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Old 06-05-2013, 06:07 PM   #21
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Never had a problem with an OS-Giken causing push myself. The OS-Giken is similar to a Torsen in that the lockup is smooth and progressive as you add torque. Even on torque it allows for some differential wheel speed while cornering for optimum traction. Unlike the Torsen however there are more things to fiddle with and I don’t think the optimum setting is the same for all application cases. You can seem to dial in not enough initial lockup and still get too much inside wheel spin or too much and get some mid corner push. It seems to me quick transitions from on throttle to off throttle in second gear like in autocross want a little quicker lockup than what feels wonderful on the track assuming the same suspension setup. It seems however I got good balanced setting by just removing the rear swaybar when I autocross.
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Old 06-05-2013, 06:28 PM   #22
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Never had a problem with an OS-Giken causing push myself. The OS-Giken is similar to a Torsen in that the lockup is smooth and progressive as you add torque. Even on torque it allows for some differential wheel speed while cornering for optimum traction. Unlike the Torsen however there are more things to fiddle with and I donít think the optimum setting is the same for all application cases. You can seem to dial in not enough initial lockup and still get too much inside wheel spin or too much and get some mid corner push. It seems to me quick transitions from on throttle to off throttle in second gear like in autocross want a little quicker lockup than what feels wonderful on the track assuming the same suspension setup. It seems however I got good balanced setting by just removing the rear swaybar when I autocross.
Hmm, it sounds like your giken isnt setup like it comes from giken. Or maybe old giken was different. Recent the recent giken I've been dealing with came from them set at 100% lockup, IE when the diff locks it becomes a spool, according to giken they have a patent for this and they're the only ones who can achieve full lockup in a clutch type. I'm guessing yours has 1 pair of clutches deactivated so its at 80% lock, which might work for a high HP car.
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Old 06-05-2013, 06:36 PM   #23
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Hmm, it sounds like your giken isnt setup like it comes from giken. Or maybe old giken was different. Recent the recent giken I've been dealing with came from them set at 100% lockup, IE when the diff locks it becomes a spool, according to giken they have a patent for this and they're the only ones who can achieve full lockup in a clutch type. I'm guessing yours has 1 pair of clutches deactivated so its at 80% lock, which might work for a high HP car.
Mine is the High HP setup some of the center bits are slightly different. It locks but not as quick at low torque levels in transition as the standard setup. powering over FIA curbing however it keeps putting torque down like it is locked unlike a Torsen however.

Last edited by bbundy; 06-05-2013 at 06:50 PM.
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Old 06-05-2013, 08:08 PM   #24
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Out of the box, the OS Giken I purchased from 949 did not fit my driving style at all. The springs were too soft which caused a digital on/off lock feeling. A lift at corner entry would bring about too much rotation - the back end would step out. I suppose if you like to slide a car, that is fine, but my driving style is smooth. I know plenty of racers that like to grab a car by the scruff of the neck and man-handle it around the corner. That is not me. Power-on car to push at exit. So while my car was balanced with the V2 4.3 torsen I previously ran, the OSG was loose on entry and tight on exit. This car is race/track-only. Stripped and caged. 225 Hoosiers. 186hp at the wheels. Driving in the rain was 'interesting'.

A friend with a track/race-only MX5 had a similar experience with his stock out-of-the-box OSG. I thought he was exaggerating the problem until I drove his car and almost put it into the wall - it was terrible. I purchased my diff at the end of 2010, I believe. He bought his in 2011. We both got to installing them a few months and events apart, in 2011.

We both changed swaybars and settings, and shock settings. I think he even changed springs. Eventually, he sold his OSG, went back to the stock Torsen, and started setting lap records again.

