andrewhake

After driving my car with a similar rear end setup, I definitely agree. I initially found myself trying to predict and react to the car and how I thought it would behave with the torsen diff. The ability to recover traction on exit is extremely predictable, and the confidence to get back to full throttle that much earlier really makes a difference. The behavior of the car on turn in is also really stable and predictable now. Very easy to brake deep into a lowspeed corner with full confidence knowing the car will rotate.

odb812

Thanks for bumping this thread up, guys. I've been meaning to write a quick update.

I've done a lot of autocross and a handful of track days since my last update and I'm still very happy with the OSG. The confidence the diff gives me has been instrumental in my improvement as a driver. I've noticed that before I had the diff I would pretty much do the same thing on corner entry from run to run and try to find all my time on corner exit and changing up my line. With the diff I feel like I can chuck the car in, so I've been focusing a lot more on entry speed and my brake release.

Another huge bonus from the diff is my consistency in times. When I do make mistakes I'm able to reel the car back in without slowing and I'm much less likely to spin. With the diff masking these mistakes I get times that are more reflective of what I was trying to improve on that particular run--there's less variance in the time from mistakes that I have to account for when I'm analyzing if the thing I was trying on that run was better or worse. In the past I'd be less likely to try new things run to run because I'd always feel like my execution of what I wanted to do that run wasn't 100%, so I'd spend my next run trying to clean up mistakes.

Glad I'm not the only one who had to make that adjustment. I've been driving my IS300 with an open diff a bit more at autocross and on track as well as hopping in friends' cars and at first it was a big adjustment going back and forth from car to car. In the s2000 I'd correct with way too much steering angle and in the IS I'd use way too little. After a while of going back and forth I started being able to catch mistakes in the IS earlier so I'm starting to correct in both cars with very little steering angle. I feel like the clutch type makes some of the driving fundamentals that are not specific to the diff easier to learn and I can take those improvements with me from car to car.

DavidNJ

Question to those using the OS Giken: Have you ever had a tuning adjustment made?

For the 1.5 diff there are 4 different ramps, 3 different pressure plate spring rates that can be combined into probably 9 different settings in addition to reducing the number of active clutch disks. The adjustments change how quickly and how much the diff locks up. I was told the diff ships with a combination OS Giken considers correct for an NA S2000.

Thanks,

David

odb812

I was working with SpeedFreaksUSA and OS Giken about providing custom specs and they were both open to making that happen, but what they told us about their OTS setup was pretty much what we were looking for anyway. From what I know it seems like OSG has a bit of R&D in the S2000.

DavidNJ

The tuning thing appears complicated.

This article talks about tuning a Salisbury rear starting on page 5 through page 7: http://www.taylor-race.com/pdf/under...ferentials.pdf

This one, Differential Behavior, has some interesting concepts but I haven't quite figured out its practical application: http://www.optimumg.com/docs/Differe...ertaReport.pdf

This video is really trying to sell a product, and he never gives enough info to be useful, but he talks about differential tuning in terms of in corner behavior and laptimes:

odb812

This is long overdue, but things have been pretty hectic for me since the Crow's Landing ProSolo and NT.

ProSolo:

This year I only drove my car about 5 times or so before the ProSolo. Each time we had something drastically different about it. At the end of last year we changed up the rear sway bar and found the car likes more bar and less spring. We went through a few iterations of changing springs, front and rear sway bars, and alignment and arrived at a pretty common setup for STR with the Karcepts front bar.

I was on the fence about running my RE71Rs from the tour and pro last year but ended up going with the Rival S 1.5 like most of the other STR drivers. We had been planning on testing the Rival S, but still wanted to get the balance dialed in with all the spring and sway bar changes first so we're not chasing moving targets. The 5 runs we got on the practice course before the pro ended up being the only time we got on the Rival S 1.5 before the regionals.

During the Pro I was struggling a lot. On the left side there was a big seam in the concrete right where you stage. I couldn't figure out if I was rolling out of staging or if there was an issue with the timing system--the system wasn't giving the same feedback with the lights that it usually does when you roll back or roll over. There were a bunch of others experiencing the same thing Saturday morning and they gave out a bunch of reruns because of it. On the right side I was dirty all day Saturday, but I played it really conservative Sunday to get a clean run in. Fortunately I was only a few tenths off of my fastest dirty time on the right.

