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Here Katsu is buttoning up the R35 GT-R front differential. I would have taken a picture earlier, but I was working on some other part of the engine. OS Giken makes a Super Lock LSD for the front of the R35, but apparently the factory electronics do not agree with the front LSD. It has not been released to the general public for this reason. In the case of the ARK GT-R, we couldn't give a flying fuck about that because our car has none of those restrictive factory controls in the way. It was almost perfect because Mark at OS had a few in stock he couldn't sell to R35 owners and we took them off his hands. Of course Katsu WPC treated them as well. Remember, he works there part time which is very convenient for Team America!
Katsu built the R35 front differentials with custom made 4.11 ring and pinions made by the guys at Albins Off Road Gear just outside of Melbourne, Australia. The stock R35 front final drive ratio is 2.937:1 which is far too long to work with the Skyline GT-R's transfer case ratio of 1:1 since the BNR32's factory rear final drive ratio is 4.11:1. Albins had made these 4.11 front ring and pinions for another customer in the past which greatly reduced the lead time. Albins supplies the entire Australian V8 Supercar field and are also on multiple Baja 1000 winning cars.
Optionally available from Albins is also this shim kit for setting the ring and pinion backlash. This is necessary to make up for manufacturing tolerances. At these kinds of high power levels, everything must be built perfectly.
I had an extra transfer case in my small collection of Skyline GT-R parts so Katsu took one apart and rebuilt it. The center differential is located inside and this is where the AWD magic happens. It was the original unit that XS ran in the car when it was running the stock 5 speed transmission so Koji had already rebuilt it with new and extra clutch plates back in 2004. It only had a couple of Time Attack events on it so it was still in excellent condition. I think up to two extra friction plates can be installed to engage the front wheels more aggressively. The WPC treatment once again smoothes this engagement which would otherwise be a bit abrupt with the extra clutches and plates. A lot of the Skyline drag racers in Japan use this trick to ensure 50/50 AWD 1400 horsepower launches. The center differential engagement can also be controlled to some degree with the center diff computer piggybacks. In the case of this car, we will not need any piggybacks as the Pectel ECU SQ6 will be controlling the center differential.
The factory Nissan transfer case, after being rebuilt by Katsu, conveniently bolts directly on to the rear of the Holinger sequential transmission. Holinger has made a GT-R specific box for many years now and they are still used in many of the most powerful Skyline GT-Rs around the world. The unique thing about the GT-R gearset is that it uses helical gears which makes the box surprisingly quiet. While the Holinger costs a pretty penny, it's woth the peace of mind to know the box is well proven and highly developed. Small, motorsport grade details such as deburred castings, drilled and lock wired fasteners and REM treated gears all make this box top notch.
While we're on the Holinger, here's the front view showing the optional clutch release bearing. Mounting the release bearing like this eliminates the sloppy forks, spring, and mediocre factory grade bearings. Right above the Holinger release bearing assembly is a gear position sensor. Gear based ECU strategies such as boost control, active aero control, and others are possible. With a GPS unit, and some maths, the Pi Electronics Sigma Elite logger could theoretically allow extensive active aero control in conjunction with gear, wheel speeds, shock position, lat/long G, or any other inputs. Admittedly, aero is the weak point of this car right now, but I hope to get together with an aerodynamicist in the near future. Also, half of the VQ35HR engine to RB26 transmission adapter that Tyler designed can be seen here.