After trying several different setup changes, and more different fluid combinations than I care to remember, I boxed up the OSG and went back to the Torsen. I spoke to a few people about the OSG, including the tuner that builds the OSG diffs for Turner Motorsports (he is 2 towns over from where I am). His comment was that none of the OSGs he has seen has been good to go out of the box for anything but street-driven cars. I Eventually spoke with Ben Herne of Puddy Mod Racing, known and respected for S2000 and OSG diff builds and not a stranger to Miatas. Ben had other customers with similar experiences to mine, and had some tuning suggestions. Since I wanted to try a different final drive ratio, I decided to give the OSG another try.

I sent my diff to Ben, who changed out the springs and did some other magic. He assembled and setup the diff in the housing with a different ring and pinion (4.56:1). The price was great and the service even better. Ben also provided me with some suggestions for proper diff fluid which proved to be invaluable. If I recall correctly, he laughed out loud when I mentioned that I had read online that these diffs do not need to be broken in.

Ben's magic was well worth the price, and in my experience, is the way the diff should have been setup and supported from the factory. I had previously called OSG a few times, and each time, felt like I was speaking to someone behind a parts counter. My experience was that OSG customer service is nothing more than a parts department. I gave them specific information on how the car was handling, and their response was 'well, it shouldn't do that'. I asked how the diff was set at the factory, and couldn't get an answer to that either (which spring rates and how many, how many clutch plates in total and how many activated, which shims, etc).

After all is said and done, YES, I can get on the power a bit sooner at corner-exit with the OSG than with the Torsen. However, it was my experience that buying an OSG is like buying any other adjustable suspension part; you have to adjust it to your needs. In my case, that meant that I should have budgeted for someone to do it, which I had not. Tuning the diff requires dropping it, draining the fluid, taking it apart, and re-assembling. In my experience, this is something a shade-tree mechanic will want to have a professional do. So you have to budget for it. In my case, it also required shipping as I live in New England and Ben Herne of Puddy Mod Racing is in Florida. Between tuning, shipping, and removing and installing the diff several times, the additional cost was not cheap.

Given the cost and complexity versus the payoff, this is one of those mods that I would put at the bottom of most people's list, if at all. The stock Torsens are very good and affordable, for what they are.

This is likely not a popular stance to take in the Miata world, but it is my experience and the experience of another trusted friend and racer.

- Will
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Old 06-05-2013, 08:23 PM   #25
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I'm glad I saw this. I had been considering giving one of these a go, but I've been using the Torsen II from a 99 with a 3.9 ratio, and I think unless something breaks I will probably stick with it.
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Old 06-05-2013, 08:27 PM   #26
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Thanks for your input Wildo.

Right now I have a welded diff, which is working out ok I guess. Hoping to build up my spare properly one day.
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Old 06-05-2013, 08:30 PM   #27
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Out-of-the-box OS Giken. I don't see oversteer on entry or a mid-corner or exit push...

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Old 06-05-2013, 09:23 PM   #28
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My experance is only with fiddling with setting up the High HP setup. This was something Emillio at 949 worked out with engineers at OS-Gigen to try to reduce the level of instant lockup sensation seen when you put the thing in a car with 2 or 3 times the stock torque level on sticky tires. I adjusted and tried it with 3 different adjustments and became really happy with it the way I have it now. I dropped time on the track but I sadly don’t have good direct A to B to compare how much time it was worth.

I will say that for a car with 350 rear wheel hp that on the track I think the diff is certainly helping me look like a better driver more so than the torsen. Efficient power transfer coming out of corners means higher speed for the greatest percentage of the distance on a track possible.
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Old 06-05-2013, 09:26 PM   #29
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Originally Posted by Leafy View Post
I never said it understeers on entry. The issue is understeer mid corner and exit when you try to power out and the diff locks. 100% lock is too much, 80% lock is too much, 60% lock is not enough. There needs to be a 70% lock option but that isnt possible without a redesign of the diff that uses more clutches. I can say that because I've physically pulled a Giken apart and flipped around the clutch plates to change it.

The OSG cant move any torque, it is a clutch type. The max TBR on a clutch type is 1, which is lower than the TBR of either of our torsen options. The most torque it can apply to the outside tire is 50% of the total torque, and that would be at 100% lockup.
There are other ways tune an OSG to reduce lockup.

