Originally Posted by donour

My shep diff has been in for about 5 days. I've done about 400 street miles on it and 2 autocrosses. The original unit had 70k miles and was slipping badly (lots of inside rear wheelspin) -- more on that later.

Installation:

Easy enough, assuming you know, or can figure out, how to remove the rear pumpkin. The unit was returned to me in a brand new box, power coated. I opted for a 12 plate upgrade on the recommendation of trevor. I didn't really spend much time considering different options. I just knew I wanted more lockup in the rear. Total cost of rebuild, bearing replacement, and shipping was around $450.

Noise:

As mentioned in an earlier post. I filled the unit was OE diaqueen. I heard three clunks as I rolled out of the garage and nothing since. Seriously, zero noise. I still use the original rubber bushings and mounting hardware. All things considered, my car isn't very quiet. I have an open exhaust, intake, and no sound deadening. I can hear my walbro fuel pump, but not the diff. *shrug* In my case it wouldn't matter. I don't take the evo to the store.

Street Performance:

It's hard to know what to say here. It's not possible to _really_ push this car on the street. Throttle application result in significantly more rotation than before. The way my car is setup it will step out in any gear. It's not dangerous though. It won't snap. If you can drive a z06 without spinning at every right turn, then you can drive this. I made a quick road trip last weekend for an autocross. On 400 treadwear tires, I could still make the car push -- especially at turn-in. It's not something you'd experience in on-ramp driving.

Autocross performance:

My setup is not stock and I'm not a secretive guy. I'm running Zzyzx EM sport coilovers. They rock, but are completely unobtainable at this point. It sucks to be you. Springrates are 700F/1000R, with a larger front bar and stock rear bar. Those aren't typos. Camber is around -3.1 F / -1.2R. Zero toe. On crappy street tires (above) the car is an oversprung mess. All you can feel is the sidewalls flopping around. On race tires, the car works -- o brother does it work. I'm running cams, E85, and a stock 9.8cm turbo. It makes 300 and something horsepower. 350, 375. I dunno. It's not a dyno queen. My 5400' dyno chart would be useless to most people.

Now this whole process began because of a problem after midcorner. I'll call it 2/3 corner. Any appreciable throttle application at 2/3 corner would result in significant inside rear wheelspin. It took a while (30-40 runs) to diagnose and confirm that it was that wheel and repeatable. The rear wheel was unweighted enough -- and the diff was slipping enough -- that the available traction barely exceeded the scrub of the last 1/3 of the corner. There was a very noticeable point when the wheel loaded back up and the car took off. By that time you were near the exit though.

With the rebuilt diff, this problem is gone. On power, the rear end locks up and power goes straight to the pavement. Excess throttle will still spin the tires, but the rear end will step out rather than just make smoke. Consequently, corner exit understeer has been eliminated in my case. I wasn't really aware of this fact at the time, but I did 10 runs last weekend. There wasn't a single time that I had to get out of the throttle to tuck the nose back end. So cool.

The rear question is if it is faster. I'd like to scream an emphatic "yes", but I can't. Last weekend's event was an Rocky Mountain SCCA divisional. Attendance was somewhat low, but the quality of drivers was very high. I was running about 95% PAX times of several national champs. However, that's what I've been running all season. In class, I've run against the same driver 9 times this season. We are usually within about a tenth of each other. I won, but only by 67/1000s. The data isn't there.

There is no doubt that the car is looser. On the first day I nearly spun out of the start gate because I was used to using full throttle on cold tires. I can't anymore. Although, I never actually looped it so *shrug*. The second day felt much better, but I had probably adapted my driving.

For cars with chronic exit understeer, I would say this a "must" mod. For racecars, where time trumps all, it's more complicated. It will depend on specific setups and driver preference. I have never liked a very loose car. That data has not proven that it is faster for me. More fun: yes. Faster: maybe.

I haven't tried the new setup on the road course yet. Maybe this weekend.

donour


UPDATE: This week, I put the car on the alignment rack. I found out that the rear was not at 0 degrees toe like I had set it. The rear was toe'd out about 0.3 degrees total. For those of you doing mental math, that's a lot: around 3/16. That explains much of the loosey goosey behavior. Oops.

