I was wondering if anybody could remind me on what exactly an LSD does. I understand my 2002 RS doesn't have one. Could a WRX LSD be installed in my RS?? What would this do for me??

go to www.howstuffworks.com and look in the automotive section... they explain limited-slip differentials.

the north american WRX has the same type of rear LSD your RS does, a viscous coupling (it might be a bit larger though).

if you're still curious, use the search feature against the turbo powertrain forum (or maybe archive)-- it's been covered there a few times.

LSD (Limited Slip Differential) comes in 00/01 RS and 02 WRX. It limits the slip between the right wheel and the left wheel.

For example, in your 02 RS, you have an open rear differential. Suppose you have enough power to spin the wheels, only one rear wheel and one front wheel would spin. If you had a rear LSD, both rear wheels (and one front wheel) would spin.

You are correct that your 2002 2.5RS does not have a LSD rear diff., and yes, you can simply trade one from a WRX IF the WRX has the same final-drive ratio in the rear diff.

If you have a Sedan w/ M/T or a wagon w/ A/T you have a 4.11 diff., you could use a rear diff from a A/T WRX or 2000-2001 M/T 2.5RS. If you have Sedan w/ A/T you have a 4.44 diff. and could use a rear diff from a 2000-2001 A/T 2.5 RS.

You know, just the opposit of what Subaru tells you. If you don't have the LSD like me in my '98, it's "From the wheels that grip to the wheels that slip". I have no idea how Subaru came up with their slogan since the opposite is true. They should have to give us all front and rear LSD's just for blatently lying to us in their advertising.

Even with the LSD it won't transfer power from the slipping wheel to the gripping wheel. It'll just lock them together when the oil heats up inside the diff.

I think the ad campaign speaks of the auto tranny's ability to send power fore/aft, but I'm not sure.

The only true wheels that slip to wheels that grip vehicle out there that I know of is the '99+ Grand Cherokee with Quadra Drive... gerotor pumps front, rear, and center transfer torque to the wheel that grips. Sorta the same principle as the LSD, but instead of locking together somehow it sends it all the other way.