Now that we’ve shown you how to improve the all-motor power output, handling and braking of your Infiniti G35 or Nissan 350Z, it’s time to discuss one last but surprisingly effective upgrade: the limited slip differential.
With my ’06 G35 coupe turning lap times in the 1:23’s around Toronto Motorsports Park on 240 UTQG Goodyear summer tire, the OE viscous limited slip differential was starting to show its age and limitations. The viscous fluid that gives a V-LSD its torque-transferring ability breaks down over time, a process that’s accelerated from the severe heat cycles that come with track duty. Plus a viscous diff by nature is not very aggressive in its lockup characteristics and tends to overheats after a few laps, losing much of its ability to transfer torque to the rear tire with the most grip, so I was pretty sure a clutch-type LSD would result in a meaningful drop in lap time.
To test this theory, I contacted my friend Yasu at Performance Partners Inc. PPi is an authorized U.S. dealer for ATS (Active Traction Service), a highly reputable Japanese manufacturer of clutch-type limited slip differentials, clutches, final drives and transmission gear sets. Because my G was my daily driver, I’ll admit I was a bit wary of using a clutch-type LSD since these tend to be quite noisy, especially when making slow, tight turns. The chattering noise and lockup hopping across the rear axle isn’t an issue for a race car pulling out of its pit box, but for a street machine it can be more than a little embarrassing pulling into a parking spot with the rear end of the car chattering and juddering around.
To address the noise and smoothness issues of a clutch-type differential, ATS has developed what they call the Super Silent LSD. This is still a metal clutch-type differential and therefore retains the aggressive lockup and torque transferring that comes with it, but by reducing the cam angle and redesigning the clutch pack for a quieter, smoother and more gradual engagement. ATS claims the Super Silent LSD is as quiet as a viscous LSD or gear-type (Torsen or helical) LSD if you opt for their 45-degree cam and 12 clutch plate setup, though this is also the mildest setup with respect to lockup characteristics. For more aggressive lockup you can go to 16 clutch plates and for even more you can move up to 60-degrees of cam angle. Check out the chart above to see how customizable this LSD really is. I opted for the 16 clutch plate setup with 45-degree cam angle, so a bit more aggressive than the mildest setup but still quiet enough for street use, or so I hoped.
To make the installation a little easier, I picked up a used pumpkin from a wrecker so that Andrew (from Auto Analyser Racing and Mantella Autosport) and I could build it with the Super Silent LSD while I drove around on the stock diff until we were ready to swap in the freshly built unit. For starters, we drained the diff fluid and removed the cover from the spare diff and then Andrew measured total preload, ring gear to drive pinion backlash and ring gear runout.
After that Andrew carefully marked all the fasteners, bearing caps, and shims so we could put each back in its original position and then we pressed the roller bearings off the factory diff and onto the ATS diff. Then we transferred the ring gear over and torqued it to spec using a fancy schmancy digital OTC Angle Meter. One of the many reasons we love working with Andrew is he always does things properly, using the best tool for the job and following the factory specifications. We learn something new every time we wrench with him and it’s amazing the skills and knowledge stored away in this dude’s engineering-supercomputer brain.