Deactivate plates which is what it sounds like you have done.
Change fore/aft ramp angles
Change pressure ring springs
Change cone washer preload and spring rate
Switch some plates to TCD's

We have at least two fast autcrossers on our hi-power tune that are quite happy. We encountered similar issues with our Rotrex boosted NB1 a few years ago. That started us experimenting with tunes and resulted in the current hi-power tune. We are now working with OSG to revise the standard out of the box tune for next year and further tweaking out hi-power spec.

So yaah, if the OSG didn't work out of the box for you, tune it. Included in the price of the diff from us is tuning support.
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Old 06-05-2013, 09:30 PM   #30
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How exactly does one change the ramp angles? A die grinder, doesnt feel like the correct tool for the job. Already played with the springs I believe it has the springs labeled 1.8 in it right now. There is a 1.6 set sitting on the shelf, and IRRC the 1.4 spring was making it act like an open with the clutches set to 100% lock.

Last edited by Leafy; 06-05-2013 at 11:46 PM.
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Old 06-05-2013, 09:31 PM   #31
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How exactly does one change the ramp angles? A die grinder, doesnt feel like the correct tool for the job. Already played with the springs I believe it has the springs labeled 14 in it right now. There is a 14D set sitting on the shelf.
Contact Ben Herne or OSG for info on changing ramp angles.
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Old 06-05-2013, 10:02 PM   #32
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Ramp angles are what changes how quickly it locks as torque is applied. I don't fully understand how it differs from changing springs. Seems like one of those black art things where the physics is more complicated than simple engineering static force calculations can explain well.
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Old 06-06-2013, 12:17 AM   #33
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Wow, this thread got real interesting fast.

Emilio, my purchase would be from you if I do decide to go this way. My car has around 240hp at the wheels but will be around 260-270 in proper tune and boost.

I too tend to be a pretty smooth driver. Our tracks tend to be not as wide open as yours many 2nd and 3rd gear corners. Do you see ny problems with out of the box setup for me....NZ is a LONG way away and finding an OS Giken tuner here is not entirely likely (well experienced anyway).....
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Old 06-06-2013, 12:35 AM   #34
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Is it possible that Leafy and jmann's buddies are talking autocross-specific experience and Savington is speaking to road course work? I imagine "mid 'corner'" in a parking lot/on an airstrip is significantly different than on a circuit.
Andrew has driven my OSG equiped DP car at an AutoX or two. I'd say we are both fans of OSG diffs on AutoX cars too.
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Old 06-06-2013, 01:01 AM   #35
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I am not sure what was done to my OSG but it's pure magic on the track. I am amazed how soon I can get back to throttle compared to others. Far from a light switch. Very progressive.

Once sorted you will be thrilled. I can't imagine any diff being optimized across a wide enough range to cover autocross and open track.

Last edited by k24madness; 06-06-2013 at 01:47 AM.
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Old 06-06-2013, 04:23 PM   #36
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Originally Posted by mx5-kiwi View Post
Wow, this thread got real interesting fast.

Emilio, my purchase would be from you if I do decide to go this way. My car has around 240hp at the wheels but will be around 260-270 in proper tune and boost.

I too tend to be a pretty smooth driver. Our tracks tend to be not as wide open as yours many 2nd and 3rd gear corners. Do you see ny problems with out of the box setup for me....NZ is a LONG way away and finding an OS Giken tuner here is not entirely likely (well experienced anyway).....
Just order our Hi-Power tune.
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Old 06-07-2013, 12:54 PM   #37
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Originally Posted by wildo View Post
- Will
FWIW I bought my (unused) diff second hand and it was built by puddymod with their full package. solid input shaft bearing iirc, cryo, 3.6...etc.etc

he may have tuned it but I never contacted him about what was done to it... I just know IT WORKED.
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