NX GTi-R The Search For Traction – Part Two

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I was on vacation in B.C. last August when Paul texted me with a problem. The Nismo diff didn't fit! I saw dollar signs everywhere – then Paul said that the B15 diff had the exact same tooth count and, obviously, was the correct diameter. It was simply a matter of swapping the two of them. The crown gear on the Nismo LSD was slightly larger. I hadn't read about that before, but here we were.

The task was hopefully simple enough. Tear down the B15 transmission, remove the factory LSD, insert the Nismo LSD, and put it back together. As the B15 transmission was used, for safety sake I gave Paul the go ahead to replace any parts that showed signs of wear. Then I had to walk away, not only because Paul does not like the distraction of someone peering over his shoulder, but because I was heading to British Columbia with my wife to visit my daughter and her husband (This all happened last August). We had an awesome vacation and one of the highlights was a day on a beautiful sailboat with Sunshine Kayaking on the Sunshine Coast – home of the Beachcombers. You have to be Canadian and have a few gray hairs to understand that reference. If I ever give up racing, then I want to get into sailing on the Pacific! Captain Greg let me take the helm and it was an incredible rush!

Captain Greg from Sunshine Kayaking talked me around the open water the way that I would talk someone around a race track. What a beautiful way to spend an August afternoon.

The Sentra B15 transmission was in good shape when Paul pulled it apart. 

Shortly after getting off of the sailboat, I got a text from Paul indicating that he had a problem with the installation. While I thought, based upon my huge knowledge of transmissions and differentials gleaned from the Internet, that the Nismo LSD was a drop in replacement, Paul had discovered that it was not. The crown gear on the Nismo LSD had the right tooth count but had a just slightly larger outside diameter. This meant that it did not fit properly. This is where I am glad that Paul was working on this for me, because I may have tried to make it fit! Without any hesitation, Paul removed the crown gear from the factory B15 LSD and installed it onto the Nismo LSD. Presto! Everything works. Even better, the dollar signs that had started flashing through my brain when I heard “problem” were quickly vanquished and the transmission was ready to go in the car.

Unfortunately, I am in the situation where I am not working properly. Last summer I was facing some health issues that I am overcoming but, seven months later, they are still slowing me down. I share this to break the news that I have not installed the transmission in the NX yet – I just do not have the strength to bench press a transmission into place. That and my good buddy and engine builder, Dave Schlueter, has turned his mechanic's garage into a woodworking shop while renovating his kitchen. I hope to see the transmission install happening soon. When it does, I will convert the B15 transmission back to a B13 style cable operated clutch. The cable clutch works well for me with my Infiniti G20 setup and I have lots of spare parts.

Paul not only rebuilt the internals, but he cleaned and painted the housing also. Talk about a difference!

In Part One I discussed that the Sentra B15 transmission had better gear ratios for my needs than my current transmission, which was from a 1999 Infiniti G20. Here's why (thanks to all of the guys on the SR20-forum who contributed this information):

On a road race course first gear is rarely a factor, and at best even with the longer gearing of the G20 transmission the turbo engine blows through first gear. With the B15 transmission second and third gear should be much more aggressive, with fourth and fifth gear slightly so. My mathematics in the above chart is all theoretical but I think will help demonstrate the advantage of the B15 transmission. I hope to find that advantage on track come spring. Will the consistent 205 KPH (127 MPH) be moved to the 215 KPH (133 MPH) range at Canadian Tire Motorsports Park's long uphill 'Andretti Straight'? I hope so. The final drive ratio should provide much better pull on the long, uphill straight and the Nismo LSD should provide incredible traction through Moss Corner, allowing me to have significantly better exit speed. In the past all I have done is burn off rubber on the inside front tire. Better exit speed equals a better top speed coming into the next corner. And that is what I am looking for.