If you're concerned about noise, PAR can make helical gears by special order. The PAR gearset replaced gears one through four, keeping the stock fifth gear. We wanted to do this because fifth gear breakage is uncommon and we wanted a quiet fifth for freeway cruising. PAR can make specially ordered one-through-five dog gearsets for hardcore racers.
For assembly of our transmission, we turned to our buddies, Richie and Howard Watanabe, at Technosquare in Torrance, Calif. If you live in the Southern California area, Technosquare is the best damn garage in town. From racecar prep work to fabrication, the Watanabe brothers are amazingly fast, accurate and reasonably priced.
The PAR gearset fit right into the stock SE-R transmission case. In our case, we didn't need to reshim our case to set proper endplay as the PAR gears neatly matched our gears. PAR says its gearset can hold up to 500 hp, which is more than twice the capacity of the stock gears.
Once assembled, we were amazed at the fast upshifts and downshifts. The gears had a slight whine to them, but we think it's a cool noise, sort of like half the volume a gear drive in an old-school small-block Chevy would make.
Some people might find constant mesh shifting taxing in daily driving. For those who need smooth stock-like shifts, PAR is working on a syncro gearset that may be available by the time you read this. The syncro gearset will feature superior materials and PAR's super tooth gear profile with the widest gears possible. The syncro gearset is being designed to hold more than 400 hp, still twice the power of what the stock SE-R transmission can handle.
Distributor JGY Customs, Inc., not only keeps PAR gearsets in stock, but can also handle transmission prep work and assembly as well. Even with these strong gears, it's still important to do the case welding, run Redline Shockproof heavy gear oil and use the stronger motor mounts for your transmission to have a long life.
At this time, it's also a good idea to change all of the bearings and seals as well. Courtesy Nissan's mail order division supplied our OEM parts.
Nismo Limited-Slip Differential
The stock viscous coupling limited-slip differential leaves a lot to be desired. The stock differential quickly wears out and acts like an open differential. The viscous silicone goo in the differential doesn't offer much in the way of a positive coupling, giving only light limited-slip action. It's common to see an SE-R doing a one-wheel burnout at the dragstrip because of this and road racing SE-Rs often do one-wheel burnouts at the exit of corners. Flexing a powerful turbo motor greatly exaggerates this. This can really slow down an SE-R in both road and drag racing
To combat these problems, we installed a Nismo limited-slip differential. The Nismo differential is a mechanical 1.5-way differential. Instead of relying on goo to transmit torque from one wheel to another, it uses mechanical clutches preloaded by spring washers that are calibrated to an initial breakaway torque.
The Nismo diff's initial breakaway torque is set at 8 kg/cm, but it can be reduced to 2 kg/cm by re-orienting the clutch discs inside the case if less limited-slip action is desired.
The Nismo diff is called a 1.5 way because of a mechanism that causes the differential to lock up harder if one wheel starts to spin at a higher or lower rate than the other. The shafts the pinion gears ride on have a cam ground into their ends. The cams ride in holes in-between two drums that slide inside the differential case. If one wheel starts to spin, the torque is applied to the pinion shafts and the cams, which tries to push the drums apart and applies more load to the clutch packs. This causes the clutch packs to grip tighter and forces both wheels to turn together.
The Nismo diff is a 1.5 way because it can lock up the differential fully going forward and halfway going backward. The shape of the cams on the pinion shafts and the holes that they ride in between the clutch drums determines the 1.5-way action.
The action is important in a FWD car. If the diff is a two-way, then the car will resist turn-in and understeer too much. A 1.5 way allows some torque transfer under deceleration and braking. This is good because it helps prevent inside front-wheel lock-up under hard braking and cornering conditions that you find often in road racing.
Finally the stock differential only has two pinion gears. Although it is not common to break these, it has occurred before, especially in SE-Rs that are drag raced. Since all of the engine's torque is transferred through these walnut-sized hunks of metal, the Nismo unit has four pinion gears, twice the amount.