I set the toe to 1/16" in and the rear camber to -1.4 degrees. I took it out to the road course for some laps this morning. I don't know how many I did -- a tank of E85 worth -- more than a handful. I was on crappy street tires so grip levels were low, low, low. As marshall predicted, midcorner push returned. However, exit inside wheelspin was still gone. Hooray, it works. The toe in made catching entry oversteer easy-peasy. The only way to really move on those terrible tires was to throw->catch->accelerate. For a little while, the ferrari club was on track with me. They stayed FAR away.

Tomorrow I'm going back out, but this time I'm bringing kumho 710s and timing equipment.

Originally Posted by TommiM

I just got back from an autox today. The layout was .75 mile long but first half was pretty much 1st gear for me. The layout today was nice becuase of the tight slow turns I was able to test the acd flash lock issues with the tre diff. Interesting that alot of the binding issue was gone since the tre diff was installed. It really seems like the tre rear diff, along with the redline 75w140NS, which doesnt have friction modifiers, overcame the acd flash binding issue. I am not sure how much of this is also attributed to a diff fluid with no friction modifiers. It was intersting that the only time I noticed a binding issue this time was when I was overdriving the car into a turn. Had I taken the correct line I would have been faster and with no binding btw.
This was the first time out using a diff fluid with no friciton modifier and imo,it really helped keep my times consitent all day. Mid corner and exit turn, the car really felt like a rwd car. I could easily blip the throttle and snap the rear end. Fastest times of the day I was running 39 psi fronts, 37 psi rears on dunlop star specs. For now I would say my issue with my current setup is still initial turn in seems not as responsive and still working on that. Maybe fsb or perrin psrs setup willl help out. At this point I would say my car is setup really neutral mid corner and corner exit. The weather today was in mid 70s and I am running 255/35/18 street tires. I honestly feel that for my setup I would not run a wider tire, I was nowhere near overheating my tires even the few times I was overdriving them.

Originally Posted by donour

second update to my review post, with final verdict.

Originally Posted by donour

My shep diff has been in for about 5 days. I've done about 400 street miles on it and 2 autocrosses. The original unit had 70k miles and was slipping badly (lots of inside rear wheelspin) -- more on that later.

Installation:

Easy enough, assuming you know, or can figure out, how to remove the rear pumpkin. The unit was returned to me in a brand new box, power coated. I opted for a 12 plate upgrade on the recommendation of trevor. I didn't really spend much time considering different options. I just knew I wanted more lockup in the rear. Total cost of rebuild, bearing replacement, and shipping was around $450.

Noise:

As mentioned in an earlier post. I filled the unit was OE diaqueen. I heard three clunks as I rolled out of the garage and nothing since. Seriously, zero noise. I still use the original rubber bushings and mounting hardware. All things considered, my car isn't very quiet. I have an open exhaust, intake, and no sound deadening. I can hear my walbro fuel pump, but not the diff. *shrug* In my case it wouldn't matter. I don't take the evo to the store.

Street Performance:

It's hard to know what to say here. It's not possible to _really_ push this car on the street. Throttle application result in significantly more rotation than before. The way my car is setup it will step out in any gear. It's not dangerous though. It won't snap. If you can drive a z06 without spinning at every right turn, then you can drive this. I made a quick road trip last weekend for an autocross. On 400 treadwear tires, I could still make the car push -- especially at turn-in. It's not something you'd experience in on-ramp driving.

Autocross performance:

My setup is not stock and I'm not a secretive guy. I'm running Zzyzx EM sport coilovers. They rock, but are completely unobtainable at this point. It sucks to be you. Springrates are 700F/1000R, with a larger front bar and stock rear bar. Those aren't typos. Camber is around -3.1 F / -1.2R. Zero toe. On crappy street tires (above) the car is an oversprung mess. All you can feel is the sidewalls flopping around. On race tires, the car works -- o brother does it work. I'm running cams, E85, and a stock 9.8cm turbo. It makes 300 and something horsepower. 350, 375. I dunno. It's not a dyno queen. My 5400' dyno chart would be useless to most people.

