nix

Can any AutoXers give details about upgrading from GSR's front "open diff" to the RS's standard front helical LSD for AutoX use?

Is it as "magical" as so many magazine "road tests" and "reviews" say?

Description about change of car's setup, handling characteristics, driving techniques etc will be greatly appreciated.

2k4EvoVIII

iTrader: (15)

I personally have not done it but have done allot of research on it. I guess there is a huge difference but when you really start getting into driving hard you start to see a little bit of the ABS issue. This is just from a couple people that i have talked to that have done the conversion. For everyday use they said you wont notice any problems.

Chris

nix

Okay, can you say what you discovered in your research? Pros & Cons about it?

As far as I can tell without trying it "on the road" it's a UK Quaife "TorSen" helical LSD. In use, it allows you to reduce understeer significantly. The RS LSD seems to be even more critical in reducing understeer than upgrading springs and shocks. Only alignment seems to play a greater role in Evo handling; especially REAR "toe" settings. BTW I was lucky enough to get a used RS front transfer case to buy a couple weeks ago.

What is "the ABS issue"? You lost me there!
I would assume that you would switch off the ABS system (make it switchable) when driving hard, except in VERY wet conditions (maybe).

My planned setup:
Upgrade to Evo 6 Tommi Makinen Edition (suspension / brakes / etc)
Install RS front and rear Differentials (road & AutoX use)
Use 4.5xx Crown Wheel & Pinion front & rear for the street / 4.8xx front & rear for AutoX.
Use GSR gear-box for the street / RS gear-box for AutoX.

Care to comment on any/all of the above? I'd prefer to get balanced "user" info before spending unnecessary money on wasted parts.

2k4EvoVIII

iTrader: (15)

Well the ABS issue is that the front LSD confuses the ABS computer. So it tends to lock the wheels up more then if you had no front LSD. From what i hear this is why the RS dont have front ABS along with the MR. I could be wrong there but im pretty sure thats what i was told. For everyday driving of course this wont affect you any but what you are AutoX and you slam on the brakes to make corner you will lock them up.

By the way were did you get the RS TC and if you dont mind me asking how much did you pay? I drag race so the ABS issue wont effect me any. I origionally was going to get the Quiafe lsd but its taking so long for it to be released.


Chris

DaWorstPlaya

iTrader: (31)

The reason the 04 RS don't have ABS is because they have a clutch type mechanical limited slip in the rear, a viscous limited slip in the center and a helical limited slip in the front. This configuration causes confusion for the ABS as each is working independently on their own. In order to use ABS with a front and rear limited slip you need some sort of computer controller center diff. That way the computer is able to extrapolate the data for the ABS. The STi has always had a computer controlled center diff (DCCD) and thus ABS and all 05 EVOs have something similar ACD (even the MR). I don't see what changing the rear diff on your GSR to the RS is going to do, because AFAIK, they are the same. I think this also applies to the gearboxes, AFAIK, they are also the same. Only thing is you can install the RS front LSD and give up ABS, both have their pros and cons. The choice is yours.....

Guack007

Im surprised no one said anything about the loss of steering feel that having a front diff can cause. Since I haven''t driven an RS I cant really compare the two, however the few cars I have driven which were equiped with a front diff had the worst feel ever.

nix

Yup, but I think that you'll find that the much touted US '05 MR will NOT handle as well as an '04 US model RS; especially for competition use. It's just NOT as "chuckable" in a corner. In a recent mag article the "new" ACD (Active Center Diff); when used with the AYC [which is standard in Jap-spec Evo 7s] didn't give quite the crisp handling that was expected. As a matter of fact the new '05 WRX STi was rated HIGHER in handling than the Evo for inexperienced drivers . Note though than for better drivers, the Evo WAS the way to go, and beat the STi hands down. IMHO that gap will be even wider with an RS.

Not quite. The GSR (standard) Evo has the AYC (Anti Yaw Control) in the "wide" alloy diff housing. The RS has a narrower "cast-iron" diff (using longer axles), with a "clutch-type" LSD, like a Cusco or Kaaz unit. MUCH tougher. This is what is used for rallying & circuit racing (and DEFINATELY in MY car.)

