Have you ever had just the tre rear diff without the 40/60 center? If so, could you comment on that at all? I don't think I can afford that. I may get the center diff tune up.. I heard people get a different (ralliart?) limited slip with that too?

 

I don't think there is a ralliart center diff "tune up". Have you been playing too much GT4 lately?? Maybe you are thinking about the front helical diff.

I have had the 40/60 only, 40/60+TRE rear and TRE rear only. The combo is def the most fun and allows you to get in the throttle VERY early and will also help with attitude in longer corners. I would say with my horsepower and grip levels (about 300 whp and 285 autox compound tires) that most of the benefit is in the rear diff though.

Off ramps/on ramps with the TRE rear only & street tires the car is MORE than happy to rotate on throttle. I must say though that the car is on ohlins w/r-compound friendly rates, so it's not shocking the thing slides around alot.

The TRE mod is not difficult and the price/effectiveness are great. On top of it you get someone with decades of drivetrain experience setting it up. I'm not saying it to fluff Jon up, he doesn't sponsor me. I've just done a decent amount of business with him and believe in his work.

If you want another aftermarket diff the Cusco is supposed to be a good unit. Just be aware that installation and setup can be rough. I know someone that had custom spacers machined to fit the diff in the housing since there was no OEM replacement that worked. With the TRE it's more plug & play. Long term the cusco may be better, but I think Jon has seen a couple units come in that are wearing well, so the product is proving itself.

HTH,

John

 

I think I just picked up that ralliart thing skimming another forum about the center diff. But yea, I'm pretty sure I'm just going to be leaving the center diff alone, and using the Tre Rear diff with maybe some PIC TSO coilovers.. I just want the car neutral, without understeer in the corner exits, and I don't like the idea of getting owned in the corner just cuz the X's got some magic diff (getting owned cuz of lack of driver skill is a different story )

 

Yea, I had a "moment" getting on it on an on ramp in Bridgeport from 95 to 25. Brain says, positive camber, pretty wide. Right foot forward, car rotates very quickly, back end goes and I almost kiss the wall. Perhaps you have been on that stretch of road?

 

I grew up in Trumbull. I know the exact exit you're talking about. Alot of the Merritt pkwy ramps are rather "interesting".

 

Thats quite interesting, since the AYC clutch packs are technically seperate from the differential. are the clutch packs taken out? Is there a link for this?

 

i agree with that....

 

I have installed a Cusco limited slip differential into a EVO-7 with S-AYC and the only thing that it's replacing is the factory open differential. The S-AYC is retained but it's not as operational at biasing power to one tire over the other because the limited slip is providing equal lock-up to both tires, kinda fighting against the S-AYC. This is will probably work better than the detuned S-AYC that the EVO comes equipped with but honestly guys S-AYC should be the end all when it comes to making the car behave the way the driver wants.

That being said we should all wish that someone disassembles the ACD and S-AYC so we can dial it in with the ECUFlash software. I feel that there will be huge gains for all once that happens.

 

Agreed, the only options now are replacement ACD ecu's that lock up the rear more via fluid pressure i think, most have given positive feedback on it, so has anyone considered these? I'm talking about the Ralliart and MoTec units, this is not a hardware "in the drivetrain deal, it's a computer swap.

 

I stand corrected, I misunderstood how it all worked. I have been talking to the guys that built the 24hour BritCar Evo X and he had this to say regarding front and rear diffs for the X:

Interesting stuff...and this is the car I am referencing:

 

Hmm.. So what will the ayc be doing that the tre rear diff can't, besides control of all side to side wheels?
I think as long as the rear diff provides that ability to turn mid corner and exit without all the understeer, what more really does the ct9a need to keep up with the new X in corners? Wasn't that pretty much it? The X would rotate/have that rear diff providing that turn where the IX wouldn't, and would understeer?
From what I gathered, the tre rear diff should be an adequate match for it?

 

I wonder if I could, being the OP, throw in the STI's 4wd system as well? Theoretically, it should be better but STI's are ending up characterized as understeering cars. Is that something one can chalk up to flaws in the chassis, or lack of a yaw control system?

 

Meevo:

AYC only operates on the rear two wheels, not all four. It varies power sent to the outside wheel, dialing out understeer via calculations of steering angle, speed, and yaw angle/yaw moment. If Im not mistaken, it can transfer more power to the outside wheel than the inside wheel, which a mechanical LSD cannot do.

The DCCD in an STi is a 35/65 split open differential connected to an electromagnetic limited slip module. In theory, the way a differential operates, the diff will always transfer torque at 35/65 until completely locked ( then it would be 50/50) but the DCCD varries the amount of lockup and changes handling in that sense.

BUT, the DCCD is more akin to the ACD in an evo, as they are both center differentials. AYC is in the rear diff. Subarus understeer just as bad as evos do stock, they have too much weight over the front wheels, blah blah blah. both cars have remedies for this natural understeer quality.

 

Everything I read says that the TRE is a great mod price per performance handling.

Is there a downside ?

For instance: Today it snowed. My Blizzak equipped evo feels way more fwd than my tail happy subi. So: If I, hmmm, 'solid' up the rear dif clutch pak, could there be too much of a good thing?

Is the TRE safe for all season driving ? Is their any downside to doing this mod ?

 

The X chassis by itself is MUCH stiffer, that plays a large role also. But this is all speculation as to how similar they'd be without a true back to back test. Anyone with a stock IX w/TRE diff and a Stock X wanna meetup for a test????????????