I’m pretty sure all 06+ S4s have the 4:1 center too. I’m not sure of a VIN split or anything though.
When you are turning, you’d like the inner wheel to spin slower than the outer one. Passive mechanical LSD’s are speed equalizing, in that they force the inner wheel to spin the same as the outer, so when you are trying to corner a LSD can actually cause understeer.
But this is the lesser of the 2 evils, since without an LSD you’d have the inner wheel spinning (magnified if you have weight shift and more traction on outer wheels) and becoming a power sink of sorts. Conventional open diffs are torque equalizing, so the outside wheels puts down whatever the inner slipping wheel is putting down. If a wheel ever goes off the ground, you get get effectively nothing out of that drive axle.
This is why many OEM’s are going towards active torque vectoring clutchpack diffs, where you can pro-actively route torque to the appropriate side of a drive axles without messing with their relative speeds.
An LSD is also great for low-mu situations (ice or snow), where you aren’t trying to turn but instead not get stuck.
For an interesting read check out part of the book on the design of the GT-R/Skyline (page 65 of Nissan GT-R Supercar: Born to Race), not sure how well this link will work: http://books.google.com/books?id=0JWlaTqB8V0C&pg=PA64&lpg=PA64&dq=LSD+cause+understeer&source=bl&ots=8v8erasAbZ&sig=Rix8NYhOf7e0ZlJ5b3qN2ykb9xI&hl=en&sa=X&ei=xQUjVJrnM4OOyASwg4G4BQ&ved=0CCAQ6AEwAA#v=onepage&q=LSD%20cause%20understeer&f=false
Since we’re on a subject, what’s the difference between Wavetrac and JHM unit?
Snow driving isn’t effected unless I want it to be. If I turn off the traction control I’m more able to have fun. I still need to do the Scandinavian flick if I want the car tail happy but once it is I can play and control the slide.
Thanks guys really helpful info here. I appreciate all the feedback. Jimmy was great meeting you and slow over the weekend and shooting the shit. look forward to doing it again sometime. Looks like I have some more research to do in terms of which I want to end up with.
That’s a damn good price for that. Is it an off the shelf part or did you guys have to make your own case to adapt to the S4 gear ring?
Yeah that is a great price. Looks like I need to add something to the list.
What do you mean by off the shelf part, like from another car? We had these LSDs made to our specifications.
Installation Note: When replacing the differential, the factory repair manual states that you must check ring gear backlash and bearing pre-load. Our JHM LSD is built to factory tolerances and all the differentials we have swapped at our service facility haven’t required “re-shimming”. However, due to variances in factory tolerances, it is best to make sure that these measurements are checked and confirmed. Additionally, if you do not have the right “bearing splitters” to remove your original bearings with a press, install them on the JHM differential, and correctly inspect for wear or issues you may need to replace the differential bearings. If you have concerns about your tools or your ability to properly inspect and/or disassemble and re-assemble your differential please don’t hesitate to contact us. We can perform all of this work for you if you send us your differential housing.
So how does this affect slow city driving and acute turns? How does it impact overall driving behaviour when not pushing it and making 90+ degree turns at slow speeds?
On top of this, will this effect esp at all? Will it throw the light more often or less? I would imagine less since the we shouldn’t have just one wheel spin in loose corners or something like that.
Waiting for Jake to wake up and chime in on this thread or the AZ one.
This won’t impact ESP. ESP triggers if there is a unbalanced acceleration it uses the maf and a calculation on several other inputs I’m pretty sure you would still need to turn off ESP of you wanted to do donuts like that.
I can honestly say I don’t think I have ever seen a more impressive display of awd audi donuts on dry pavement ever.
Just a friendly bump to remind Jake I’m still waiting for an answer to my question on AZ or here 
Thanks.
And another bump to try and get my question answered
Here is what I got from CV when I asked. He said there is no effect on the interference with traction control. It’s not a clutch style so slow speed driving isn’t effected only when pushed are you going to notice the diff is really there
So when you’re doing a slow acute turn, are the rear wheels going to be turning at different rotational speeds or are they going to be turning at the same rotational speeds? If they’re the same, that’s not going to be weird? I mean, the outside wheel normally has to rotate faster to make up a greater distance even though the angular distance is the same for both wheels.
I apologize for the delay!
The LSD is not going to affect ESP in a negative way. Sure, it may happen less do to the rear wheels not being able to spin as easily. This is also a Limited Slip Differential, not a Posi, so slow sharp turns are not going to be an issue. (I have had posi units in my Camaros and slow turns would make the outside rear tire chirp when trying to turn, you won’t experience that with the LSD).
If you ever in another situation where I am not able to get back to your question as quickly as you would like online, please feel free to shoot me an email directly!
Jake
You will get the outer wheel to travel as long as you don’t give the car too much power. It’s a helical design so it has to have enough force to lock up. The clutch type works close to the same way but the clutch will wear out the helical won’t. Remember it’s a limited slip so it still slips at low speed or low input situations.
I want one.