GT3 differential discussion and service
02-12-2010, 05:23 PM
#1
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GT3 differential discussion and service
A few observations on limited slip differentials
The Porsche 996/997 GT3 street car is a marvelous product for street driving enthusiasts who also enjoy weekend track events and or occasional club races. A great chassis coupled with plenty of power makes for a great driving experience. However, all of that horsepower doesn't matter if you can’t get the power down. The power from these cars when accelerating off corners causes the inside, or unloaded tire to loose traction; this slows the rate of acceleration, causes unwanted corner exit oversteer, and kills the rear tires. The problem only got worse when the newer 997 GT3 was made available. An even stiffer chassis platform and more power put more demand on the already limited-limited slip.
In the past, we used torsen or torque-sensing differentials, made by various manufacturers, Gleason and Quaiffe being most familiar to correct the loss of traction. These differentials seemed to be the end-all. After all what could possibly be better than a unit that actually sensed the torque, and applied it opposite to the wheel that slipped? The key with torque-biasing differentials is that the wheels must remain in contact with the pavement; even a minuscule amount of traction is needed to engage the diff. Early 911's flexed enough and kept the rear wheels on the ground maintaining the miniscule amount of traction needed (just look at the inside front tires off the ground in older 911s when racing). When the 944 turbo came around, with its stiffer chassis, cars would lift a rear tire in tight or bumpy corners and the torque sensing diffs were no good. We learned this first hand when we built the first Mini Cooper S's for Grand Am. Same problem with front wheel drive, when one drive wheel looses contact with the track, say over a curb or bump, all the torque went to that wheel.
Moving onto the GT3’s and their limited slip differentials. A limited slip is a clutch type differential that, with stiff chassis 996/997 based cars, over curbs and in corners, is designed to apply the same force to both rear wheels. Porsche uses a four clutch disc pack in all GT3's. If you jack up one side of a GT3, put a torque wrench on one rear wheel axle nut, you may find it takes less than 20 pounds feet of torque to turn one rear wheel. That's called the breakaway torque. And, that's on a brand new 997. We have checked the differential breakaway torque on two dozen 996/997 GT3 street cars and after one or more track weekends the preload torque is at or near zero. Keep in mind, there are ramps inside the differential that, when drive, or accelerating force is applied, it forces the differential clutches to bind up and act to lock up the rear. However, little or no lock up occurs on deceleration. So, on hard braking, as the weight goes to the front wheels the rears get light, and the inside rear wheel will temporarily lose traction. This causes a slower entry into the corner and generally you will feel the anti-lock brakes engage when this occurs. But what if we could get the differential, to partially engage on deceleration and engage more aggressively the harder we accelerate off a corner, this would be having your cake and eating it too, wouldn’t it? You bet it would!
The expensive solution was discovered by all of the long distance enduro GT3 Cup cars years ago. Install a billet, fully adjustable Guard limited slip differential. This nearly indestructible unit is also available for the street cars. Keep in mind, this solution requires removal and disassembly of the entire transaxle. However, the cost of the unit and labor can exceed $7500. This is a bit of over kill for street, track days and even club racing. The expense of the billet housing is way beyond most club race GT3 budgets.
However, using the same technology and top quality parts we can improve your differential beyond its original ability, and make it last for many track days. We can remove your differential (without removing the entire transaxle) and build the same adjustable ramp diff as the pro's have. The adjustable ramps in this unit allow for 40% lock on acceleration and 60% on deceleration. For more aggressive situations the same diff can be set to 50% acceleration and 80% deceleration. The friction plates in the new diff are far stronger than the Porsche factory parts and won't show near the fade. The break away torque is set to 80 pounds feet new, and after a few track miles they settle in at around 60-80 pounds.
-Mike Bavaro
Visit our website for more technical info then call or e-mail me if you need more specifics or to schedule your GT3 for an improvement way beyond the $3,000 cost of the job complete.
http://www.bodymotion.com
The Porsche 996/997 GT3 street car is a marvelous product for street driving enthusiasts who also enjoy weekend track events and or occasional club races. A great chassis coupled with plenty of power makes for a great driving experience. However, all of that horsepower doesn't matter if you can’t get the power down. The power from these cars when accelerating off corners causes the inside, or unloaded tire to loose traction; this slows the rate of acceleration, causes unwanted corner exit oversteer, and kills the rear tires. The problem only got worse when the newer 997 GT3 was made available. An even stiffer chassis platform and more power put more demand on the already limited-limited slip.
