Gretch

"I swear that the PSD light flashed when I put in the clutch doing that gear change on the sweeper at about 90 mph."


I've heard tell that little manuver can cost you some sheet metal........glad it worked out.

The PSM system in my 996 "saves my ***" on occasions when I have provided input that breeches the laws of physics ........

Flott Leben

Just on a side note: I drove (pretty spiritedly) a '93GTS through the streets of New York a few months back and noticed that the PSD light came on quite frequently as I took sharp turns from avenue to cross street while going over rough asphalt, potholes, etc. The car felt pretty darn stable. (The only thing that bothered me was that the RDK light went on almost as frequently! )

jpitman2

Down here in South Oz where the roads are damp quite often now, I find the LSD comes in quite often. Every time I take off into a turn that starts to unload the inside wheel, I think I can feel/hear the start of traction loss, and then a catch and we depart smoothly. If each of these produced some wheel spin if there was no LSD, a lot of heads would turn..(fine), and I would not get away so quickly (not fine).
jp 83 Euro S AT 48k

Cameron

Gretch,

It was part of the learning process for me. In my first session, I wasn't even carrying enough speed through the previous S turn to make that upshift before the next braking zone. After riding with my instructor between my first and second run, I picked up the line alot more. I observed him making this shift in his 996, being surprised that he would 'lift' at that point on the track. Now, the sweeper has flattened out a bit by this shift point, so it is not quite as agressive as it might sound. Still enough lateral to have the car (his as well as mine) do a bit of a wiggle, though.

To be honest, when I was driving home with the huge smile on my face reviewing the things that I had learned, this was one of the items that stuck in my mind. Accelerating out of the corner, or in the case of this sweeper, right through the corner. The limits of the car are much higher than I had thought and this part of the track kept coming to mind.

.....Cameron
'91 Euro GT

Flott Leben

So, what is the general consensus: LSD is better or worse than an open differential?

Is is worth the money to buy a used LSD and instal it?

SharkSkin

It's generally considered better to have LSD or PSD than an open diff. If for you the disadvantages are outweighed by the advantages and you have the $ to drop into it, why not?

Ron_H

Dave knows of what he speaks, as he seems to have a fetish for testing the limits of adhesion around on ramps. Don't ask how I know this.

Bill Ball

Whether you will really find any advantage with an LSD depends on what you expect to do. As I said, I bought one, was ready to pop it in when I decided I probably would never notice the difference, so what was the point in changing out the standard one that was doing fine. All I ever do in the car is open road racing (speeds up to 160, fast turns) and run around the local twisties. I'd rather spend the money on a dialed-in suspension. That difference I would notice easily.

SharkSkin

Hey, don't you make fun of my little on-ramp now... That was just a turnaround point for what we said was going to be a "little spin up the highway". Anytime you want to go on a little "testing the limits of adhesion" run let me know. Always good to have a passenger who won't leave pucker marks on the leather when I decide to experiment.

Dennis K

I've driven cars with PSD, LSD and open diffs on the street and at driver's ed days on the track.

FWIW, I really liked the PSD system. Some think it's inconsistent or throws a variable into the handling, but I always felt it was a safety net like ABS, where if you screwed up it tried to actively save you.

I upgraded my current car from a open diff to an LSD (I bought my LSD from Bill). Was it worth it? Well for track use, it is. When you laid on the power coming out of hairpins with an open diff, one wheel would start spinning and you could watch in the mirror as a single black line emanated from the back of your car. Until you lifted hard, the tire would just keeping spinnnnnning, which was kind of fun but slow. It made the car sound like it had a 1000 hp as it would go BWHAA-WHAA-WHAA-WHHAA down the straight. With LSD, you can stay on the power at corner exit and the wheelspin will subside by itself. For street use, I don't think I'd notice the difference that much. I guess it all depends how often you find yourself getting one-wheel spin exiting corners during your daily driving.

Example of LSD helping wheelspin (5 MB)
But it's not a cure-all for bad driving (5 MB)

Flott Leben

Thanks, guys.

Dennis, nice videos. The second one wasn't too bad.

I guess what I'm asking is basically: "Is the LSD a safety feature or a performance feature?" I've heard conflicting reports about cornering, on wet pavement, on ice, etc. Sorry to belabor the point but I'm considering investing in an LSD.

heinrich

Limited Slip Differential, aka Positraction, is 99% a performance feature. The safety is a side-effect, much as the design of any Porsche is 99% for performance, and safety is a side-effect of excellent engineering.

You might say that a locked diff would be 100% performance, but usually a locked diff would not only cause undue tyre wear, but also very lacklustre turning circle for esses and chicanes. That is, except on an oval track where you could lock the diff at a set ratio I suppose.

Jim bailey - 928 International

The regular limited slip is really for performance not "safety" and will in fact make it much easier to power oversteer on a wet slippery road and see the rear end go around the front end if too much right foot is applied . A slip can help keep you from getting stuck in snow but if there is enough snow to get stuck driving the 928 is probably a bad idea . If you currently experience wheel spin with the inside wheel when accerating and turning the slip will allow both rear wheels to spin if you push hard enough .

Ron_H

Dave:

You're on. The next BAR drive down past Hollister will be a good time. Keep watching the posts on the Yahoo site. Sooner or later someone will want to do it again. Only one mishap of which I am aware: a C4S totalled into a tree. A big "oops".

Don't worry. No one was making fun of the action; I found it "interesting".
and "informative", since I am so sedate a driver.

SharkSkin

No worries.