Project 240SX – Part 4 – Bolt-In Nismo Reinforced Six-speed Transmission

One great phenomenon that occurs when you purchase a car that your significant other won’t ever understand is satisfaction. Change out sloppy bushings for fresh ones and you’ll swear you just re-engineered the new GT-R. Swap out shocks for units that actually don’t leak precious fluid and you’ll be happy track day after track day. The difference when improving an old chassis is so dramatic, you’ll actually feel like you’re getting a huge improvement for your money. And you know what, you really are.

We’ve already laid down the groundwork for Project 240SX by putting a solid new suspension into place. After fitting TEIN’s latest monotube Mono Flex coilovers, SPC adjustable rear control arms, Energy Suspension bushings and some custom alignment modifications by M1 Fabrication & Development, Project 240SX drives straight and feels more solid than it ever did in the 1980s. We’ve got a brand new Garrett GT2871R turbocharger waiting to go on to our SR20DET but power is easy to make with a turbo engine and balance has to come first.

One of the most often overlooked areas of modification in project cars is the drivetrain. When you’re hammering up and down through the gears at the track or through the undulating hills of a local back road, the clutch under your left foot and the lever in your right hand matter as much as anything else. Put together a good system and you’ll be too busy chasing short straights and tightening turns to notice. Drop in a few pieces of junk and you’ll be cursing the imprecise feel or shocking engagement point as you careen off the road.

Like you, we enjoy driving more than carrying out R&D. So we decided to get it right the first time around and went with one of the most reputable names in Nissan tuning, Nismo. Short for Nissan Motorsports International Co., Ltd., Nismo is the tuning and racing arm owned by Nissan. From within their Tokyo headquarters, Nismo maintains a Super GT GT500-class program and produces some of the most extensively engineered and tested aftermarket go-fast parts. This includes camshafts, reinforced oil pumps, suspension arms, brakes and limited-slip differentials.

Nismo Coppermix Single Plate S15 Clutch Kit

Nismo parts are high quality, properly documented, complete and install like OEM because they are, basically, OEM engineered. We reported in the first installment of Project 240SX about the Nismo Competition Parts clutch kit that we picked up from Tomei USA. The single plate Coppermix clutch is rated to hold 391 lb-ft of torque and engages lightly and easily. It’s also 1.4-lbs lighter than the factory SR20DET clutch. The Nismo Coppermix aluminum flywheel is 3.3-lbs lighter than stock for a reduction in rotating mass but the most important thing about our clutch kit is its S15 fitment.

The reason we went with a S15 clutch is because we also picked up from Tomei USA the holy grail of Nismo parts, the Silvia/180SX reinforced six-speed transmission. Many a S13 and S14 240SX parts swapper has 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 a S15 Silvia Spec R or one of the special six-speed Autech S15 Silvias. But that route has its own issues, as 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 Nismo Coppermix kit includes the clutch, pressure plate, flywheel, throw-out bearing, new flywheel bolts, and pressure plate bolts - everything you’ll need to install, except for the alignment tool

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

The Nismo clutch kit fit without any problems. Those familiar with the S13/S14 240SX clutch will now notice how much farther the S15 Silvia unit sticks out

Our old Exedy clutch kit showed obvious signs of abuse and overheating. Just take a look at the rainbow on the backside of the flywheel

Nismo Reinforced Six-Speed Transmission

The S15 Spec R picks up its speedometer signal electronically from the rear ABS sensor and a 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 speedo signal). So, unless you’re truly dedicated or don’t care to know how fast you’re going down the street, a S15 six-speed transmission is not a direct bolt in option into any USDM 240SX.

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 Tomei USA so we didn’t bother tearing the gearbox apart to cryo-treat or coat the gears. Tomei USA also sells the separate Nismo bolt-in kit, which includes the transmission mount, driveshaft, shifter, hardware and required harness extensions. The only other items you’ll need are a 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 drop-in into any S13, S14, or S15 equipped with a SR20DET or SR20DE engine. If you own a S13 or S14, you’ll need to swap over to a S15 clutch at the same time just like we did, on account of the difference in depth between transmission input shafts. The S15 flywheel, pressure plate and clutch will bolt on directly to any SR20DET engine.

The Nismo reinforced six-speed transmission kit from Tomei USA comes with the case pre-assembled and with Nismo labels for every single part. This includes the harnesses, bolts, transmission mount, shifter, and driveshaft

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 trannies don’t have this gear and require a lot more work to fit

Compared to the SR20DET five-speed transmission, the Nismo gearbox is 3.8-lbs lighter despite having one more gear inside

We paid a visit to Steve Rodgers at SR Motorcars in Gardena, California 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 and 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.

