The guys at Technosquare installed our Nismo diff while the transmission was apart for the gearset install. Our driving impressions of the diff were very positive. Instead of uselessly spinning the inside wheel on the exit of corners, Project Phoenix now spins both wheels getting more acceleration out of corners. This great improvement in forward drive also helped bring the car out of oversteer faster. When both wheels spin, the car is instantly pulled out of oversteer. Overall traction is much improved. Previously it was easy to spin gears one through three, and sometimes even fourth!
With the Nismo diff, wheelspin was mostly limited to one through two, and occasionally third gear, even when running 20-plus psi of boost. We also enjoyed the ability to trail brake deeper into turns without worrying about inside wheel lock-up. Turn-in was not affected and understeer was not increased.
Tire life also improved 50 percent on our powerful turbo car when it was driven on the track. The only negative thing we felt was an increase in torque steer for the car's first track session. This disappeared in just a few minutes of track driving as the differential broke in. In a turbo car, this differential is a huge improvement over the stock viscous unit.
If your 1998 SE-R, 1990 to '96 G20 or 1998 to '99 Sentra SE didn't originally have a limited slip, Nismo also carries a differential that can convert your non-LSD transmission over to one of these units. Previously, the transmission cases weren't compatible between limited-slip and non-limited-slip differentials so if you wanted a limited slip, you had to change the whole transmission and the axles, an expensive proposal. Now, you can have a superior limited slip for a lot cheaper and with fewer hassles than previously seen.
Jim Wolf Technology Dual-Disc Clutch
Dual-disc clutches offer twice the friction surface of a single disc. This enables less pressure plate clamping force to get the job done so your leg and thrust bearing can breathe a sigh of relief.
Dual discs can often get away with a smoother, less aggressive friction material for longer life and smoother action. They can be made with a smaller diameter that greatly reduces inertia, allowing the engine to accelerate much more rapidly.
Dual-disc clutches also have a smaller diaphragm spring and no Marcel spring under the friction material, making for a short engagement travel. The short engagement travel can make starting off a bit difficult but, combined with the light overall weight, ensures fast shifts.
JWT's dual-disc clutch reeks of trickness. Its small, 7.5-inch diameter means low inertia; we calculate it at 16 times less rotating inertia than the stock clutch and flywheel. The small clutch assembly is bolted to a thin billet-aluminum flywheel, which couples the clutch to the starter. The entire assembly weighs only 14 pounds. This is several pounds less than the weight of just the stock flywheel alone.
The pressure plate and basket are machined from billet aluminum and contain the diaphragm springs and the discs. The large surface area of the dual discs allows the use of a nonaggressive organic friction material. This means the pressure ring and floaters of the pressure plate, as well as the friction surface of the flywheel, will have a long life. It also means the clutch will have a relatively smooth engagement, despite the full race nature of this clutch. Dual-disc racing clutches with metal linings are just about unstreetable because they're so grabby.
JWT's SR20 combination has been torture tested on a 600-plus-hp 9-second SE-R with good results, the clutch taking off several tenths from the 60-foot time. The clutch had an exceedingly light pedal pressure and a relatively smooth engagement, although the short engagement travel took a little while to get used to.
Once we did, our quick-shifting PAR gearset was even quicker shifting. The engine is incredibly responsive, revving instantly with a touch of the throttle, like a sportbike. When driving, the throttle response due to the low inertia and light weight is amazing.
We punished the clutch with a few laps around the Streets of Willow road course at 23 psi of boost, punishment perhaps worse than multiple dragstrip passes. The clutch held well; it never hinted of slipping.
On the street, it was manageable in bumper-to-bumper traffic, not killing our right leg and not getting on our nerves excessively. This is probably the most streetable super-high-capacity clutch we have driven to date.
Driveshaft Shop Axles
To help stop axle problems before they occur, we contacted The Driveshaft Shop for help. Its Stage II axles, with a few modifications, are better suited for road racing for us.
The axles feature hollow 4340 chrome-moly center bars that have a special inert gas heat-treating process with a post-heat-treat double temper. This toughens the axles but still leaves them ductile. The center bars can twist with up to 10 degrees of rotation, giving the drivetrain some cushion, just the thing for the weak SE-R tranny. The CV joint cups and races are heat-treated to give them good surface hardness, but not make them brittle. The CV joint parts and center bars are shotpeened after heat-treating to improve their fatigue strength.