Pelican Parts Forums - Dumb question: Was lsd an option ??

I drove an N/A 944 for more than 3 years with a factory M220 option LSD in it. Barely noticed it. Then I bought a 911 with an open diff and drove it on the street for about 12,000 miles.

Then I spent some money on the 911, including another gearbox, which was fitted with an aftermarket plate-type 40/65 limited slip diff (generally considered ideal for street and limited track). This was set to the maximum rating - about 70 ft/lbs, IIRC.

The difference in the "feel" of the 911 under trailing throttle from speeds above 40 MPH - was very marked with the LSD, and surprised me more than somewhat. Far more stable. The improvement in stability and traction when cornering was more expected - and also a huge difference.

The minor added (and momentary) "push" on turning in was easy to get used to. Don't even notice it now.

There is also some imparted push when the unit locks up when the car is accelerating. An LSD can also make low-grip conditions much less drama if you overcome available traction. At least you stay in your own lane.

I was completely sold within about a week, and I can't actually imagine how it could fail to improve any 911 - probably why it was offered as an option on every model Porsche built since the 356. I've got about 12,000 miles since the LSD was fitted, and I think it's the best single improvement I've made to the car.

I drive the car on the street all the time, all conditions, and I find that a plate-style LSD is only really noticeable at low speeds in two circumstances: via a little extra initial mechanical slop when reversing out of parking spaces (feel the plates engaging in the other direction) or when pulling away in low-grip conditions like on grit/gravel (both wheels scrunch). The 1/8 second "push" on turn-in doesn't really happen at 5 MPH, and I'm already mentally compensating for that anyway.

For higher speeds/transitions, the LSD is very noticeable from the increased stability - the rear feels totally "planted". Same tires, same suspension, same alignment.

And there is no down side that I can see, other than cost. For track use, experienced folks apparently generally report a second or so off their lap time after fitting an LSD in what is otherwise the same car. Partly because they're getting power to the wheel that needs to go faster (instead of spinning the light wheel), and partly because the car is cornering better and more stable.

Hayden (of WEVO) also cites an LSD as a factor helping to keep 915's together in high-power (350+ ft/lbs) applications. It's all good.

The later (84-up) factory LSD's were pretty anemic @ 25 ft/lbs (the so-called "snow-only" LSDs). Current aftermarket LSD's are available in a variety of options, the Velocity article <a href="http://www.guardtransmission.com/velocity.htm">here</a> is very informative.

Is it sought after? They are an advantage, but they have a finite lifetime before they require servicing - and many older ones haven't been - and the original factory ones aren't especially interesting (if they're worn-out, weak by design or both) - and the aftermarket ones can be so much better.

I think it'd likely make a car more desirable to have a functioning LSD fitted, but not necessarily something you'd want to pay extra for. Although the going rate for a used LSD is around $1000, I believe... (Paul Guard's GT diffs are very well regarded, and sell new for more than that if you can get one - they seem to all get snapped up whenever he makes any).

For AutoX, a Torque Biasing diff is apparently better than a plate-type anyway.