Rear Diff Options - Power Oversteer Found Here
 

***STICKY PER CHAOTICHOAX - DO NOT UNSTICK***

updated 2/7/2013



First: OUR REAR DIFFERENTIALS WERE NOT ASSEMBLED PROPERLY FROM THE FACTORY
Let me update this - it's not that they weren't assembled properly, but more to do with the fact that clutch type LSDs have the ability to be "tuned" - that is, you can activate and deactivate the plates for varying amounts of lockup. In our case, some of the plates have been deactivated from the factory to reduce noise.

https://www.evolutionm.net/forums/ev...y-factory.html
https://www.evolutionm.net/forums/9410547-post613.html

This is a decent alternative for those limited to stock or STU classes, where you are not allowed to modify your LSD.


Aftermarket Options (NOT stock-class legal):

You can either modify your stock differential, like with TRE, Shep, or Weir, or you can go with a completely separate LSD unit, such as a Cusco, Kaaz, or OS Giken. These separate units are usually more expensive, but you get what you pay for - they're packed with more plates, aka more lockup. Up to you to determine how much you really need.

Stock Modification:

TRE Rear Diff Upgrade
This is a 12 plate modification, the "original" of this modification. Since it's release, it has come a long way and packs a LOT of features besides just the plate upgrades. By far the most popular option thus far. Anyone who's spoken to Jon@TRE can tell you this guy is the man when it comes to drivetrain services.
http://www.teamrip.com/EVOLUTION%20R...20SERVICE.html


Shep Rear Diff Upgrade
Alternative to TRE's. Also a 12 plate update.
https://www.evolutionm.net/forums/ev...rear-diff.html

Weir 12 Plate Conversion
Another option. This is somewhat marketed as a DIY kit, but you can send to any decent trans shop to install it for you as well.
http://www.weirperformance.com/maxgriplsdkits.html
https://www.evolutionm.net/forums/ve...p-lsd-kit.html


These diffs are for purchase as a replacement to your stock core:

OS Giken
As I've seen more recently, this seems to be the king of all the aftermarket options. A ridiculous 28 plates are stuffed into the LSD unit, which can be 'tuned' in whatever way by deactivating some of the plates to control exactly how much lockup you want. Also comes with the springs that the Cusco has in order to control the behavior of the lockup. I believe they say the sheer number of plates also helps with the lockup as well as the longevity and noise.

Cusco Rear Diff Type RS
The Cusco is actually very similar to the OS Giken. Features an almost equally ridiculous 20 plates as well as springs, which work in the opposite way the OSG does. The springs allow for gradual/lower initial torque when cornering/upon corner entry, but still allow for enough lockup on corner exit.
http://www.cusco.co.jp/en/parts_prod...rs_typemz.html
http://www.motoiq.com/magazine_artic...co-rs-lsd.aspx - good write-up for 350z

Carbonetics Rear Diff
The diff has honestly more or less fallen off as far as popularity from what I've seen recently. Their claim was that the material used for the plates allowed for both lower initial torque and greater lockup on exit

Kaaz
This is another good option, although I'm not sure how popular it is with evos. Probably in between the TRE and one of the bigger dogs (Cusco/OSG), and its price reflects that. Honestly, I'd either go with a TRE or jump up to one of the bigger ones over getting the Kaaz.
http://grassrootsmotorsports.com/art...hats-the-diff/ - This is for an S2K, but shows a little bit the differences between stock, Kaaz, and the OSG.



A lot of people said when the later evo 8s and 9s came to America without AYC that it was okay because the top European evos tune the ACD programming to affect handling, and actually completely disable the AYC function. This is only partially true - the European evos still have a much more aggressive mechanical rear differential from the factory which aids in the performance - In other words, an ACD tune is only part of the equation!


Basically,

THIS MOD IS A MUST HAVE FOR USDM CT9A EVOS, which didn't receive the ayc or even the RS 1.5 way. It allows the car handle how it was designed to from the factory. There is literally no other mod that gives the kind of power oversteer that an upgraded mechanical rear LSD does.


PROS:

- Power oversteer! Any of these rear diff options will allow the USDM CT9As to do 95% of what AYC can do, while being a simpler, lighter, and more reliable mechanical solution. Any of the aforementioned rear diffs will provide your car enough lockup to completely turn the car around in a tight corner. I've experienced first-hand power understeer before this mod and power oversteer afterwards, with enough capability to do a 180 if I keep my foot planted.

