Manifold

So the 991 GT3 has a rather comfortable ride on the road in the softer damping setting, and is even fairly comfortable in the stiffer setting. Yet on the track, the suspension is plenty stiff and the corresponding performance level is very high. Given that the spring rates are fixed, the ability of the suspension to work so well in all these diverse situations has to come down to the shocks, and I'm suspecting that some rather sophisticated algorithms are being using to continuously and very quickly vary the damping at each corner in real time.

Anyone have any details on how the PASM in this car really works? I don't see much on the website.

I'd also be interested in knowing the replacement cost for the shocks, and I wonder what the durability of the shocks will be under heavy track use. Perhaps data from the 997 GT3 shock will be relevant there. With my 997.1 C2S, the PASM shocks seemed to wear out within 40 or 50 track days, but the car was 7 years old when I started tracking it (street only during those 7 years).

24Chromium

I suggest you hop on over to the 997 GT board and read up on TPC's DSC offering. Lots of technical info and high praise from those who have installed it.

gled

There is no Service Information for PASM for 991GT3. That means most of the system is carried over from previous models. The new Boxter Service Info states: "PASM is a shock absorber system for active and continuous damper control at the front and rear axle. PASM has been enhanced to optimize the control and the resulting improvement of the driving comfort and driving dynamics. In contrast to previous models, there are four additional angle sensors on the front and rear axle and another front left body acceleration sensor for even more precise control. The damping force for each wheel is individually regulated, depending on driving style and driving conditions. The result is significantly enhanced comfort in both programs." The GT3 has to be at least this if not more. Gled

Macca

The 991 GT3 chassis stiffness must in part be due to this chameleon feat of being brilliant on road and track. I dont have prior ownership experience of 997 gen GT3 but compared to my old 996 GT3 this is one very stiff chassis indeed (lifts a wheel every time I exit my gas station drive way apron at an angle!).

PC Valkyrie

Porsche Active Suspension Management (PASM) is obviously standard on our GT3's.

The PASM damper (shock) has a control wire connected to the head of the unit. This wire connects the damper to a central control unit that is connected to sensors that measure steering input, body roll, suspension bump and acceleration. If the control unit determines that the car is being driven in a sporty fashion, it will decrease amount of oil flow in the damper via a bypass valve, making the damper/shock stiffer. This all happens in real time, so it adapts to the type of driving you are doing.

Spyerx

Regarding durability I had a front go out on my 997. Electronics went wacky. This was at 29k miles and minimal track. Shock was 800 at the time. For 1. I opted for ohlins.

isv

A couple of people that I know of who are really good drivers have mentioned that PASM can potentially quite badly affect the ability to load the front axle while trail braking on track for the 7 GT3 generation. Just wondering, does that happen still for the 991 GT3 for those who have tracked it?

Manifold

Main thing I'm wondering about is the increments of adjustment in damping rates for each shock, and how frequently the rates are being varied.

In other words, at one extreme, it could be a large spectrum of rates being adjusted microsecond to microsecond based on many inputs from many sensors, all done independently for each shock. At the other extreme, there could just be say ~3 damping rates to choose from, with the selection made by how aggressively the car is being driven overall, such that the damping rates are hardly or never varied within a track session, and are always the same across all four shocks.

And to reiterate, I ask the question because, since the ride can be comfy, that means that the spring rates aren't particularly high, so a lot is being accomplished by varying damping rates. From my (ongoing) experience with trying to dial in the suspension of a car with non-PASM 1-way adjustable Ohlins shocks - playing with spring rates, valving, and selection of damping rates (adjusting 'clicks') - making a suspension work well on both road and track by adjusting only damping isn't easy.

