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

[jaybquick@JHM]

UPDATE: 4-09-09. We just received a couple core transmissions we bought today. So we have diffs ready to ship out if you want to do the core exchange and not have downtime!



First off a BIG THANK YOU to everyone here in the B6/B7 S4 forum who has called me or emailed me lately with inquiries and praise for our hardwork. For those who's calls we missed, emails or PMs we have been slow to get to we deeply apologize and have some more help coming on soon to keep up. If you do call PLEASE leave a message, we WILL return your call.

Also a special Thanks to the B7 RS4 owners who have called from all over the world asking about our possible future offerings for you guys. We will get to you guys with some cool hardware soon enough. If there are any B7 RS4 owners in the SF bay area or Sacramento Area feel free to contact us to help us with R&D for new B7 RS4 parts.



NOW TO THE NEW PRODUCT.

For Manual Transmissions Only (Please specify in the comments during checkout, the year, model and how many speed transmission your Audi has when purchasing.)



Intro price of $350!


As of 3-27-09 we have the following coverage and cores ready to ship.


- B6 S4 and 05.5 B7 S4 - FVD, HEP, HSM trans codes only (We have Cores in stock!) The 06 and up B7 S4 and the B7 RS4 have a different part number for the center diff and are reportedly already 4:1, we are investigating this further.


ABOUT THE PRODUCT

The factory torsen center differential in the S4 and A4 provides a 2:1 torque distribution between front and rear. What does this mean? This enables the end of the car that still has traction (most of the time the rear) to deliver double the torque to the tires with traction. JHM's experience has found that this closer to even distribution is best for drag racing. So this modification is not for you if you are into drag racing primarily. However for Auto Crossers, Road racers and others who prefer the twisties JHM recommends a bias ratio of 4:1. This is the same bias ratio that Audi has provided in the stock B5 RS4 driveline.


So if you are tired of going through corners while using a lot of throttle and still getting "understeer" then this product is for you and will help you get a little more "oversteer" and allow you to drive the car a little more like a RWD car but still have the superior control of AWD.


For Manual Transmissions Only (Please specify in the comments during checkout, the year, model and how many speed transmission your Audi has when purchasing.)


Core Exchange
There is a core charge of if we send out a JHM center differential to you (see drop box below for amount). When you exchange your center differential for a JHM unit, send your differential back to JHM and we will refund the core charge. $650 core charge, check the chart above to see if we have a core in stock for you.


You may also send your differential to us for modification and not incur a core charge. We can usually modify and ship out your differential within the same day. If you will be sending yours in, unselect the core option and specify in the comments that you will be shipping it in. Also put the invoice number on your box when shipping it in for modification.

Please specify in the comments during checkout, the year, model and how many speed transmission your Audi has when purchasing.



VISIT OUR ONLINE STORE HERE TO ORDER -> http://www.jhmotorsports.com/shop/ca...products_id=46



UPDATE: I had many people asking for instructions. So I used a trans core I had here and some existing pictures and put together a decent instructions for you guys. These should get you through it with not too much headache.

[cabracco85]

Yet another good product from JHM. Cant wait until i have the funds to get one of these on my car. Keep up the good work.

[04v8s4]

So for my own knowledge I'm just going to summarize the improvements of this upgrade. Please tell me if i am off base.

Essentially a torsen diff manages torque imbalances. This is measured as the Torque Bias Ratio. The stock B6 S4 uses a 2:1 TBR. This means the maximum possible torque imbalance is 66%...(2+1 = 3. ---> 100% / 3 = 33.3%. ---> 33.3% x 2 = 66.67%) I suppose this means the diff can only manage/split 66% of the torque in either direction, front or rear? Is this correct?

The JHM upgrade is a 4:1 TBR meaning that the center diff can manage a possible 80% torque imbalance. (4+1=5. ---> 100% / 5 = 20%. ---> 20% x 4 = 80%.)

So essentially this diff can send up to 80% of the available torque to the front or back?

Now this torque imbalance is different from the normal traction situation where the B6 develops a 50/50 split front and rear.

[jaybquick@JHM]

So for my own knowledge I'm just going to summarize the improvements of this upgrade. Please tell me if i am off base.

