The COBB Tuning Motorsports team and I just got back from our first weekend of testing at California Speedway with the new OS Giken TCD rear Limited Slip Differential (LSD) upgrade for our GT-R. With nearly 800HP available at the wheels, I had been experiencing significant rear wheel spin on corner exit that was obviously hurting the car’s ability to put power down coming out of the turns and hurting our lap times.

During the install the OS Giken LSD looked quite a bit beefier than the stock part it was replacing. Probably because it has a grand total of 28 friction plates inside! These plates can be configured to provide progressive locking up to 100% and with that many plates there are quite a lot of tuning options for us to fine tune the amount of lock-up we want.

My first impression was “WOW!” What a difference the TCD LSD made! As I started my first hot laps I could feel the difference in the rear of the car. Now the chassis just seemed to hunch down in the back and squirt out of the corners with no rear inside wheel spin at all. Plus it was much easier to use the throttle to help steer the car out of the corners. With the inside wheel spin gone, I could easily modulate rear slip angle with my right foot, encouraging corner exit rotation by feeding in just a bit more throttle.

As they say, the proof is in the data, and we have data. In this first screen shot is data from last year with the stock rear differential. Focus on the section where throttle position begins to increase and look at the difference in rear wheel speeds.  At some points there is as much as a 14 mph difference between the rear wheels. And this was on super sticky Hoosier R100 slick racing tires!

This next screen shot is from data recorded during our test day with the OS Giken TCD LSD installed. Looking at the wheel speeds you can see they are much closer together and how much the rear differential is working.  It allows a small amount of slip under deceleration, and locks up 100% under acceleration.  In fact you can see that for most of the graph the left and right rear wheel speeds are so close they are indistinguishable from each other. What makes this even more impressive is that we were running on Toyo RA1 DOT racing tires. DOT race tires are not nearly as sticky as the pure racing slicks we used last year, so it is clear to see how effective the OS Giken rear diff is, even with much less traction from the tires.

The data also revealed that we still are suffering from front wheel spin. The OS Giken rear LSD is working so well we may need to encourage them to release their forthcoming front LSD as soon as possible!

We’re in the final stages of preparation for Round 1 of the Redline Time Attack Series which kicks off this weekend, March 27 & 28, at Buttonwillow Raceway in Buttonwillow, CA. If you are in the SF Bay or LA area, come on by to say hello and stick around to see how our monstrous Nissan GT-R fares as we take on the hotly contested Modified Class.

Brian Lock
COBB Tuning Motorsports