JHM 4:1 Center Diff Now Available for B6 & 05.5 B7 S4! More power to the rear tires

[jaybquick@JHM]

I can't imagine an S4 with a proper clutch and DR's on all four corners. I would expect short times in the ~1.7 range.

My toy car is a '91 mustang with Al heads, cam, intake and all the supporting mods. I run the MT ET streets and a spec stage II clutch and that car leaves HARD. I dont think i ever did any better than a ~1.85.

My 60fts with my B5 S4 on street tires is in the 1.7 range. With drag radials 1.6s or better should be the expected. On street tires 1.8s to 1.7s are what you aim for. I have a couple times gotten 1.6 60fts on street tires, but rarely.

I have a 91 Mustang as well with a 347 stroker and have had the same tires you ran on it and got a high 1.7 60ft with a full street setup, so I know the feeling.

Whats the average labor hours to install one? thanks

2 to 3 hours depending on cat back and downpipes.

anyone who has this care to comment on how/if it changes the drivability during weather conditions, especially winter? Id assume more power to the rear would alter the driving mechanics. Definately not a bashing question, just wondering.

Here is a nice response from a B5 A4 owner who has had this kind of mod for a while. He posted this in another thread of mine.

I modded the center diff of my A4. There is a difference, but you'll really need to be able to drive the car at 10/10ths to really appreciate what this does for our Quattro cars. If you do this diff without doing a rear LSD as well, the difference will be subtle...simply because you cannot defy physics. Yes, the car will be *MUCH* more neutral going through long-sweepers, but if you have enough weight x-fer away from the inside-rear, you will have some wheelspin (especially if you're packing K04's), which will cause the car to go right back to power-understeer because spinning a tire is taking load away from the rear, putting the torque towards the front.

Even with a K03 in my A4 with R-Compound tires I feel this every auto-x event. Just like anything, you learn to drive around it. But, in all, if you have the $$ to do it...get the rear clutch-pack LSD at the same time. That will allow you to get the most out of the center diff upgrade. I've been itching to find the $$ for me to upgrade to the rear LSD.

Oh...and U-Turns are a riot with the 4:1. In general, the less available grip there is on the road surface/tires the larger the difference is between 4:1 vs 2:1.

est cost for install?

...I may have to take a little drive over there

We do the install for only $200 since it is an in house part. We tend to give better deals on labor for in house made parts. So $200 plus $350 plus about $50 in some new gear oil.

Feel free to call us to come down. 209-968-0077

Jason, for those of us who are local(-ish), is this something we could schedule to have installed while-we-wait? This is just a little too tempting.

Yes we could do it in a 2 to 4 hour period. There are several restaurants nearby. We also around the corner from the ACE commuter train for those who can't find someone to come with them if they need to drop the car for a day or two.

Sounds like the 4:1 diff mod if for those who like carving the corners. Do you need to turn off the ESP to get the advantages of this when in the canyons, or is it rendered not effective if you leave the ESP on?

For track or Autocross, I'd take the ESP off, but when I'm hanging on a canyon edge I leave the ESP on, just in case.

So, is this mod only effective with the ESP off? And, does anyone turn off the ESP when canyon carving?

Generally you will notice this most when you are pushing the car harder than the ESP will allow. However it seems most people are happy with it in most any condition.

On stock tires i am able to cut 1.8s and thats on stock clutch too. So i wouldnt see no reason why one couldnt cut a 1.7 or maybe even better.

Whats the turn around time for someone that has shipped you their diff? meaning how long does it take for you to work your magic?

Same day in most cases.

As for drag racing it depends on your tires and suspension. For cars that don't squat as much using a stock diff tends to be better. If you wanted to put stickier tires in the rear some have found in those cases the center diff does help.

Is it correct that the RS4 is set up stock to send up to 80% of the traction to the rear tires, if needed, during daily driving?

If so, then it sounds like this mod is good for a 2005 S4 which only sends up to 60% (?) to the rear tires, if needed. Is this mod only noticeable when during aggressive twisty road driving IF you turn off the ESP, or noticeable even with ESP on? I usually leave ESP on during canyon driving. Thanks for your input.

From what I have read the 06 and up S4s and the RS4 do already have this mod. (they both share the same part number for the center diff). In 06 the part number did change so there is a difference. Until I get an 06 and up in here to tinker with their trans we are at the mercy of what was claimed. But I would bet that this is really the case.

Will these work for auto and 6spds?

We have all the 6 speeds covered. We haven't looked into this for auto transmission cars yet. Haven't even looked at one. Not sure if their center diffs are built similarly and are as easy to remove. In time hopefully we can check into this.

[nealRlett]

Looks like I am driving up to Lathrop again.