I also struggled to get used to what you can get away with on the Rival S tires. Between the fact that the car was way more stable than it had been so far that year and how much more slip the Rivals can hold, I was driving way below the limit. I ended up towards the back of a very competitive pack.

My co-driver, Praneil, adapted to the tires and the new setup much quicker than I did, but seemed to be still figuring things out even on his last runs. He ended up taking the 6th spot.

National Tour:

For Crows Landing this year the National Tour followed the Prosolo. Even though we(especially I) could have used the seat time, neither of us could get out of work Friday to go test. We started off Saturday with the same setup we used for the Prosolo.

STR was running in the first group on a very windy Saturday morning, cleaning the course for everyone else. It was hard to keep any heat in the tires with the wind and no tire covers(we tried using floor mats with not much success). The course started with a sharp right into a slalom. The first run I got a bit sideways in the slalom on the cold tires so that was a throwaway. Basically you had to be very careful in that first slalom and just trust that the car had more grip for all of the elements after that. On my second run I was a bit too trustworthy of how much grip the car had and spun it in a high-speed sweeper. I was sitting pretty close to the bottom with one run to go. Rather than playing it safe and getting a clean run in the books I decided to go for it on my last run and spun it pretty close to the same spot.

At the end of the first day Praneil was less than a tenth behind Yom in his S2000 but they were both a second behind Bauer in the ND.

Sunday wasn't as windy, but I was still concerned with how much I struggled to feel the tires out on Saturday. I ended up cruising the course on my first run, adding a little pace the second run, and going for a quick, smooth run for my third. My third run was respectable but still a bit slower than the Sunday time of the last trophy recipient.

My co-driver was .2s behind Yom after his second run on Sunday, just over .3s for the weekend. Yom coned his last run, but Praneil got a little loose going through one of the boxes on his last run and didn't find any time. Bauer in the ND was still a bit faster than the S2000s on Sunday, so he finished with over a 1 second lead on the rest of STR.

Takeaways:

This year I felt more involved in the tuning process. The big changes were all still coming from Praneil but it was more like a conversation this time around. I feel like if I had shown up for testing the Friday before the Prosolo by myself I would have still made the same setup changes with the same results as I did with Praneil's help.

With the consistency I get with the diff I can get meaningful feedback in both the feel and the times with a single run. That was a game changer this year since we were making so many changes in the car's setup so close to regionals.

I still believe that a clutch-type diff that is set up well is more important for getting you to the pointy end of the field than it is for people already at the pointy end of the field.

jst2878

andrewhake

It is 80w-250 fluid from OS Giken. And yes I have run it exclusively with my 1.5 way. I was recommended by the people that built my diff to give it some time to run-in (1000 miles or so) and change the fluid, and after that it should be good to go for a very long time, even longer than the regular OEM interval. The fluid removed on that initial fluid change had a decent amount of buildup on the magnetic plug as expected. The fluid is definitely a bit shocking with how thick it is, but it is what OS Giken recommends and seems to work very well and keep the LSD very very quiet. I think I have put over 10,000 miles on mine now and never even hear a thing from it. Initially I heard some small noises when repeatedly reversing and moving forward but I don't even get that anymore.

Overhual really depends on use case. I legitimately think you could do normal day to day driving for 150,000+ miles after doing the initial fluid change without issue. The fluid lasts a very long time. Without dedicated track driving every weekend it is more likely you will end up changing the fluid because it is old rather than it being worn out. I believe most somewhat regular track day drivers change the fluid once per season/year. Which is what I am planning.

andrewhake

Something else I think is worth adding to this thread is how drastically this diff has changed the way the car behaves when driving in the rain. The amount of additional grip and feel I have compared to the OEM diff is substantial to say the least. You have to be noticeably more aggressive to get the rear end to step out in the wet. It does it's job very well all the time, but it is extremely noticeable in the rain for me personally.

I personally wouldn't (ever) recommend using stiffer front spring rates than in the rear on an S2000, but even more so when using a 1.5 or 2 way LSD. The increase in turn-in and corner exit traction make the car quite a different animal. With everything nicely balanced, I can get back to full throttle quite violently and the car remains incredibly well composed with very mild steering inputs.

InsaneSp

I really need to build my spare diff with 4.44's and a OS Giken.