dsycks

iTrader: (10)

For you it may in fact make sense. I know that autocross guys do often lift a wheel and I have not given enough study to know if the trade off of lifting that wheel is or is not worth the loss in traction and all that entails. When Daddio goes with a skinny RSB however it makes me feel better about what I think my ideal set up may be.

I think this may be a issue that is not all that directly related to the rear diff however. If you just need one wheel to push better because one wheel is up thats valid (but one may be treating a symptom and not a disease) but how will this mod effect handling?

You are correct that a torque biasing rear diff will act more like an open one with one wheel up. For those of us who are on track and or street who don't (and don't want to) lift a shoe this is not much of a problem.

Sadly Quaife doesn't make a rear diff for the Evo and it seems that clutch packs are the only way to go at this point. In my mind is still seems as if the center diff is where the greatest gains can be made until someone gets crafty and does something new.

point&shoot

iTrader: (3)

But keep in mind that TRE's service costs only $400 (not including shipping), and the GSC 60/40 center diff costs $2000, not including shipping (to TRE or Shep) *and* labor!!!

Also, according to Jon at TRE, the rear-diff re-build will go a long way towards improving corner exit speed on the track. He claims this is the biggest weakness of stock Evo's compared to STI's. The Evo is right on the STI's tail going into the corner, but then it can't keep up on the way out. I had a big long discussion with him about this one day.

I will let you all know what I think when I get it back, but a realistic test may have to wait until April, when the racing season restarts here.

dsycks

iTrader: (10)

I just do not see given the info we have so far how this would make a car turn better. Maybe it does, I just don't see how.

So how does this mod change things? My current understanding is that a stiffer clutch pack would make a car less likely to turn. Am I wrong?

In short I'm asking for better understanding and more info. If folks can provide that I'm very interested.

chrisw

iTrader: (2)

it makes it easier to break the rear lose and go into an oversteer situation. with the rear of the car sliding, it should in theory make the lifting the inside rear a thing of the past.

Dave Mac

iTrader: (2)

Maybe Mark will chime in on this thread? It's best to get the info from someone who is actually using the rear diff mod instead of speculating.

Galant VR-4 #34

iTrader: (4)

Hey KC, It does reduce the need but id still like to have the springs and bars as well, especially the springs.

Marty

dsycks

iTrader: (10)

If this is the case color me not interested. I want more traction and control, not less.

I am hoping someone who has this mod or works a great deal with RWD clutch LSDs chimes in on this. From my time with 240s the drifters wanted the stiff clutch pack LSDs and the track guys wanted the torque biasing diffs.

kekek

iTrader: (22)

I think perhaps there is a little misinformation here. To my knowledge Daddio is running the following diff setup: Front = OEM helical, Center = OEM ACD, Rear = Cusco 1.5 Way (clutch type). Apparently at the Devens NT Mark destroyed the rear diff on corner exits b/c of a) 400 whp and b) the inside rear was in the air. Basically he would get on the throttle with the inside rear still hiked up, evidently the diff wasn't strong enough and failed. One of the reasons he changed to the softer rear bar on day 2 of that NT was an effort to keep the inside rear on the ground and deal with his blown up diff.

Then he added the Cusco rear diff for the DC Pro. All of a sudden his car was pretty crazy and had no problem rotating on-throttle. We didn't talk much beyond that (like where else the diff changed the car).

My understanding of some of the factors that cause rear inside lifting:
1) Soft springs up front can cause the car to "tip over" on the outside front during cornerning, this unloads the inside rear.
2) Lack of droop travel in rear dampers. This doesn't allow the range of movement necessary.
3) Big swaybar in the rear. This reduces the rear suspension's ability to be "independent".

In no way is the rear diff going to get rid of inside wheel lift. That is caused by weight transfer in the corner and the diff has absolutely nothing to do with that. It will help to put more power down before the inside rear hits the ground though. As a side note, if you watch the Street Mod video on YouTube from the 2007 Nats you'll see that EVERY single fast evo has the inside rear off the ground at some point. http://holunfie.blogspot.com/2007/10...treet-mod.html It's just extremely difficult to the keep the rear down and not put HUGE spring rate or bars up front, which ruins the balance of the car, IMO.