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 240SX 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 2nd, 3rd, and 4th gear have all been moved closer to each other, which helps us stay above the boost threshold when on track.

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

Nismo GT L.S.D. Pro

When it comes to 240SXs, a limited-slip differential is a must. Look at it this way - when Project 240SX 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 of it. The problem with this is that the non-spinning wheel, the one 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 play with the balance of the car using the throttle.

The Nismo GT L.S.D. Pro kit includes everything you’ll need for installation including new OEM differential bearings, pumpkin cover gasket and bolts. Be sure to get more synthetic 80W90 oil for the fluid change after break-in

The Nismo LSD even comes with new and 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

Twenty clutch plates are used within the Nismo differential to ensure that the locking behavior of the LSD is smooth and predictable. We went with a 1.5-way unit for track and street use

For Project 240SX, we wanted a LSD that was responsive and provided a smooth, easy breakaway at the limit. We again contacted Tomei USA, this time for a Nismo clutch-type LSD, and they told us about the GT L.S.D. Pro. Clutch-type LSDs work by using springs that apply an “initial torque” to the clutch plates found within the LSD 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 as they actually want their cars to kick out soon after applying the gas during cornering.

Unique on the market, the GT L.S.D. Pro features an externally adjustable initial torque setting. The standard Nismo GT L.S.D. makes use of 20 clutch plates to help smooth over the locking transition. The GT L.S.D. 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 LSD can be set trackside to compensate for power, tires or even the difference between a drift day and a track day.

We set our GT L.S.D. Pro to the Low setting in order to soften the rear breakaway characteristics for track use, which is highly recommended for all the non-drifters out there, on account of the S13 chassis’ notorious abundance of rear anti-squat geometry. SR Motorcars handled the Nismo unit install as well and it went without much trouble, although it was all too easy to be found playing with the external adjustment of the LSD. Chatter, clanking and noise-free, the GT L.S.D. Pro has proven to be quite the usable street LSD as well.

Hidden within the Nismo GT L.S.D. Pro is the 19mm head to adjust the initial torque setting. It’s possible to leave the LSD on the Low setting for street and road course use and then turn it to High for a drift day. Just jack up the car and pop off the right axle stub, no need to drain

New differential bearings are highly recommended when swapping out LSDs and here Steve of SR Motorcars prepares to press ours onto the differential. Be sure you have the right equipment before attempting this job

The simplest way to tell your final drive gear ratio is to count the teeth or check the ring gear. 49/12 = 4.083 for a R200V S13/S14 SR20DET manual. S13/S14 SR20DET automatics came with 3.916

We filled the pumpkin with the included 80W90 synthetic Nismo Versuspeed LSD oil and then broke in the differential by driving two hours to Buttonwillow Raceway and then doing laps. Nismo suggests a break-in of 186-miles at no more than 37mph. We’ve done, uh, more than that and at an angry pace that’s a bit faster as well. After another 550-miles on the car, we’ve only experienced the slightest of clunking when the car is cold and warming up. But once up to temperature, there is nothing from the LSD but glorious throttle steering. Faster and more fun? Works for us.

Continue on to Project 240SX - Part 3 - Track Suspension >>>

ENGINE
Engine oil cooler, AN fittings, SS line, billet remote oil filter mount, block adaptor
Earl’s Performance Plumbing
(310) 609-1602
www.holley.com/index.asp?division=Earls

Carbon fiber top air intake filter
K&N Engineering
(800) 858-3333
www.knfilters.com

DRIVETRAIN
Nismo Super Coppermix clutch, pressure plate, aluminum flywheel, reinforced six-speed transmission kit, GT L.S.D. Pro
Tomei USA
(949) 855-6577
www.tomei-usa.com

SUSPENSION
Mono Flex adjustable coilovers
TEIN
(562) 861-9161
www.tein.com

Urethane control arm, rear spindle, swaybar, endlink bushings
Energy Suspension
(949) 361-3935
www.energysuspension.com

Adjustable suspension arms
SPC Performance
www.spcperformance.com

INSTALLATION
Nismo clutch kit, transmission, GT L.S.D. Pro
SR Motorcars
(310) 516-1003
www.srmotorcars.com

Custom front tower, camber plate modification
M1 Fabrication & Development
(714) 671-0077
www.m1fd.com

Water pump, belts, electric fan relay
Mavrik Motorsports
(714) 523-1896
www.mavrikmotorsports.com

Urethane bushings, roll center kits, suspension
Tokyo Auto Repair
(714) 993-7300