prostcj

iTrader: (17)

Since you have a zero seller rating I don't know if I could trust you not to be a scam artist.

point&shoot

iTrader: (3)

Well you said it's a really fast SM Evo and presumably you own it, so unless you own more than one SM Evo, I think we know what you're selling! :-)

EJEvo

iTrader: (18)

That matches up with what Jon told me. Jon pitched to me as one of the selling points that the modded rear diff would allow you to skip the wildly stiff suspension setups needed to get the rear loose, which those suspension mods in and of themselves bring some challenges and compromises in other areas of driving.

As far as what is necessary to remove the diff, I don't believe it's that difficult. My mechanic charged me 2 hours labor, and said the toughest part is getting the 1st half-shaft out, and then the rest just pops out. I took advantage of the diff being off the car and threw on some Whiteline rear diff bushings. My mechanic said the diff came back from TRE with new seals and otherwise looking like new.

Unfortunately with upstate NY in the firm grip of winter and the Evo shod with winter tires, I haven't been able to take it out and push it to find out what changes can be felt with the new rear diff in place. I can say it made some noise for the first few miles as the thing got broken in (for example, taking a sharp right out of a parking lot while accelerating) - I believe Jon explained it was the shot peened surfaces smoothing off - and of course the stiffer bushings add some.

By the time I get to shake it down this spring, I'll hopefully have a front lsd, rebuilt t-case and tranny, and perhaps a center diff, so I won't be able to isolate the rear diff's impact from those other items.

point&shoot

iTrader: (3)

As long as we're coming clean, my diff setup is: Front = OEM helical, Center = OEM w viscous coupler, Rear = OEM, about to be rebuilt by TRE.

I'm currently running somewhat softer springs then kekek and Daddio (500lbs front, 700 lbs rear), hence I can't lower my car as much as I'd like. In the spring, I'll be switching to a stiffer setup and will then be able to lower the car without an undesirable amount of roll caused by lowering the roll center.

I only have 275HP at the wheels, according to DynoDynamics, and only 258HP, according to Mustang. I know this is kind of low for BSP, but I have an '03 Evo 8, and it doesn't have the advantages of MIVEC and the 10.5 turbo hot-side.

As kekek mentioned, I'm using the same 285/30-18 tire and wheel setup as Daddio, which I shamelessly copied. Thanks, Mark! :-)

dsycks

iTrader: (10)

Guys, please understand that I'm not trying to pry out of everyone what their set up is as I honestly only care in so far as I want to know if this mod will help ME!

I for one do not lift the wheels but I must admit, in the last year of track time, the only time I felt my car was not as fast as I needed it to be was hot on the a$$ of an STI who I could climb up on until mid turn... then he pulled away.

This upsets me as my car never failed at anything else I asked it to do. It's wicked fast everywhere but no matter what I tried I could not keep the STIs from walking away in the twisties. If this diff helped fix that it will be on my shopping list but I am not sure I want to make the car try to break traction in the rear to do it.

In the mean time I am re-evaluation the otherwise stockish suspension setup I'm wearing and how I will be changing things. There are also some power adders in the mix but thats for the 911turbos, GT3s, Vipers and Vettes of the world. What I need most is a car thats faster in the corners and coming out of them.

EJEvo

iTrader: (18)

This is EXACTLY the situation Jon described that this mod would help. I can't vouch for it (yet). I would suggest you put aside 30 minutes (at least!) and attempt to get a hold of Jon and discuss it with him. He's tough to get a hold of, but once you do he'll spend a lot of time with you to discuss it. I'm guessing this is why he's so tough to get a hold of...

He also said it should help rotate the car on the autocross course, so both that and the scenario above gave me enough reason to go for it.

As for the other suspension changes, I'd wait on them until you got the rear diff mod, if you're going to do it, as Jon also said some have found they need to back off changes and make the rear a little more compliant once this mod is in place.

EVOlutionary

iTrader: (38)

Wow, this thread has blown up in the past few days. I will try to answer a couple questions and give a little more feedback. To start with the above questions - in my car the TRE rear diff seemed to make the rear NOT want to turn as easily as the stock diff. That's because the two sides are locked together tighter and it wants to resist the inside and outside wheel speed differences through the corner. Especially on really sticky concrete the car just didn't want to turn. The rear end would hop or bounce through the corner as the sticky tires were forced to break traction. It is like when you have a 4x4 with all the diffs locked and try to take a turn in a parking lot. The tires are forced to scrape over the pavement to make up for the wheel speed difference.