Now this whole process began because of a problem after midcorner. I'll call it 2/3 corner. Any appreciable throttle application at 2/3 corner would result in significant inside rear wheelspin. It took a while (30-40 runs) to diagnose and confirm that it was that wheel and repeatable. The rear wheel was unweighted enough -- and the diff was slipping enough -- that the available traction barely exceeded the scrub of the last 1/3 of the corner. There was a very noticeable point when the wheel loaded back up and the car took off. By that time you were near the exit though.

With the rebuilt diff, this problem is gone. On power, the rear end locks up and power goes straight to the pavement. Excess throttle will still spin the tires, but the rear end will step out rather than just make smoke. Consequently, corner exit understeer has been eliminated in my case. I wasn't really aware of this fact at the time, but I did 10 runs last weekend. There wasn't a single time that I had to get out of the throttle to tuck the nose back end. So cool.

The rear question is if it is faster. I'd like to scream an emphatic "yes", but I can't. Last weekend's event was an Rocky Mountain SCCA divisional. Attendance was somewhat low, but the quality of drivers was very high. I was running about 95% PAX times of several national champs. However, that's what I've been running all season. In class, I've run against the same driver 9 times this season. We are usually within about a tenth of each other. I won, but only by 67/1000s. The data isn't there.

There is no doubt that the car is looser. On the first day I nearly spun out of the start gate because I was used to using full throttle on cold tires. I can't anymore. Although, I never actually looped it so *shrug*. The second day felt much better, but I had probably adapted my driving.

For cars with chronic exit understeer, I would say this a "must" mod. For racecars, where time trumps all, it's more complicated. It will depend on specific setups and driver preference. I have never liked a very loose car. That data has not proven that it is faster for me. More fun: yes. Faster: maybe.

I haven't tried the new setup on the road course yet. Maybe this weekend.

donour


UPDATE: This week, I put the car on the alignment rack. I found out that the rear was not at 0 degrees toe like I had set it. The rear was toe'd out about 0.3 degrees total. For those of you doing mental math, that's a lot: around 3/16. That explains much of the loosey goosey behavior. Oops.

I set the toe to 1/16" in and the rear camber to -1.4 degrees. I took it out to the road course for some laps this morning. I don't know how many I did -- a tank of E85 worth -- more than a handful. I was on crappy street tires so grip levels were low, low, low. As marshall predicted, midcorner push returned. However, exit inside wheelspin was still gone. Hooray, it works. The toe in made catching entry oversteer easy-peasy. The only way to really move on those terrible tires was to throw->catch->accelerate. For a little while, the ferrari club was on track with me. They stayed FAR away.

Tomorrow I'm going back out, but this time I'm bringing kumho 710s and timing equipment.

UPDATE2: Ok. As promised, I was back out today. Same track as yesterday, but this time with the PCA. They (we) ran a high-speed autocross/DE hybrid course. Luckily the configuration was almost exactly the same as an event I ran last month.

On race tires the car is much, much better. Like my original impression, the difference is phenomenal. Small change in the rear alignment (-1.4 camber, 1/16" toe in) settled the rear down tremendously. Again, I'll say it's 100% more fun. Corner exit is more controlled and exit speed is higher. I'd even go so far as to now say the car _is_ faster. The delta from a well established local field is 4-5 tenths out of 85 seconds. Depending on how competitive you are, that could be tiny or small. For me that's huge and a no-brainer for the price. I can point to the exact places where I picked up time and another, very experienced, driver backed it up with almost identical times.

Final Verdict. It's not magic, but it does help. If you can't identify why you need it done, then you probably can't take advantage of the extra lockup.

Originally Posted by donour

second update to my review post, with final verdict.

https://www.evolutionm.net/forums/8607466-post155.html

Originally Posted by kyooch

also, what setting did you put the acd in? circuit, street or rain? and you have the race flash correct?

Originally Posted by kyooch

very nice - though the improvement from the rear diff is a little less than what we've seen average (most people say 1sec/60sec, depending on course layout). As I'm sure everyone knows, exit speed out of the corner is hugely important, so any improvement in that field will result in a higher speed and lower times overall

Originally Posted by donour

Good points, but here you should note the level of prep. There would probably be larger gains on a stock car, or one that had very limited suspension modifications. I believe this is the case with Marty's T2 car.

d