I just have mine done with every oil change

After this weekend's track day, I gotta say, it's not biting fast enough. I have to get my retuned for more aggressive use. And....just knowing that means dropping the diff AGAIN.... :shakes head:

Fortunately, for me, OS Giken is about 10 minutes away from me ;)

Getting my retuned diff back today. Looking forward to testing it.

Just reading through some diff threads for other platforms

BMW M3 crowd has a guy that is a diff expert, tests off the shelf and builds custom setups.

consensus from track crowd was that OS Giken did not lock hard enough out the box and needed to be upgraded to more aggressive specs

interesting because I had not heard that from z34 track guys - who, to be fair, may not be putting out the same power

Mine needs redone.

I went that route. Tuned by OS Giken themselves.

so it really is a bit too "soft" out of the box?

According to the OS Giken techs when I sent mine in for tuning. It's tuned for stock power and aggressive street driving

Yeah, I sent them my dyno graph and all associated info for my setup, so I expect the new "tune" to be much, much better.

I'm actually surprised by their soft initial setting. Most of their other OTS setups for many other car makes are great for track use. Oh well, live and learn.

I keep up with the E92 M3 crowd, and general consensus for the most part is the Giken OTS setup is great for track use. Some of that is because almost all owners don't really spend alot of resources to make much more power over stock, they focus on handling. Also, that car is tire limited really due to the body design. The exact opposite is true for the Z, most owners try to make considerably more power over stock, and the car can easily be over-"tired" due to the big body design. For the tire we can stuff under this car, it really needs to be making like 375 whp+. Not feasible for us NA track guys, unless you want to build a crazy 3.8L like the GT4 cars in Europe ran!

I've got a spare diff pumpkin just waiting to be rebuilt with a Giken for my M3, but just haven't gotten around to it. Knowing this though, I will certainly check into it before pulling the trigger for that car.

Being a Z34 owner with an OS Giken that I track often, and I think it's not biting hard enough....I think it has also to do with the fact that I've got a 4.08 FD, meaning the car is behaving as if it has a bit more power than stock.
That being said, the diff works well, it only locks up slower than I'd like if we're talking about a very sharp hairpin corner and I wanna drive through it like a maniac.

I had a call with a diff specialist from the Netherlands where I bought the OS Giken unit, and they said it's not a problem to tune it to bite earlier at all. You just need to swap out the negative preload springs for softer ones and that's it.....but to do that, you need to disassemble EVERYTHING.

Got my rebuilt Giken installed and tested, and it's a world of difference. Lock up is much harder, and no inside wheel spin. Car handless better than ever.

@ Prandelia - so what exactly did you do regarding the tune? How did you tune your diff?

I currently have my diff out and yesterday I went ahead and opened the OSG unit. My plan was to release some of the negative preload springs which would result in quicker lockup.
Stock I have 4 sets of 3 springs, each 28kg - one on either side. That totals 336kg of negative preload. I removed 1 from each side and I also exchanged 1 for a softer one, giving me just 184kg of negative preload. I'm now questioning whether I overdid it? I still didn't mount the differential back, so I'd like someone more experienced to chime in and give me their thoughts.
I am thinking about keeping stock springs, but just removing one per quarter, which would result in 224kg of negative preload, which might be ideal - but I'm not sure. I don't want it to behave exactly like a welded diff...but I do want quicker lockup.

Thoughts? Thanks!

I'll have to look it up. I just let the wizards at OSG tune it for me. I let them know I didn't necessarily want it to lock up much faster, but harder. It's progressive which is nice, didn't want to lose that, just need more overall lockup, but I'm sure it does so a little faster.