We did a couple things to remedy this. First, we added some LSD additive/friction modifier. 2nd, we put some more miles on the diff and it seems to have started to loosen up a bit. Third, Nationals is on slick asphault. There is so much less traction there than on airport runway concrete that the rear tires could slide just enough to make up that wheel speed difference without the "hopping" we were having on concrete. As far as making the car turn better, I would say that on our car that after we got things worked out it probably got TO the apex just as fast as before, but it was faster from that point on because we could put the power down.

Now, on to the topic of inside rear wheel spin. Whether your tire is 6" off the ground or just barely touching, I don't think there will be a noticeable difference in performance (other than the split second it take for the wheel to travel that 6" once you start to transfer weight back to that corner). The key here it NOT in the rear spring rates, the rear diff, or rear sway bar. Once your tire gets unweighted, none of those will make a bit of difference. Personally, I don't think that rear droop travel is the problem either. To get to the same ride height you could run a long 200# spring with 6" of travel, or you could run a more appropriate shorter, stiffer spring with a helper spring. The first option, really long soft springs (think baja trucks) won't work. I don't think the second option will have much benefit either - really, how much traction can you get by pushing the tire into the ground with a 25 or 50 pound spring?? I doubt enough to hold back 300-400 ft# of torque. I believe the key is in the FRONT springs and sway bars. Picture a car coming into a corner. Imagine it rolling about the diagonal axis defined by the inside front (IF) tire and outside rear (OR) tire. Both of these stay firmly planted on the ground while the outside front (OF) dives and drives that tire harder into the ground and the inside rear (IR) lifts and pulls the tire off the ground. In order to keep the IR on the ground you need more spring force at the OF to push the car back closer to level. This can be via stiffer springs or stiffer front sway bar. Now, when you try to accellerate - you can. That's how I think about it anyway. . .

EVOlutionary

EVOlutionary

iTrader: (38)

The above was all in the context of autocrossing. I would not necessarily say the same would hold true in road racing as I have never done it. . .

dsycks

iTrader: (10)

That makes more sense and fits with my understanding. Thank you for the clarification and input.

EVOlutionary

iTrader: (38)

But, don't forget - this is a clutch pack diff with profiled ramps I believe. If the stock diff is a 1.5 way (softer lock on decel, stiffer lock on accel), I bet Jon may be able to reprofile the ramps so you could still get more lock on accel (help corner exit) with less lock on decel (not hurt corner entry). It would be worth you talking it over with him to see just what he is able to do. . .

dsycks

iTrader: (10)

Honestly I think it's in my best interest to put my mod money into a lot of other things before I go down this road.

When I do, I hope there is a 40/60 center and torque biasing rear in the tea leaves because that would be simply sick as he!!.

point&shoot

iTrader: (3)

What you're saying makes perfect sense if the inside-rear wheel is only lifting on corner entry. But mine is off the ground in steady state cornering, and doesn't set back down until I throttle out of the turn. In my case, I'm pretty sure it's because of my upgraded rear sway bar, which is a 25mm adjustable bar where the softest position is about 1.75x the stock sway bar. That's why I'm thinking of going back to the stock rear bar. After all, you have to ask yourself what you're trying to do with a sway bar -- if you're trying to adjust the front/rear balance of the car, okay, that's a valid goal, but once the rear wheel lifts, you've exceeded the range of adjustment. And if you're trying to decrease roll in cornering, well once you've gone to 700-900 lb springs, you don't have significant roll anyway.

As for the rear diff making it harder to turn, that's only a problem when both rear wheels are on the ground! Seriously, I am now wondering what will happen with this diff on corner entry. I guess I'll find out in about a week.

markdaddio

iTrader: (1)

you will find that on low grip conditions you will see a bit more understeer on entry, but in normal grip conditions, it should be minimal unless you are running more than 800lb/in front springs.

theblue

iTrader: (1)

what about going stiffer on the front sway bar? I thought I saw a thread on how to drill new holes on the front one to set it tighter?

also, in my scenario. I have buddy club coilovers with 700 front, 900 rear.. I don't lift a wheel, but I have poor rotation and turn in... My thought it go with sway bars and adjust up until I start to lift a little then back off on the rear sway setting.

thoughts?

Ps. I'm 80% track days, 20% autoX

Erik@MIL.SPEC

iTrader: (94)

Correct me if I'm wrong, but since the upgraded rear diff helps the car rotate, wouldn't that allow you to set-up the suspension for max grip (instead of requiring a stiffer sway bar to help rotate the car which might lift the inside rear wheel)?