, the designed engine torque capacity of the five-speed and S15 Silvia S

Nismo reinforced six-speed transmission swap
Installation location: SR Motorcars inGardena, Calif.Time: Four hours, not counting the burgers

The reason we went with an S15 clutch is because while we were at JDM Power, we also picked up the holy grail of Nismo parts: the Silvia/180SX reinforced cross six-speed transmission. Many S13 and S14 240SX parts swappers have dreamed of having a six-speed transmission behind their KA24DE or SR20DET engine. The only previous option was to swap in the stock transmission from an S15 Silvia Spec R or one of the special six-speed Autech S15 Silvias. But that route has its own issues because the S15 six-speed doesn't have a mechanical speedometer drive gear inside the transmission casing like the five-speed S13, S14, and S15 Spec S models do. The S15 Spec R picks up its speedometer signal electronically from the rear ABS sensor, so an S15 six-speed transmission swap necessitates a swap to the rear S15 pumpkin and lots of custom wiring to get the S15 gauge cluster to work (the S13 and S14 gauge clusters will not read the S15 speed signal). So, unless you're truly dedicated or don't care to know how fast you're going down the street, an S15 six-speed transmission is not a direct bolt-in option for any U.S. 240SX.

The Nismo reinforced six-speed requires a switch to an S15 clutch assembly. Notice the depth on the aluminum flywheel. This sits the clutch out much further, compared to stock, and compensates for the six-speed's input shaft location.

The Nismo reinforced six-speed requires a switch to an S15 clutch assembly. Notice the dep

This is where Nismo steps in. Starting with the FS6R92A S15 six-speed transmission casing, Nismo fits a custom reinforced gearset and adds a mechanical speedometer drive gear to the mix. Nismo reinforced six-speed transmissions come fully assembled from JDM Power so we didn't bother tearing the gearbox apart to cryo-treat or coat the gears. JDM Power sells the complete Nismo bolt-in kit, which also includes the transmission mount, driveshaft, shifter, hardware, and required harness extensions. The only other items you'll need are an S15 clutch, new shift knob (five-speeds use a 10x1.25 thread, six-speeds are 12x1.25), and gear oil. Unhappy with all the burning hot aluminum and titanium shift knobs on the market, we had our rubber Nissan shift knob machined out to 12mm.

Nismo offers the reinforced six-speed transmission with a multitude of kits to make it a direct bolt-in installation into any S13, S14, or S15 equipped with an SR20DET or SR20DE engine. If you own an S13 or S14, you'll need to swap over to an S15 clutch at the same time just like we did because of the difference in reach between transmission input shafts. The S15 flywheel, pressure plate, and clutch will directly bolt on to any SR20DET engine.

Barely visible from the outside is the speedometer drive gear in the Nismo six-speed transmission. With this feature, the Nismo unit becomes a direct bolt-in swap. S15 Silvia Spec R models don't have this gear and require a lot more hoops for S13/S14 owners to jump through.

Barely visible from the outside is the speedometer drive gear in the Nismo six-speed trans

We paid a visit to Steve Rodgers at SR Motorcars in Gardena, Calif., and swapped out our tired five-speed transmission in less than half a day. Rodgers knows the S chassis and SR20DET engine inside and out and made short work of the installation after lifting the transmission into place with a Herculean effort. We were pleasantly surprised to discover just how simple Nismo has made this six-speed swap. All parts are labeled, separately bagged, and have perfect clearances. The included driveshaft was the perfect length and had zero balance or vibration issues. After we fired up the car, it was ready to go and the speedometer functioned perfectly. This is what you get with near OEM-level engineering.

Because it's based around a standard S15 six-speed transmission, shifter feel is largely the same as with a stock S15 Silvia Spec R. The throws are quite long for performance use but the precision is what matters and the six-speed shows its strength over the five-speed there. Shifting is much more precise through the gears and the movement is so smooth, there isn't any need to bang or shove gear changes.