rwilliamtaylor

I've begun to explore the limits of my new 996TT X50 and have a question about PSM. Under full accelration in 1st and 2nd gear it feels like I hit the rev limiter at about 4500 RPM. Is this the traction control? I don't get a PSM light onthe dash? When I exit a corner hard and the car oversteers I do get the PSM light flashing on. I also get a bit of slip angle before PSM intervenes. I'm used to the BMW DSC which didn't allow any slip.

Is this how PSM works? The user manual is pretty vague onthe subject.

Carnerd

Generally PSM will let you play/slip a little before kicking in. Although every time it does intervene you should get a PSM light. What happens when you turn PSM off and go full out in first and second? Do you still hit something that feels like a rev limiter at 4500?

Chuck Jones

Sounds like you have a vacuum leak....you shouldn't get any drop in acceleration till you hit 6800 rpm when the rev limiter kicks in. I've only invoked the traction control two times....both times in the rain when I was making a tight righ hand turn and the rear end broke loose. The correction was actually very subtle...this car doesn't scream "YOU DUMB ****" when the traction control kicks in....it just very subtly corrects the error and whispers to you with a light on the dash that stays on only when the correction is being made. Of course the subtleness is directly related to how badly you've screwed up. If I had gone sideways, the correction wouldnt' be so subtle. What you're experiencing at 4800 rpm doesn't sound right.

killerbee

I have experienced psm regularly in ax, couple of times messing around on an intentionally water soaked skid pad and on the track. In all instances significant wheel slippage has accompanied its activation. The track experience related to a excessive set of tire pressures that contributed to poor traction and the resulting slippage under WOT. I'd suggest that you check your tire pressures as a starting point.

As far as what it feels like....A significant drop in power as one of the things that is done is to close the throttle and pull timing. However, when it happens I always see the PSM light flash.

BTW I am sure this is a gross simplification.

1AS

I activate the PSM all the time, as I drive in snow. You definitely feel the power cut off, and the car will brake the appropriate wheel. If you have the radio on, you will also hear static. It isn't really subtle at all. We have a new Audi tt (2.0 turbo) for my 18 year old son, and in that one, it is very hard to feel the psm kick on. You need to watch the light. In the Porsche, you don't need to watch the dash display, you will definitely feel it.

To be accurate, the PSM allows some rotation under braking, but very little on acceleration. On a wet track, the car will have pure understeer on acceleration out of a corner. To do anything with the car on a wet track, you need to turn it off. Same on a dry track, but the speed loss is not as apparant. AS

Beej

FYI here is a link to a great article that explains exactly what the Porsche PSM system does from a drivers perspective in a track situation:

http://www.deter.com/porsche/PSM.txt

Cheers and Merry Christmas to all!

Beej

rwilliamtaylor

Beej,

Great article,explains why it doesn't behave like my M3.

I tried full acceleration with PSM off and no loss of power through 1st and second, although the car got a bit loose in first, but nothing too dramatic.

I adjusted tire pressure on the Toyo proxes 315/25/19 and 245/30/19s to 40psi rear and 36psi front (cold) and tried full tilt with PSM on and it pulled right to red line.

I guess it's working as intended. Thanks for the advice.

1AS

Nice link, but a little over-enthusiastic. You can get the car to rotate under braking, but not with throttle. Once you hit the throttle, the rotation ends. I would hazard a guess that someone who really knows the system (like the test engineers) can steer out enough to allow the car to take uninhibited throttle, but in the laps I've run, I feel the engine cut out. If anyone has a different experience, I'd love to hear it. AS