In the past, we used torsen or torque-sensing differentials, made by various manufacturers, Gleason and Quaiffe being most familiar to correct the loss of traction. These differentials seemed to be the end-all. After all what could possibly be better than a unit that actually sensed the torque, and applied it opposite to the wheel that slipped? The key with torque-biasing differentials is that the wheels must remain in contact with the pavement; even a minuscule amount of traction is needed to engage the diff. Early 911's flexed enough and kept the rear wheels on the ground maintaining the miniscule amount of traction needed (just look at the inside front tires off the ground in older 911s when racing). When the 944 turbo came around, with its stiffer chassis, cars would lift a rear tire in tight or bumpy corners and the torque sensing diffs were no good. We learned this first hand when we built the first Mini Cooper S's for Grand Am. Same problem with front wheel drive, when one drive wheel looses contact with the track, say over a curb or bump, all the torque went to that wheel.
Moving onto the GT3’s and their limited slip differentials. A limited slip is a clutch type differential that, with stiff chassis 996/997 based cars, over curbs and in corners, is designed to apply the same force to both rear wheels. Porsche uses a four clutch disc pack in all GT3's. If you jack up one side of a GT3, put a torque wrench on one rear wheel axle nut, you may find it takes less than 20 pounds feet of torque to turn one rear wheel. That's called the breakaway torque. And, that's on a brand new 997. We have checked the differential breakaway torque on two dozen 996/997 GT3 street cars and after one or more track weekends the preload torque is at or near zero. Keep in mind, there are ramps inside the differential that, when drive, or accelerating force is applied, it forces the differential clutches to bind up and act to lock up the rear. However, little or no lock up occurs on deceleration. So, on hard braking, as the weight goes to the front wheels the rears get light, and the inside rear wheel will temporarily lose traction. This causes a slower entry into the corner and generally you will feel the anti-lock brakes engage when this occurs. But what if we could get the differential, to partially engage on deceleration and engage more aggressively the harder we accelerate off a corner, this would be having your cake and eating it too, wouldn’t it? You bet it would!
The expensive solution was discovered by all of the long distance enduro GT3 Cup cars years ago. Install a billet, fully adjustable Guard limited slip differential. This nearly indestructible unit is also available for the street cars. Keep in mind, this solution requires removal and disassembly of the entire transaxle. However, the cost of the unit and labor can exceed $7500. This is a bit of over kill for street, track days and even club racing. The expense of the billet housing is way beyond most club race GT3 budgets.
However, using the same technology and top quality parts we can improve your differential beyond its original ability, and make it last for many track days. We can remove your differential (without removing the entire transaxle) and build the same adjustable ramp diff as the pro's have. The adjustable ramps in this unit allow for 40% lock on acceleration and 60% on deceleration. For more aggressive situations the same diff can be set to 50% acceleration and 80% deceleration. The friction plates in the new diff are far stronger than the Porsche factory parts and won't show near the fade. The break away torque is set to 80 pounds feet new, and after a few track miles they settle in at around 60-80 pounds.
-Mike Bavaro
Visit our website for more technical info then call or e-mail me if you need more specifics or to schedule your GT3 for an improvement way beyond the $3,000 cost of the job complete.
http://www.bodymotion.com
02-12-2010, 08:54 PM
#3
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I agree with Roberga. I had a guard unit put in my old 996 gt3 and in my 997 gt2 because the stock unit didn't make it through more than three track days. In each case the cost was a little less than $4,000 total parts and labor (about 2500 for the Guard unit). My local independent Porsche did both installs and did a great job.
02-13-2010, 06:18 PM
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I don't get it?? This post started as a nice technical discussion on diff's. Then turned into a sale pitch. Then a screw-job, $7500? hahahaha. Guard 50/80 diff, with the magical billet housing as mentioned above, WITH LABOR is a tad over $3000. That includes shipping...
Maybe I'm doing the math wrong? I'm confused?
Maybe I'm doing the math wrong? I'm confused?
