Take my commentary with a grain of salt because it's not from an Evo platform, but I swapped in an Evo 8 rear diff with the 12-plate weir package into my 99 Eclipse GSX time trial car. Prior my car didn't really produce oversteer on throttle in most cases (of course with weight shifting I could get it to happen). With this setup holy crap my car scared the **** out of me. I'm not sure yet if it was my lack of driving ability or what but the car became very scary to drive. Felt like I was threading the needle. The speeds though are 120+ turns where I noticed it (lower speeds i'm not sure i noticed much difference, but I just might not have adjusted my driving to get the new diff to kick in), where prior I could get on the throttle a decent amount at apex but now the rear felt like it was on glass when I went into the throttle. I don't know though if this netted a faster lap time as I had changed so much simultaneously with the rear diff (though I did net about 3.5 seconds faster a lap this trip than last), but it did make the car a bit hairy to drive. I added more rear wing which seemed to help but wasn't satisfied at the end of that day, and next time out I'll try even more rear wing.

I wonder if perhaps the locking is too much for my current configuration, and this thought comes from reading about tuning rear differential locking torque on various websites. I'm still running street tires (Nitto NT05), albeit 285 wide ones, but only maybe had 350 wheel torque during that outing. I'm going to give it a few more track sessions before i decide what to do, though I'm considering inverting a few of the plates (similar to how the US evo rear diff comes stock) to remove some of the locking torque. I'm also tossing around going to 315 tires with r-compounds and if I do may delay any differential changes as that may make this setup work better.

Does anyone else have high speed track experience with the weir upgrade?

 

Can't comment on the weird upgrade on high speed track, but awesome commentary - loose is fast

I can only imagine that this mod would work just as well if not better for the GSXs

 

just purchased the TRE 12 plate (w/ $260 additional Ninja side cover) after I racked my car into a high curb trying to be the Stig. Anyways it should get here this weekend and I hope to have my car running soon after, Ive changed from factory wheels and suspension to 17x8 RPF1s and AWD spec D2 coils but i will write a review on how everything preforms.

 

Extra NVH is said to be nil, and caster is something the Evo desperately needs. This just makes the steering BETTER, removes the dead zone in the middle, also removes a lot of the annoying tramlining and bumpsteer.

You don't have to rearrange the rear plates to re-gimp it back to stock levels. Just use more friction modifiers or the Diaqueen fluid.

I think you should perhaps add a bit of toe-in to the rear if you feel that it is too twitchy. If you are running zero toe, try 0.10 or 0.20 degrees of toe in. YMMV but this may make you feel more confident in high speed corners. Take with a grain of salt as I am more familiar with what works on creating confidence on a RWD car, perhaps using more toe-in on an Evo with a modded rear diff won't help much? Worth a shot.

Far better suspension/handling gurus on this site than I, so again, grain of salt.

Any reason why you did 17x8 instead of 17x9 RPF1's? 17x9 is not only concave but also has a lot more grip than the 17x8 while weighing hardly anything more.

 

Any reason why you did 17x8 instead of 17x9 RPF1's? 17x9 is not only concave but also has a lot more grip than the 17x8 while weighing hardly anything more.[/QUOTE]


I went with 17x8 because I got them with 0 damage and with 90%+ new tires Potenza RE01RS I think they are called for $800. I couldnt pass it up. Trust me I want 17x9 bad. Im gonna run these tires then sell these for nearly what I gt them fr and pick up 17x9s later.

 

Interesting - I'm following a few other threads on the matter that say the exact opposite - increases bumpsteer, slows the steering, and numbs the deadzone further (but obviously agrees about the benefits of increased caster, and more or less outweighing any of the cons). I did here the PSRS increases NVH a small amount, as you would expect.

https://www.evolutionm.net/forums/mo...autocross.html
https://www.evolutionm.net/forums/ev...vs-caster.html

These are the threads I have been following about it for some time now.

 

All of those threads pretty much agree the PSRS makes the steering better and the car handles better.

Also, big aside: I took my car out to a massive parking lot last night to test out the rear diff. I also took out a stock suspension/stock diff Evo 9 to compare and contrast (note: Evo 9 was on ****ty tires, I am on great tires).

On my car: perfectly controlled power sliding and drifting with the front wheels pointing your car to where you want to go. Feels ****ing amazing and completely controllable. The way the car should have been!

On Evo 9 with stock rear diff: Tons of understeer and the only reason it slid (it slid sideways, pushing) was because of the tires. Completely different and no true controlled oversteer.

Conclusion: Rear diff upgrade is amazing and everyone should do it.

 

All this and no GoPro!?!?!

 

I did a bunch of changes all at once, so interpret as you will:

Stock KYB w/ WL 24mm RSB (set soft), Michelin Pilot PSS 235/40-17's
--->
GTWorx/HD, RCK, offset PSRS, new stock front strut mounts.

The very light and kinda magical steering went away and was replaced with a heavier, slower wheel with more 'feel'. I did miss the lighter steering at first, but it doesn't bother me anymore. The PSRS is only designed to add 0.5* caster, their web site is incorrect per tech support; I got 0.6* with all my changes. I can say how much of this is attributable to the RCK though.

With just the RSB rear wheelspin was horrible and the car was much slower for sure. It makes me wonder why people are all fired up on it as a mod. I'm thinking a FSB would be a better change.
After everything, now I'm just suffering moderate steady state & exit understeer which I'm hoping the re-stack will help cure.

 

Very tempting, considering I live about half an hour away from Weir.

 

You're thinking is correct, especially if the two are combined (read: FSB and rear diff upgraded). With those two in place, RSB upgrade becomes strictly optional, IMO.

l8r)

 

So I'm still on the fence with this potential mod. My concerns are noise and steering response with/out a RSB
I'm not looking forward to the noise with the restack.
I understand that if friction modifier is used that it will be quieter and not "work" as well. Lets say that its pretty loud with diaqueen/1 bottle of friction modifier and I decide to add another bottle. Can we all agree that a restack with 2 bottles of friction modifier is still going to lockup better then the factory incorrect stack with Diaqueen?

Also, I have a RSB on soft and the ACD Tuning Flash(This worked really well,highly recommend it) The initial turn in of the car is good but it does push a little. I don't like giving up more grip with the RSB on harder settings and prefer the soft setting. I'm somewhat worried about what is going to happen with the restack and the RSB. Possibly too much oversteer/rotation.
Are most people still running a RSB and the restack?
How much does the RSB affect initial turn in?

 

IMO noise isn't worth considering as a factor against doing the restack. The only time I heard it was at full steering lock, and that was only for the first week or 2. Since then I've never heard anything.

 

Fully agreed with Raptord, restack has been silent.

 

Restacked and use Diaqueen with no additional friction modifiers and its been silent since installing...and with oversteer.