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Discussion Starter · #1 ·
just want to learn a little more about how the 02-03 RS's awd system works...


the 02-03 RS doesn't have a limited slip diff. in front or back right?

Under no slip conditions, is power split equally to the back & front, or only the front?

When slip's detected (for an example we'll say in front), is 'all' the power sent to the back, or is just a percentage sent to the back?


thanks everyone!...
 

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Yup, the '02/'03 RSs don't have a rear lsd.

For a manual trans, power split is 50/50
most auto trans are nominally 90/10 (including the RSs) but some of the newer Subarus with VDC i think are different.

As I understand it, only a percentage can be sent back since the lsd only serves to turn the front and rear ends at the same speed. So you have to be putting power there in the first place before it will slip. Then the lsd starts working.
 

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the way a viscous coupling center diff works is that when one driveshaft spins faster (i.e. the wheels on that end are slipping) this goo inside it gets very thick (hence the name viscous). this produces more resistance on the slipping driveshaft and engine torque, like water, seeks the path of least resistence. since there is more friction being applied to the slipping driveshaft, the engine torque heads to the other, non-slipping one (in your example the rear). how much torque is transfered is proportional to the amount of slip, to some degree. the V-LSD cannot lock, so it can't send all the torque to one driveshaft or the other, like the 22b can. so your limited in the amount of torque that's transfered both by the amount of slip and the amount of transfer that the center diff is capable of. now i know, you're thinking "how much is the stock diff capable of" and i can't tell you exactly. perhaps someone else is more knowledgable.
 

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Discussion Starter · #4 ·
...thanks guys!

ok, now for a question I've always wondered about: since the 22B can transfer all the power to the front or back; could someone in theory put a smaller rim/tire combo in front (let's sat 15", assume it would clear the brakes etc); and the oem 17" setup on back...

...the center diff. would think the front was always slipping, transfering 100% of the power to the back; and the car would effectively be rwd? not to mention really funny looking...

then again, the B's so advanced they probably have a switch to instantly change it to rwd like skylines or something!
 

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Discussion Starter · #6 ·
thanks for the info... I'm assuming there's no aftermarket center locking diff. for the RS right?

someone else on the 'I' board said the sti can switch power to the front or rear to the tune of 65%... It's prob. not too much different for the rs/wrx here in the us...
 

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I'm assuming there's no aftermarket center locking diff. for the RS right?
are you kidding, this is capitalism, anything can be had for the right price :)


someone else on the 'I' board said the sti can switch power to the front or rear to the tune of 65%... It's prob. not too much different for the rs/wrx here in the us...
it is true. the US-spec STi has what is called a Driver Controlled Center Differential (DCCD) which is reserved for the Type RA models in Japan (thank you subaru :D ). your assessment is both correct and missing the point. the DCCD has two modes. the first is just like the viscous LSD on the WRX and RS, though mechanically actuated. it sits happy at a 50/50 torque split until things go ary, and then it automatically varies the amount of torque front vs. rear depending on slip conditions. however, the driver can also put it into a "locked" mode in which the driver pre-sets the torque split, anywhere from 50/50 to 35/65. this is within the range of adjustment that the diff will make automatically but in this mode the diff is locked into that split. this means that if you have it set 50/50 and slip occurs, it won't suffle the torque around. this is mostly nice for dry tarmac where you can create a RWD bais to help alleviate some of the inherent turn in understeer in AWD. the surtrac front LSD in the STi also helps with this.
 

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this dccd diff you talk about is it just available in the japan model? (if so how much do they cost and where can you find them)
and what's the power split on the manual 98-01 2.5rs ? And then what about the new Wrx's like 02-present. Excluding STi. I'm interseted in buying a 2.5rs or wrx. But i want wich everyone has the most munipulation room as far as trany/drivetrain for either doing rally or auto cross. :confused:
 

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i'm sorry if i wasn't clear about the DCCD. it is available in Japan on basically the factory race cars AND the US-spec STi. subaru was very very kind to us indeed. you can buy them from a variety of sources, but they cost a couple grand and may (i'm not sure) require the 6 speed as well, which will be another ~$8k.

the center diff in all the RS's and WRX are the same unit (for a manual tranny). its a 50/50 split, but i don't know the variablity limits. the advantage of the DCCD is that you can set it to permenantly have a rear wheel bias, which is better for auto-x and track events.
 

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Discussion Starter · #10 ·
great info, thanks...


o man, I'd pay $1500+ to have the ability to flick a switch & go into rwd only. nothing like being able to drive to a drift competition in the snow, get some good drifts going w/ the rwd mode, and drive back w/ wonderful awd...
 
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