mx5-kiwi

Given we (I, me, Royal "we") are now moving towards a gearbox (thanks K-Miata) that will handle significantly more power and I presume many of us will slowly be upping power levels.

It has me thinking, have "we" gotten any closer to knowing the failure point of the OEM torsen diff yet?

I imagine we will be heading (with zero failures or issues HAHA) towards 400 hp atw or more over the next year or so.....

and while I lust for an OS Giken, to date we have had zero issues with the OEM torsen running 250 - 320 HP atw with a 3.9 and 4.1 ratio.....in a circuit racing environment.

So figure we may as well stick with it, unless it's known the failure point is imminent.

flier129

iTrader: (7)

If your classing allows for after-market diffs and you are still using OEM, you're missing out. Especially if you're fighting for tenths! The few cars I've driven with an OSG were noticeably more stable on entry, which allowed me to concentrate on entry rotation. There's other advantages to a high-quality clutch-type diff as well... ramp angle, more consistent locking, others I'm missing.

In regards to failure points on the OEM torsen, I know mine is worn the hell out. The thurst washers can wear out and it functions like an open-diff sometimes. There's rebuild kits as well: https://supermiata.com/miata-diff-bearing-seal-kit.aspx . I don't think this wear is attributed to big power, though.

This video is also interesting:

DeerHunter

I successfully ran an OEM Torsen with my big-turbo stroker for several years. It was only when at a drag strip - traction compound coupled with wheel hop - that the worm gears disintegrated. Under normal use, wheelspin is the natural outcome and that provides a great "fuse" for the driveline.

I now run a billet Guru torque-sensing diff that I don't expect to ever see a torque-related failure. Sadly, they're NLA.

mx5-kiwi

Thanks for advice so far.

I wonder if you wouldn't mind adding power level and tyre type, tyre width, track / road, drag strip etc. as I imagine it's relevant.

I possibly should have also posted this in the race prep section but I seem to only ever post there and thought I should expand my horizons

DeerHunter

Summer High-performance tires (195 or 205/50R15) on the street = no problem
Nitto NT-01 or Toyo RA-1 (205/50R15 and 225/45R15) on high-speed autocross course (abandoned runway) or track (dedicated road course) = no problem
Street tires on drag strip = kaboom!

Power is approx. 350 to the wheels and somewhere north of 300 lb-ft wheel torque.

themonkeyman

mx5-kiwi

Good question.

The main reason is in 3 years I only ever once felt the drive move away from both wheels and that was me being very aggressive on a rumble strip. Other than that I have never felt an issue with drive in regards 1 wheel versus 2 doing the work. Both my 3.9 and 4.1 have always felt like they are working properly. Stability under brakes is very good. For good or bad, we still don't run a bias adjuster.

But as we increase from 300 - 320 HP atw and 290/300 ft/lbs upwards I suspect this "might" become an issue.

Secondly, the availability of the GM diffs you guys have access to is just not available to us. We (more or less) don't get any of those vehicles here.

Thirdly cost, the kit alone with freight, duty and exchange rates works out to be about 3-4 times the cost it is for you guys in the States.

IF we are to ever do anything it would most likely be the OS Giken, the single unit significantly minimizing freight, isntallation etc.

BUT I still have to appreciate how or why we don't "seem" to be having any drive related issues. I don't "think" I am that ham fisted, that I am not noticing....