The real gain from adding the rear diff is the ability to get into the throttle earlier. It aids in getting the ultra sticky evo rear to break loose and rotate.

My personal diff setup is this: Front = OEM Helical, Center = GSC 40/60, Rear = OEM Clutch type. My thoughts on the GSC center is that it works, but since my car is relatively low on power the rear still does not rotate much more with the 40/60 split. Mind you I have an '03 setup for BSP, car makes approx 300 hp/320tq on 93 on a dynojet. My thoughts on the TRE rear diff upgrade are that combined with the GSC center I should get more on-throttle rotation on corner exit, which means my corner to corner times will drop. The Cusco in Mark's car was quite agressive, so for me the TRE makes the most sense. It's also 1/3rd the price of the Cusco.

Someone asked why I got the GSC Center before doing the TRE rear or Cusco rear. I did it because the car already had a clutch type rear diff and I didn't know Jon was offering the rear diff service at that point. I also know the Sti kicks *** coming out of corners and it's got more rear bias. Now I know the Sti really rotates on corner exit b/c of more than rear bias, it's also got 1) more torque 2) shorter gearing 3) a less grippy (for lack of a better term) rear suspension.

Hope that makes some sense.

John

Drifto

iTrader: (6)

Everything I have read/been told always stated that more "lock" in the diff would diminish turn in but help corner exit. This means the car would be more likely to push initially. This is a reason why Lotus offered no LS option in the Elise for the first couple of years until people whined enough and got Lotus to add the option. From what I've read, Lotus still prefers to sell the Elise without one and reviewers of the car with vs without state that the LS does numb turn-in response.
I'm still on stock sways, but with my coilvers set up the way they are the car's turn-in is excellent and it rotates with heavy throttle application when needed. Never had a problem putting the power down because of a lifted wheel, but I'm sure I'm not on the level you guys are and I track on my street tires as well.

kekek

iTrader: (22)

I guess it makes sense to note that point&shoot, Evolutionary, myself and Daddio are all running 285-30-18 (or thereabouts) Hoosier A6 or Kumho V710. We also have relatively stiff suspension (I know Mark and I do for a fact) and the cars are setup for autox.

markdaddio

iTrader: (1)

What John said above is correct about my using a cusco 1.5 way. It works awesome. It makes a night and day difference in the on throttle handling of the car. If anything it made the car looser everywhere, including corner entry, but I think this is mostly due to the fact that the inside rear tire is unloaded very early in a corner. As John said the front spring rate is the key in that department. Too stiff in front brings on understeer pretty quickly.

BTW, anyone interested in buying a really fast SM evo?

Mark

dsycks

iTrader: (10)

Seems as if we are still talking about two different issues.

1) Lifting a wheel and traction effects of such and general suspension issues in auto-x.

2) The ability of a clutch pack rear LSD to make a car turn.

I am not interested in 1 as it only clouds the ability of us to find out how well the product does what this thread says it may.

I am interested in 2 as I do not Auto-X nor will I be setting up my suspension in a way similar to what is posted. As such I just wanna know what the LSD mod will do in and of itself.

Mark, thanks for the thoughts on the LSD. I know you feel this helped you but you also say you think most of the change was from suspension setup. How much do you think it would help on an open track car? Street?

kekek

iTrader: (22)

There is talk about 2 different issues b/c they are interrelated, as noted by several posters their suspension setup changed after changing the LSD. They probably won't say exactly what they changed since it cost everyone lots of time and $$ to figure it out on their own.

I'm waiting for this to turn into the "What is Mark gonna buy now?" thread.

John

markdaddio

iTrader: (1)

Actually more likely to be a what is Mark gonna sell thread.

prostcj

iTrader: (17)

What kind of labor is involved in removing and installing the rear dif.? Don't plan on doing it myself just a question of the cost.