Essentially a torsen diff manages torque imbalances. This is measured as the Torque Bias Ratio. The stock B6 S4 uses a 2:1 TBR. This means the maximum possible torque imbalance is 66%...(2+1 = 3. ---> 100% / 3 = 33.3%. ---> 33.3% x 2 = 66.67%) I suppose this means the diff can only manage/split 66% of the torque in either direction, front or rear? Is this correct?

The JHM upgrade is a 4:1 TBR meaning that the center diff can manage a possible 80% torque imbalance. (4+1=5. ---> 100% / 5 = 20%. ---> 20% x 4 = 80%.)

So essentially this diff can send up to 80% of the available torque to the front or back?

Now this torque imbalance is different from the normal traction situation where the B6 develops a 50/50 split front and rear.

You got it. Generally it will send the higher percent to the rear due to how the car reacts due to weight transfer on accel, but when under braking more can go to the front at times.

We have noticed a big difference at the drag strip trying stock diffs and then 4:1 diffs. The fronts can spin when it is stock when the car squats. With this mod we have noticed the car could actually fishtail pretty good at times, so we would end up needing better rear tires.

[04v8s4]

Beautiful...thanks for the reassurance.

I guess i was unsure about the 50/50 split which is only true under normal driving conditions where equal traction is present at each wheel. It's only when different wheel speeds / traction conditions are present when the center diff can distribute greater than 50% of the available torque to the front or back.

Thanks...seems like this would be a worthwhile mod for corner carvers.

[jaybquick@JHM]

Beautiful...thanks for the reassurance.

I guess i was unsure about the 50/50 split which is only true under normal driving conditions where equal traction is present at each wheel. It's only when different wheel speeds / traction conditions are present when the center diff can distribute greater than 50% of the available torque to the front or back.

Thanks...seems like this would be a worthwhile mod for corner carvers.

Exactly man. The corner guys generally love this mod. Those who drag race tend to prefer stock diffs and just stick drag radials on all 4 corners. Obviously when drag racing you could run one of these diffs and put sticky tires on the back, but that will really strain the rear diff a lot more. Seen some gnarly results from it too.

[04v8s4]

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.

[pinkslip]

Definitely a worthwhile mod! Great pricing too.

[Monchichi8]

WOW! Yet another Awesome product for our cars! You guys are on Fire!

[beecha91]

Whats the average labor hours to install one? thanks

[RudeBwoi]

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.

[antic]

est cost for install?

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

[pinkslip]

During normal driving, you will still maintain an even distribution of torque amongst all wheels. It is only during aggressive driving/accelerating the torque will be sent to the rear wheels more. The car still handles huge downpours with high honors.

I believe JHM quoted me approximately 2-3 hours labor. Stasis wanted either 4 or 5 hours, IIRC.

[eweu]

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.

[FarmerBob]

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?

[cabracco85]

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.

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?

[Matt@JHM]

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?

The day we receive it we will modify and send it out that SAME DAY.

[cabracco85]

The day we receive it we will modify and send it out that SAME DAY.

Very quick turn around times, keep up the good work

[FarmerBob]

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.

[cabracco85]

Will these work for auto and 6spds?

[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.

[FTYAVANT]

So if you are tired of going through corners while using a lot of throttle and still getting "understeer" then this product is for you and will help you get a little more "oversteer" and allow you to drive the car a little more like a RWD car but still have the superior control of AWD.

I want....

[jaybquick@JHM]

UPDATE: 4-09-09. We just received a couple core transmissions we bought today. So we have diffs ready to ship out if you want to do the core exchange and not have downtime!

Also with these transmissions we are going to be officially offering a transmission rebuild service soon. We can do them now, we are just working out the details. We have been doing this for the B5 S4 guys for years now, so wanted to offer it to you guys.

[cabracco85]

UPDATE: 4-09-09. We just received a couple core transmissions we bought today. So we have diffs ready to ship out if you want to do the core exchange and not have downtime!

Also with these transmissions we are going to be officially offering a transmission rebuild service soon. We can do them now, we are just working out the details. We have been doing this for the B5 S4 guys for years now, so wanted to offer it to you guys.

Sounds good, keep up the good work. I might have to do this mod sometime down the road.

[beemercer]

UPDATE: 4-09-09. We just received a couple core transmissions we bought today. So we have diffs ready to ship out if you want to do the core exchange and not have downtime!

