| Building The Ultimate Drivetrain - Project Phoenix Part 7
As a driver in NASA's SE-R cup road race series, I'm used to road racing SE-Rs, but this SE-R is unlike any I've ever taken out to the track or driven. Project Phoenix strikes!
Although the Nissan Sentra SE-R is blessed with the nearly indestructible SR20DE engine, its notoriously weak transmission delayed the car's development. Ever wonder why you don't see more hot SE-Rs racing in Quick Class or many big-powered turbo SE-Rs lurking on the streets? It's not the engine that's lacking. It's the transmission. The transmission is the area where Honda has a major advantage over Nissan.
In last month's edition of Project Phoenix, we covered the basics to get the buttery soft gears and transmission case of the SE-R to live under boosted conditions. Since we're planning to take Project Phoenix into serious battle, we had to take another step; we set out to build the strongest, most bulletproof SE-R drivetrain ever concocted.
PAR GearsetThe Australian company Precision Automation and Robotics (PAR) is known for its bulletproof gearsets for the Subaru WRX, another excellent car saddled by a weak transmission. We approached PAR's North American Distributors, JGY Customs, Inc., to help us obtain one of PAR's gearsets for our SE-R.
The PAR gearset has what's known as a constant mesh engagement instead of the common syncromesh engagement used by most production cars. In syncromesh engagment, cones push into cups to match transmission gear speeds so the gears don't grind during shifting. Syncromesh engagement is smooth and quiet-that's good for street cars, but it's not the fastest way to shift.
Constant mesh transmissions use dogs and dog rings to match gear speeds. Dogs are big, beefy tabs on the backsides of gears, and dog rings are rings attached to the adjacent gear with slots in them. When shifting, the dogs grab the dog rings, instantly spinning the adjacent gear up to speed, allowing the gears to engage. Because of this instant positive engagement, constant mesh transmissions can shift very quickly and positively, normally as fast as you can move the lever.
There are disadvantages to constant mesh transmissions. Engagement is rough (there's a bang) and the shifting is notchy and requires more effort. With a constant mesh transmission, you must shift decisively and with some authority, or the dogs will grind, quickly ruining them. If you can shift accurately, you'll be rewarded with lightning-fast shifts both up and down. For these reasons, all motorcycles and nearly all race and rally cars feature constant mesh transmissions.
For full-throttle, clutchless, lightning-fast upshifts, you simply preload the shifter right before you want to shift and back off the throttle slightly. The transmission will go right into the next gear faster than you can blink an eye. This is especially interesting for drag racers and those with turbo cars. You don't have to close the throttle all the way, just quickly reduce the throttle to unload the gears and witness the fastest speed-shifting ever.
Although this might seem scary to those of you conditioned to years of driving syncromesh transmissions, it's easy, and if you shift with a sharp snap, it's harmless to the transmission.
In the case of the SE-R transmission, the constant mesh engagement has a very important feature; unlike bulky syncros, dogs and dog rings don't take up much room or add much thickness to the gears, which frees space, allowing the gears to be much wider and stronger.
PAR also uses a high grade of steel in the gearsets and a special heat-treating process to ensure toughness. Stock transmissions use a small gear tooth profile to reduce noise at the cost of some strength. The gears also use PAR's super tooth profile, a large tooth profile that gives much more engagement area and strength. Durability, not noise, was a consideration when designing the tooth profile. The gearsets feature straight-cut gears that are slightly stronger than stock helical-cut gears, but are slightly noisier. Straight-cut gears transfer power more efficiently because they don't slide across each other as helical gears do. The transmission will run cooler and soak up less wheel power as a result.
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.
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.
To help the axles deal better with our low suspension and road racing torture, the center bars were shortened to prevent them from bottoming out the CV joints at low ride heights. The cup races were polished for low friction. High-temperature boots were used and the inner boots vented with special tubes to prevent them from inflating at high temperatures and ripping. Special heat-resistant synthetic grease in the CV joints also helps fight the heat.
The Driveshaft Shop says these axles should be good for at least 500 hp, and we feel confident they'll be a huge improvement over the stock Nissan axles.
Volk LE28N Wheels Toyo RA-1 Race TiresFor light wheels, we once again turned to Volk, one of the leaders in the market for lightweight, strong wheels. In road racing, you can drop wheels off the paved surface, hit FIA curbs and strike debris, so strong wheels that can take punishment can give you piece of mind.
Volk let us use a set of its new, lightweight LE28N wheel. The LE28N is lighter than the industry standard for trick light wheels-the Volk TE37-by a few ounces. Forged monoblock construction ensures these will be strong wheels, despite the thin cross section.
I use the TE37 exclusively on my road racecar and I find that they are very hard to bend, even with unintentional 100-mph airborne off-track running. We prefer a wider wheel to keep the rubber flat on the ground. Our 17x7.5-inch wheels had a 43mm offset, and we used a 5mm spacer to make the actual offset 38mm. This fit in Project Phoenix's wheel wells with a bit of fender rolling. Our wheels weighed only 14 pounds, which is extremely light for the diameter and width.
We needed a sticky tire, but it also had to withstand punishment from wheelspin without chunking or greasing out. One of the longest-lasting and most heat-resistant of the current crop of DOT racing radials is the Toyo RA-1.
We've found in testing that the RA-1 also seems to grip decently in a straight line, easily capable of handling 2.2-second 60-foot times. Not bad for a DOT-approved, street-legal tire that can also hang a turn with aplomb. It also had a touring car look that we wanted and is one of few race tires available in 17 inches. We settled for a 205/40-17.
Taking Project Phoenix to the track was an exercise in excess. The car's rapid acceleration and high straight-away speeds made it clear that even our big brakes weren't adequate to slow the car with the soft street compound pads we were using. What we needed were some real race brake pads like Hawk's Excellent Blue Compound.
Project Phoenix was 1 second per lap faster than a modified R32 Skyline GT-R and several seconds per lap faster than a $150,000 Porsche Turbo that was at the track that day as well.
Project Phoenix pounded out lap after lap reliably in high 90-degree temperatures without overheating or blowing up. This is a testament to the soundness of our project car so far. We hope to return to the track soon with better brake pads to really lay the smackdown on some big-name exotic cars.