The AYC unit from the GSR is fragile (especially for drag racing) when compared with RS diff, and gives notoriously "flakey" handling characteristics. This "flakey" handling was one of the main reasons why the older Evo 6 and Evo 6 TME (6.5) were liked SO much more than the Jap-spec Evo 7. This Evo 7 has BOTH the AYC rear diff AND the ACD with an "open" front diff, which allows 3 driver selected settings (dry, gravel & snow.) However when used TOGETHER they gave peculiar handling to say the least. The newer MR with Super AYC and Sport ABS systems, and front "helical" LSD are MUCH improved... and MAY be better for less experienced drivers, BUT they still are not as "chuckable" as an RS in a corner, as they STILL understeer more than an RS. IMHO the way to go for street, and AutoX use is an RS setup.

"Loss of steering feel" would be noticed if a front "clutch type" LSD was used; like "old-school" FWD cars (Mini etc.) as the LSD "action" is abrupt. The RS has a UK Quaife "TorSen" type LSD (ie "helical" type.) This gives a VERY smooth, progressive LSD action and was HIGHLY praised in the mag reviews; especially for SIGNIFICANTLY REDUCING understeer. (Sport Compact Car - June '04 among MANY others.)

That's my problem. The RS LSD scores high marks in the mag reviews.
I want "real world" USERS opinions and Pros & Cons of BOTH units.

DaWorstPlaya

iTrader: (31)

Hold your horses!!! I just realised that you are posting from another country (Trinidad). We are talking about 2 different specs here. I'm sorry I should have noticed this earlier, but all my points refer to the USDM Evos. We don't get AYC over here. Infact for the US EVO MRs come with the best cornering grip of the bunch ......

nix

I got a deal that's DEFINATELY not repeatable as they are ALL used parts. RS "close ratio" gearbox WITH RS "helical" transfer case (TorSen LSD), + Evo rotors ("slotted" front / standard rear) + Brembo calipers (front & rear) for $1,112 US. For us over here this is a GREAT deal, as these parts are usually MUCH more expensive than that, even if second hand (used).

I also have a standard GSR box and transfer case (open front diff) that I'll keep as spares for my project.

Guack007

I still love the feel of an open diff, in highspeed sweepers it just feel pure. I understand that the torsen style are better at not giving any torque steer, and especially in tight corners (hairpins/autocross), however when Im in a high speed corner I like to know that if I give it gas the wheel isn't going to move. If I could I would probly take the front Helical over not having it, however it isn't perfect and both have advantages. Cant remeber which mag it was but they compared a uk evo8 gsr to our 03 evo8 and said the US evo8 is more communicative and they liked it better.

2k4EvoVIII

iTrader: (15)

MAN HOOK ME UP!!!. That is a great find.

Chris

nix

Then the RS diff causes a "fidgety" steering, it "moves" in highspeed sweepers?

As I said maybe the best set-up IMHO is:
Front & rear RS diffs with Viscous Coupling Center diff (maybe ACD, I don't know for sure.) Basically that is your US Evo RS spec. After US MR reviews, maybe I'll learn about that setup. Possibly front-to-rear adjustable torque-split (ACD) like the '05 STi may be ideal for street use.

chrisw

iTrader: (2)

really?

When I had my STI, the one thing I really liked (outside the torque of the 2.5l) was the action of the front diff when going through sweepers. It was very very predictable.

In a constant radius corner (like a clover-leaf on ramp) I would always have the confidence of the front end pulling like mad... AFter I got the EVO, I imediately noticed the lack of grip from the front end on the same on ramp.

You definately give up alot of grip with the open front diff.

JT-KGY

iTrader: (3)

How about the Quaife front LSD that people are talking about here:
https://www.evolutionm.net/forums/sh...0&page=1&pp=40
???

feldguy

iTrader: (4)

I have done a ton of reading on this...and, to put a limited slip in the front of the vehicle helps greatly, and except in extreme use makes the ABS not as susceptible to confusion as its made out to be. As for hard driving, most dismantle ABS anyway, no? I would, personally, I like it on the road, but even then, it still bothers the hell out of me. I'll never get used to it for super hard driving.