02-15-2010, 10:05 AM
#7
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Thread Starter
Sorry to confuse, The $7500 is for a full billet unit, installed complete for race cars. That price included a significant amount of labor to remove the entire gearbox and replace the entire differential. The alternative for street and club racers uses YOUR differential with the guts from the billet unit and does not require trans removal. This saves around $4,000 so the net cost, installed from our shop is $3,000. It not a sales pitch, its saving club racers and DE guys from repairing their diff's with the same parts and the same thing happening. Or, even better, saving guys from spending the big bucks on overkill by intalling the full race unit. We have performed this differential mod on many 996 and 997's so many times, the customers asked if i would let people know.
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02-15-2010, 02:47 PM
#9
YearOne, - I am not sure but I seem to recall Matt was thinking of a working with a UK company as a distributor for GT Products, I am sure that if you gave him a call he would be able to help you.
02-16-2010, 03:51 PM
#10
Nordschleife Master
YearOne,
We've got a number of dealers in the UK or can work with you directly if you prefer. Feel free to contact me through PM or at my email that's listed in my profile.
As for what Mike is saying above, in case it's still not clear, a HUGE part of that $7000 number he's listing is R&R of the gearbox and setting up the ring and pinion. Some of you have been able to get your LSDs installed for significantly less labor but I think that's often the exception, not the rule. Many shops won't even attempt to set a ring and pinion if the gearbox is still in the car. Depending on the shop, that's anywhere from 6-8 hours of labor before the LSD install even starts. If you remove your own gearbox and take/ship it to a shop that price goes way down. I think he's also using the price of our motorsports LSD and not our club version. There's about a $500 price difference between the two models.
I think the service he's offering is a very cost effective solution to a problem that's quickly showing itself on the 997 GT3's that are making their way to the track. With the 996 version it was cheaper because Porsche gave those cars better ramp angles and locking percentages. All you had to do was throw in our discs, plates and pressure washers and be on your way. With the 997 they pushed it further towards the electronic babysitters and made the LSD looser and less effective. Almost everyone I've talked to doesn't like it when they take it to the track and turn the PSM off. That's where the GT ramps come in. This is why this service is going to cost you 997 guys more than on the early GT3's. Or if you are happy with the lower locking percentages and just want the LSD to work at it's original lockup then just don't change the ramps and basically cut the parts cost about in half.
We've got a number of dealers in the UK or can work with you directly if you prefer. Feel free to contact me through PM or at my email that's listed in my profile.
As for what Mike is saying above, in case it's still not clear, a HUGE part of that $7000 number he's listing is R&R of the gearbox and setting up the ring and pinion. Some of you have been able to get your LSDs installed for significantly less labor but I think that's often the exception, not the rule. Many shops won't even attempt to set a ring and pinion if the gearbox is still in the car. Depending on the shop, that's anywhere from 6-8 hours of labor before the LSD install even starts. If you remove your own gearbox and take/ship it to a shop that price goes way down. I think he's also using the price of our motorsports LSD and not our club version. There's about a $500 price difference between the two models.
I think the service he's offering is a very cost effective solution to a problem that's quickly showing itself on the 997 GT3's that are making their way to the track. With the 996 version it was cheaper because Porsche gave those cars better ramp angles and locking percentages. All you had to do was throw in our discs, plates and pressure washers and be on your way. With the 997 they pushed it further towards the electronic babysitters and made the LSD looser and less effective. Almost everyone I've talked to doesn't like it when they take it to the track and turn the PSM off. That's where the GT ramps come in. This is why this service is going to cost you 997 guys more than on the early GT3's. Or if you are happy with the lower locking percentages and just want the LSD to work at it's original lockup then just don't change the ramps and basically cut the parts cost about in half.
02-16-2010, 04:00 PM
#11
GT3 player par excellence
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Perhaps motorsport LSD cost more than clubsport LSD
I had my gearbox removed
shipped from ca to Copans when gas was $4/gal
Brian installed gurad LSD and 4.0 R&P. Either he didn't charged me or he's superman fast.
I had my gearbox removed
shipped from ca to Copans when gas was $4/gal
Brian installed gurad LSD and 4.0 R&P. Either he didn't charged me or he's superman fast.
02-16-2010, 08:43 PM
#13
GT3 player par excellence
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U r right
I think u can blind fold the guy and tie his hand behind his back and
he most likely still b the fastest gearbox magician out there.
I think u can blind fold the guy and tie his hand behind his back and
he most likely still b the fastest gearbox magician out there.
