Question: Does the 2.5 RS come with a viscous limited slip differential on the rear axle. Can anyone confirm if this is true?

The RS has an open rear diff. You may install a limited slip or a viscous limited slip. At 165 hp the RS will tend to push more than it already does with the power on, although a limited slip is a blast in the rain.

There are three diffs, one for the front, located in the front portion of the trans case aft of the clutch, the center viscous diff at the end of the trans and the 'good ole' Hitachi R160 (Datsun 510-610 used the same one! starting in 68) in the back.

Question: I have a 97 Outback and I am interested in a viscous limited slip or Gleason "Torsen" rear diff. Anybody know where to get one?

Answer: The Subaru Viscous LSD is available from SPD Tuning Service. You need to disassemble your diff, and install your ring gear on this center section. Measure the backlash before you take it apart. You will need a press and a good set of pullers. I use a small oil bath oven to heat the ring gear prior to pressing it on, but it can be done without it. You should also be prepared to order a set of side shims, so you can get the back lash correct with the new center section. I have often seen that new shims are not required, but when you need 'em, you need 'em. A wet plate (classic Salisbury type) LDS R160 center is available from STi.

Many people are attracted to the Gleason-Torson worm and roller "slip locking" diffs. The Gleason will lock the rear diff when one side slips, and this is known in racing circles to make the car tend to push. Not a big problem with a high HP rear wheel drive car. It is a real issue in a 4wd car, as they tend to push with the power on to begin with. Not especially recommended.

I'd stick to an open diff until I saw tire smoke - and with only 165hp that will be a while. You'll have better handling, if a little less traction. With lots of horsepower, it would be a different issue.

I have driven 240hp 4wd cars with and without rear LSD. I'd say that the open diff car was easier to drive. The LSD caused understeer with the power on and with it went the ability to steer the car coming off of first and second gear asphalt corners. This will be particularly true with only a 15mm bar on the rear. Once the power is down, you'll have little steering left.

However, with the rear LSD it was a blast to use full power at intersections when making a left turn in the wet. Until the day some poor SOB tried to follow me in his 911. He looped it hard into center curb in front of god and everyone. If the curb had not been there he would have hit stopped cars. Ever since I've been very cautious about who is trying to follow me in the wet.

One reservation about not having a rear limited slip.. It is possible to get wheelspin off of corners. But this is usually cured by taking the corner faster...so that the wheel slip is the result of side forces first, and power second!

Question: Want kind of advantage do I get if I had three limited diff slips? One on the front, center, and rear?