The Race Line
01-23-2014, 07:35 PM
Hey there everyone,
I have been speaking with a couple of you here recently about some options for Limited Slip Differentials for the 818 build, and I thought I would share some information that may help some of you determine which direction to go in. There are essentially three different styles of differentials for the 818 or WRX gearbox.
1) open style differential which is the stock differential. This is essentially a one wheel drive differential. Not ideal for aggressive driving styles.
2) torque biased differentials. These would be like the Torsen or Modena or Quaiffe. These differentials are fairly good for the street, however they do not offer any lock-up on the deceleration side of the differential, only on the Acceleration side. It is also important to note that this style of differential, while indeed giving both wheels traction, will continually transfer power side to side, left wheel to right, giving the most power to the wheel that has the least amount of grip on the road. To put this more simply, if one wheel is on pavement, and the other on say dirt, then the differential will transfer a majority of it's power to the wheel on dirt, as it has less traction then the one on pavement. This style is a good option for street applications that are not too aggressively driven. This style of differential is not typically recommended for track applications. One other nice part of this style of differential is there is essentially no maintenance involved with these differentials, as they utilize worm gears instead of clutch plates, which can at times wear out.
3) salisbury style differentials, or plate type diffs. These differentials are true Limited Slip Differentials. Originally designed and developed by Porsche this style of differential has not changed substantially since its development. This differential has a couple of core parts that all work together to allow both wheels to maintain traction regardless of the surface they are on. These differentials come as either a 1 way, 1.5 way, and a 2 way.
* 1 way differentials have lock up only on the acceleration side of the differential, and no lock up on the deceleration side.
* 1.5 way differentials which is what most people will want to utilize, will give full lock up on the acceleration side and about 50% lock up on the deceleration side of the differential.
* 2 way differentials lock up equally on the acceleration side and deceleration side of the differential. While there are some drivers that like this setup, most find that the lock up on the deceleration side is too aggressive, and can cause instability in the rear-end, under hard breaking.
In terms of the differences between makes and models of the salisbury style differential, there are a couple. One will be the number of plates, the differential has internal to it. Another will be the type of plates used, and their configuration inside the differential. Many salisbury style differentials will have two plates that work together to form a clutch pack; one friction plate, and one plane plate which is usually smooth. These plates are held in place by two cupped plate washers. These belleville washers determine the amount of pre-load pressure that the clutch plates are constantly under. The more the pre-load the more breakaway torque is needed for the differential to release one wheel from the other. This is important as this will greatly effect the overall feel and operation of the differential. The more break away pressure there is the more the differential can cause the rear end to feel upset, or cause wheel hop around slower turns. These differentials, ones with more breakaway pressure will require more maintenance, as they are constantly under load and will wear quicker.
There is another way that a couple of companies have developed recently, to actuate the differential's lock rate and increase both plate number, and overall durability. Rather than utilize the belleville washers to control the rates of lock up initiated by the ramps, the ramps are counter sprung against each other, and it is the spring pressure that controls the rate of lockup, which makes this style of differential a bit more tune-able.
I am very happy to report that I can now offer the 818 community several options for both the standard 5 speed WRX gearbox (bug-eye 2001-2007 donor cars), as well as for both the 5 and 6 speed STI gearbox. I look forward to answering any questions that you might have as well as help more of you now with your builds. I hope that this information has been helpful, please feel free to give me a call with any questions or PM me so that I can respond to you right away.
Happy Building all,
Erik Johnson
The Race Line
(970) 344-7761 phone
I have been speaking with a couple of you here recently about some options for Limited Slip Differentials for the 818 build, and I thought I would share some information that may help some of you determine which direction to go in. There are essentially three different styles of differentials for the 818 or WRX gearbox.
1) open style differential which is the stock differential. This is essentially a one wheel drive differential. Not ideal for aggressive driving styles.
2) torque biased differentials. These would be like the Torsen or Modena or Quaiffe. These differentials are fairly good for the street, however they do not offer any lock-up on the deceleration side of the differential, only on the Acceleration side. It is also important to note that this style of differential, while indeed giving both wheels traction, will continually transfer power side to side, left wheel to right, giving the most power to the wheel that has the least amount of grip on the road. To put this more simply, if one wheel is on pavement, and the other on say dirt, then the differential will transfer a majority of it's power to the wheel on dirt, as it has less traction then the one on pavement. This style is a good option for street applications that are not too aggressively driven. This style of differential is not typically recommended for track applications. One other nice part of this style of differential is there is essentially no maintenance involved with these differentials, as they utilize worm gears instead of clutch plates, which can at times wear out.
3) salisbury style differentials, or plate type diffs. These differentials are true Limited Slip Differentials. Originally designed and developed by Porsche this style of differential has not changed substantially since its development. This differential has a couple of core parts that all work together to allow both wheels to maintain traction regardless of the surface they are on. These differentials come as either a 1 way, 1.5 way, and a 2 way.
* 1 way differentials have lock up only on the acceleration side of the differential, and no lock up on the deceleration side.
* 1.5 way differentials which is what most people will want to utilize, will give full lock up on the acceleration side and about 50% lock up on the deceleration side of the differential.
* 2 way differentials lock up equally on the acceleration side and deceleration side of the differential. While there are some drivers that like this setup, most find that the lock up on the deceleration side is too aggressive, and can cause instability in the rear-end, under hard breaking.
In terms of the differences between makes and models of the salisbury style differential, there are a couple. One will be the number of plates, the differential has internal to it. Another will be the type of plates used, and their configuration inside the differential. Many salisbury style differentials will have two plates that work together to form a clutch pack; one friction plate, and one plane plate which is usually smooth. These plates are held in place by two cupped plate washers. These belleville washers determine the amount of pre-load pressure that the clutch plates are constantly under. The more the pre-load the more breakaway torque is needed for the differential to release one wheel from the other. This is important as this will greatly effect the overall feel and operation of the differential. The more break away pressure there is the more the differential can cause the rear end to feel upset, or cause wheel hop around slower turns. These differentials, ones with more breakaway pressure will require more maintenance, as they are constantly under load and will wear quicker.
There is another way that a couple of companies have developed recently, to actuate the differential's lock rate and increase both plate number, and overall durability. Rather than utilize the belleville washers to control the rates of lock up initiated by the ramps, the ramps are counter sprung against each other, and it is the spring pressure that controls the rate of lockup, which makes this style of differential a bit more tune-able.
I am very happy to report that I can now offer the 818 community several options for both the standard 5 speed WRX gearbox (bug-eye 2001-2007 donor cars), as well as for both the 5 and 6 speed STI gearbox. I look forward to answering any questions that you might have as well as help more of you now with your builds. I hope that this information has been helpful, please feel free to give me a call with any questions or PM me so that I can respond to you right away.
Happy Building all,
Erik Johnson
The Race Line
(970) 344-7761 phone