Project S13 - Part 3: The Good Stuff

Nismo claims to have reinforced this transmission over a stock S15 six-speed through the use of larger-diameter gears and by changing most of the gear ratios versus the standard S15 box. For Fifth gear, which is the same as the standard S15 (1.000), Nismo has reduced the number of both counter and main gear teeth and has increased the size of the gear teeth. First gear for Project S13 is now noticeably taller (numerically lower), with the new gearing helping to cushion the launch shock load from a standstill. One of the biggest advantages with the Nismo six-speed though is how Second, Third, and Fourth gears have all been moved closer to each other, which helps us stay above the boost threshold when on track.

Nismo GT LSD Pro
Installation location: SR Motorcars inGardena, Calif.
Time: Two hours, counting the pictures

The Nismo GT LSD Pro kit includes everything you'll need for installation-new OEM differential bearings, a pumpkin cover gasket, and bolts. Be sure to get a more synthetic 80W-90 oil for the fluid change after break-in.

The Nismo GT LSD Pro kit includes everything you'll need for installation-new OEM differen

When it comes to 240SXs, a limited-slip differential is a must. Look at it this way: when Project S13 goes around a corner, its rear wheels travel in two different arcs and thus the two wheels are moving at different speeds. With an open differential, the same amount of torque is distributed to both wheels at all times and as you corner harder and one tire begins to lose traction, that tire will go up in smoke and continue to do so unless you ease off the gas. As the tire spins into dust, that wheel is exhibiting a much higher wheel speed than the wheel opposite it. The problem with this is that the non-spinning wheel, with grip, will ultimately be fed the same low amount of torque that the spinning wheel is capable of holding.

A limited-slip differential limits the difference in wheel speed between the drive wheels by diverting torque from the spinning wheel over to the non-spinning wheel. This allows you to take advantage of a greater overall level of grip and to play more with the slip angle of the rear tires, allowing a driver to easily adjust the balance of the car using the throttle.

The Nismo limited-slip differential even comes with new, proper stub axles, which will eliminate any headaches about having the wrong parts. You will, however, have to be sure to get the correct fitment for your S13 depending on if it has five or six bolt axles.

The Nismo limited-slip differential even comes with new, proper stub axles, which will eli

For Project S13 we wanted a limited-slip differential that was responsive and provided a smooth, easy breakaway at the limit. We again contacted JDM Power, this time for a Nismo clutch-type limited-slip differential. They then told us about the GT LSD Pro. Clutch-type differentials work by using springs that apply an "initial torque" to the clutch plates found within the limited-slip differential itself. As one wheel begins to spin more than the other, it locks the clutches together, transferring power to the opposite wheel. A higher initial torque value or tighter clutch pack will allow less speed differential between the wheels, locking the wheels together sooner. Drifters will often use a higher initial torque value than road racers because they actually want their cars to kick out soon after applying the gas during cornering.

Unique on the market, the GT LSD Pro features an externally adjustable initial torque setting. The standard Nismo GT LSD makes use of 20 clutch plates to help smooth over the locking transition. The GT LSD Pro then adds three grooves of different depth to its pinion mate shaft, which is connected externally to a 19mm head. By unbolting the right side axle and popping off the stub axle, a ratchet and socket can be inserted to turn the pinion mate shaft left (47.0 lb-ft initial torque), center (61.5 lb-ft), and right (101 lb-ft). With this capability, the limited-slip differential can be set trackside to compensate for power, tires, or even the difference between a drift day and a track day.