Also with these transmissions we are going to be officially offering a transmission rebuild service soon. We can do them now, we are just working out the details. We have been doing this for the B5 S4 guys for years now, so wanted to offer it to you guys.

Will there be an option for a better overdrive 6th gear with the transmission rebuild kit?

[jaybquick@JHM]

Will there be an option for a better overdrive 6th gear with the transmission rebuild kit?

Yup. I actually found a used 6th gear from a Europe diesel trans today. I got a guy in LA who is buying it from me to test. So we finally might get results on that as well in the real world. It will be an 800 rpm drop at about 80mph.

[sway]

Holy... On it already. Good stuff guys. I have a question on the diff though, I never plan on using drag radials, just street. Will this diff hinder or help my 0-60 ft or mph, if by much? I guess next thing would be to get upgraded rear diffs as well, no?

[fitzS4]

UPDATE: 4-09-09. We just received a couple core transmissions we bought today. So we have diffs ready to ship out if you want to do the core exchange and not have downtime!

Also with these transmissions we are going to be officially offering a transmission rebuild service soon. We can do them now, we are just working out the details. We have been doing this for the B5 S4 guys for years now, so wanted to offer it to you guys.

do you have a ball park range on a tranny rebuild??

[beemercer]

Yup. I actually found a used 6th gear from a Europe diesel trans today. I got a guy in LA who is buying it from me to test. So we finally might get results on that as well in the real world. It will be an 800 rpm drop at about 80mph.

Cool, the full transmission rebuild seems like a much better method of installing the overdrive. To me its a no-brainer if you have to replace a synchro or something. And a 800rpm drop would be awesome, beyond just the better mileage it'd be nice to have the engine at 2000-2500rpm at normal highway cruising just so the engine wouldn't be straining and groaning as much.

[jaybquick@JHM]

Holy... On it already. Good stuff guys. I have a question on the diff though, I never plan on using drag radials, just street. Will this diff hinder or help my 0-60 ft or mph, if by much? I guess next thing would be to get upgraded rear diffs as well, no?

If you put larger rear tires and your car had a tendency to spin the fronts a little then yes it would help. It depends on suspension setup and tires. Traditionally for the drag strip we prefer the stock diff.

do you have a ball park range on a tranny rebuild??

If you sent yours in and no gears or shift collars were damaged (usually due to neglect or shifting with a bad synchro and ignoring the grinding for a long time). I would say in the $2000 to $3000 range. Still pricing out the parts needed and haven't gotten back my european direct prices.

[sway]

i'm trying to get the stasis sL c/o and the rear wheel for the set i'm looking in to is 9.5 for the rear. not sure on tires yet though.

[cabracco85]

Any word on the 6th gear conversion?

[jaybquick@JHM]

UPDATE: I had many people asking for instructions. So I used a trans core I had here and some existing pictures and put together a decent instructions for you guys. These should get you through it with not too much headache.

[jaybquick@JHM]

Any word on the 6th gear conversion?

We have sourced a .56 gear from a European diesel transmission. Just waiting for it to arrive then we need to find a volunteer.

[cabracco85]

We have sourced a .56 gear from a European diesel transmission. Just waiting for it to arrive then we need to find a volunteer.

If i wasnt soo far away i would be down for it. But i dont think it will happen for me atleast until i need to pull the tranny for a clutch job or something like that.

[jaybquick@JHM]

If i wasnt soo far away i would be down for it. But i dont think it will happen for me atleast until i need to pull the tranny for a clutch job or something like that.

Understandable, when the trans is out it is only like a 10 minute job. So it saves on labor time.

[Papachristou]

This is a super easy job on the a4 but it looks like you guys have that damn second exhaust pipe in the way i sure wouldnt mind that though........ it really helps the car stay planted in the rear when powering out of turns and you can get it nice and sideways while the quattro makes you look like a pro pulling out of the slide! one of my fav mods!!!!!!!

[kaiserserser]

This is a super easy job on the a4 but it looks like you guys have that damn second exhaust pipe in the way i sure wouldnt mind that though........ it really helps the car stay planted in the rear when powering out of turns and you can get it nice and sideways while the quattro makes you look like a pro pulling out of the slide! one of my fav mods!!!!!!!

Did you have the rear lsd as well or just the center diff? The review posted above said that unless you had both it would still understeer.

[ngng]

NOw that JHM has cores, tehre is NO REASON you should not do this.