- With that comes the ability to get on the throttle sooner, as well as take a better line through corners for overall quicker times! The car WILL be faster. For anyone who's dealt with the frustration of waiting waiting waiting until they can get back on the throttle, this is absolutely the solution.

- You can set up your cars suspension for maximum grip rather than trying huge rear bars etc to "artificially" coax the car into oversteering and probably end up making the car slower

- Less wear on your front tires! This has been noticeable for a variety of the evo owners so please comment if you've noticed any (you should) - you can keep the steering wheel straight for longer and let the rear do the turning for your car.

- MORE FUN. Breaking the rear tires loose at will is always fun.

CONS:

- Price - though let's be honest, it's not much more expensive than other parts we've bought for the car. Prices depend on which diff you get.

- Noise - also depending on the diff - you may get increased noise with this diff. Be it a clicking noise all the way to a loud (and violent) banging. Also may get some whining at higher speeds from the diff.

- This mod has little to no impact on turn in. Depending on the initial torque you have set, you may actually even get increased understeer/resistance for turn in. Corner entry is still very suspension setup dependent.


---

No amount of rear sway bars and suspension set ups can fix the mid-exit corner understeer properly - the car was built to have an aggressive rear diff in the back, and i think it's the FIRST handling mod USDM evos should get. The Evo will handle completely differently - the way it was designed to.
The reason I say it's the FIRST handling mod to make is so that every mod in the future can be done keeping this set up in mind.

Post your reviews here!

Anyway, I decided to go with the Cusco Type RS 1.5 way. I had it installed by AMS, who sent it to a special shop to shim the diff properly (required for the cuscos).

Either way, this has been a huge upgrade for my car. I've been autocrossing fairly infrequently as i've been quite busy this past spring and summer, but it has been a great addition for the car. I'm getting power oversteer on corner exit and throttle understeer is no longer an issue for me. I should note that I do get some noise/shaking from the diff at low speed turning, only when I'm on the gas (however lightly). The biggest difference aside from the power oversteer is that when I'm exiting a corner at WOT, the car will actually face and go the direction I want it to go. Before, if I was on the throttle exiting right, the car would *just* slightly understeer left - this is COMPLETELY gone.


edit:

Let me say that I have since had the diff re-shimmed by Jon@TRE, with a custom HD side cover, sight glass, basically the works. This guy is the man when it comes to drivetrain components.

bump

bump would love to see reviews from anyone with a carbonetics

Interesting - subscribed

I run the TRE rear diff and I'm very happy with it. I can't see the point of spending that much cash on a Cusco or Carbonetics. For that kind of money I could have my rear diff rebuilt and tweaked three times by Jon at TRE.

l8r)

IF you can get a hold of him - I couldn't, which is why I went with the Cusco. Got everything shimmed properly by AMS, car is going from shop to shop right now for this and that lol but I am excited to test out my new diff and acd reflash

I've never had that much of a problem getting a hold of Jon - although sometimes it does take a couple of emails and a well-timed phone call or two.

I'm sure you'll love your new setup, though. Nothing better than taking the understeering pig out of your Evo. :)

l8r)

yea it has been great - as more people ahve been looking it up hopefully more people will post their reviews here!

Sheps service is $350, turn around time is less than a week.

I had the rear diff re-shimmed and re-configured to utilize all of the drive and driven plates instead of the nonsense original config from the factory. Night and Day difference on handling and understeer too. Eventually I will be going with the Cusco or Carbonetics 1.5-way diff, but for no, I am very happy. :)

I have seen a couple of different figure thrown around here. So Id imagine its a little over $400 when its all said in done with regards to shipping and all that good stuff?

Does Shep have some type of core exchange policy? Even though the turn around time is quite good I am not sure if I could go for a week...

which service did you go with?

I'm interested in hearing about the oversteer control on the carbonetics one, they claim their material allows for even earlier throttle on apexes than regular metallic rear diffs

I actually had Dogbox Racing here in Jersey do the work on my drive-train, rear-diff included. They basically did exactly what Shep and TRE do with reconfiguring the plates so all of them are in use instead of just the 1 drive and 1 driven. Now all 3 driven and both drive plates are in-use.

Nice thing about Sheps service is that it is $50 cheaper, someone answers the phone immeadiatly and processes your parts in a timely manner. Just had him do a T-case with a Wavetrac, outstanding service and now the car really hooks all four corners:)