Macca

Relax Manifold Relax. There is no definitive answer to your question I am aware of and it will probably take some time before someone reverse engineers the system to find one......but in the meantime rest assured that whatever alchemy is at play works very well indeed. As a coil-over man on an older platform (triple brace, half cage, mono *****, camber plates, full spherical rear suspension with sold mounts RS uprights, rebushed A arms, RS front tire rods, fully adjustable RS sway bars etc) I can attest that after spending 15-20K on upgrades, geo and dialling in over 4-5 years on the 933 the tech in the GT3 chassis just made me realise the magic that is A). chassis stiffness and B) immediate electronic control of strut compression and rebound. Im not sure they will even need springs for much longer - probably use magnets instead LOL! The fact is on the 993 even dialling right back my shocks, softening up my sway bars to the softest settings and replacing all the solid mounts and heim joints I now have with lots and lots of really soft rubber my 993 would never come close to being as compliant on the road as my GT3....the 993 still is very fast in the corners however. Infact if it had 200kg less and 120 bhp more it may even keep the 991 GT3 honest on the shorter tighter courses, but then it would be a really uncompromising race car and I couldnt have done the 4000 miles of touring with my wife on two continents ;-)!

Manifold

Macca, chill out, it's a technical question about how the car works, same category as other technical questions. Porsche knows how it works, and we have contacts within Porsche, so answers can be found without reverse engineering.

montoya

Sounds like they are still not using the magnetic fluid shocks like the corvette and BMW use. Too bad that was magic on my old m3.

kencollinsjr

Manifold: Please don't get sassy w/ our good friend Macca...

Manifold

Lol, I don't think Macca is that fragile!

Macca

All good folks :-)
I confess even I get out of line sometimes lol!

Mike in CA

For those interested, here is a description in general of how PASM works:

Unlike conventional dampers, the PASM map-controlled damper also has an electrically actuated hydraulic bypass valve. The damping effect is provided by the oil in the damper
flowing through a piston valve when the vehicle moves. The smaller the valve cross section, the harder the damping.
With the PASM damper, the oil can flow through a bypass valve, as well as
through a fixed valve in the main piston. The flow can be increased or reduced by opening and closing the valve via a slide,
producing continuous adjustment of the damper force. In the event of a system failure, the valve automatically closes. PASM is then in the hardest damper setting
and thus the safest mode from a driving dynamics point of view (fail-safe principle).

Lane-change module
The damper forces at both axles are immediately increased in response to
rapid steering movements, for example sudden evasive manoeuvres.
This reduces body tilt and instability, thereby significantly improving vehicle
control even in extreme situations.

Vertical-control module
In the Normal programme, the damper force is increased as soon as the
vertical movement of the body, for example when driving over uneven surfaces, rises over a specific threshold value.
This prevents body instability and therefore woolly driving behaviour.
In the Sport programme, the damping is slightly reduced automatically to
improve contact between the road and the wheels as body movements
increase. This also results in a noticeable increase in comfort.

Lateral-acceleration module
If specific, speed-dependent thresholds for lateral acceleration are exceeded
when cornering in the Normal programme, the damper force is increased by
different, defined amounts for each side of the vehicle. This prevents vehicle
instability and significantly increases driving precision. In the event of large vertical movements and high lateral acceleration coinciding,
the higher of the vertical-control and lateral-acceleration damping values is set. This happens if, for example, the damping in the
Sport programme was previously decreased by the vertical-control module.

Brake module
PASM switches to harder damping at the start of a braking operation to reduce vehicle nose-dive when braking. This way, higher brake forces can be
transmitted to the road faster. It switches back to a softer setting (this setting is different for the front and rear axle) after a specific amount of time.
The result is improved road contact, and thus a shorter braking distance, particularly when braking on uneven surfaces.

Load-change module
The damper characteristics for the front and rear axle are individually switched when accelerating heavily, releasing the throttle or changing lanes. In Normal mode,
the dampers are briefly switched to a harder damping setting in these driving conditions. This avoids excessive lifting or diving at the front of the vehicle (“pitching”).
In Sport mode, a softer damper characteristic is briefly selected if necessary to improve traction when accelerating, particularly on uneven surfaces.

Components
The PASM system comprises the following components:
• Four dampers with continuously adjustable damping force (each with one
bypass valve)
• PASM control module
• Two acceleration sensors for detecting vertical movement of the body
(one at the damper dome at the front right and one at the rear left).
Further signals such as lateral acceleration, steering angle, travel speed,
brake pressure, engine torque, etc. are read in via the CAN bus.

The system measures body movements via one acceleration sensor on each
axle (front and rear). Values such as lateral acceleration, steering wheel angle, vehicle speed and information on possible braking operations are provided by the PSM via the CAN bus.
Engine rpm and torque values are provided by the Motronic via the CAN bus.