Well, that's what I thought... Got my 2005 car for a few months now and always thought that PASM had just two settings: normal (soft) and sport (firm) which just stayed either soft or firm for the entire ride. But it looks like I was wrong and the PASM module actually dynamically modifies the damping force in each mode, based on rapid acceleration, braking, rapid steering movenents, driving over uneven surfaces etc. I didn't know that. I thought you needed the DSC module for that. Now it seems to me that the OEM PASM module is also actively changing the damping forces, based on the CAN bus data. Maybe the DSC module just does a better job in trying to achieve the same thing (helped by an extra accelerometer in the 997.1 cars)?

Here's a direct copy-paste from the 997 2005 technical manual from Porsche:

Porsche Active Suspension Management (PASM)
For the first time in the 911 series, the new 911 Carrera S is offered with a
chassis that has actively adjustable dampers. The PASM is standard equipment
for the 911 Carrera S. In comparison with the standard chassis, the vehicle with
the PASM chassis lies 10 mm lower.
The newly developed, variable damping system “Porsche Active Suspension
Management” helps to do justice to the demands for a modern chassis.
The aim was to maintain the high comfort level of the standard chassis while
increasing performance at the same time.

The driver can choose between two programmes: “Normal” and “Sport”, both
are selected via a button on the centre console.
The function light in the button comes on with the Sport setting. At the same
time a damper icon appears in the instrument cluster display together with the
text “PASM Sport”. When the normal programme is activated, the damper icon
appears accompanied by the text “PASM Normal”. The text and icon remain
visible for 4 seconds and then disappear.
PASM combines two chassis rolled into one: One with equal measures of
sportiness and comfort and one entirely dedicated to sportiness and the race
circuit.
Normal mode (the basic setting when the vehicle starts) on the one hand
provides the same excellent comfort as the standard chassis, on the other
hand, the chassis approximates the sportiness of the sports chassis when
regulative interventions are made with active PASM. In conjunction with specially
developed software modules, the PASM ensures excellent performance and
even greater driving safety in extreme situations.

Operating principles of PASM
PASM selects the required damper hardness for each individual wheel from a
precisely co-ordinated map in both the Normal and the Sport programme.
The possible damper settings range from comfortable to decidedly sporty.
Both programmes, which overlap slightly in some areas, are additionally
superimposed with five special software modules to provide the optimum
damper settings for every driving condition.
The system automatically selects the appropriate damper hardness based on
the PASM programme selected and the driving condition identified.
The Normal programme offers comfortable settings with low damper forces.
Special control algorithms in the PASM software modules enable the chassis to
offer greater active driving safety in extreme driving situations, even with the
Normal programme. To increase driving safety at higher speeds, the dampers
are automatically switched to a harder damper setting as speed increases.
The dampers switch to a hard characteristic when Sport mode is activated.
This offers superior agility and excellent steering precision on uneven surfaces.
If the system detects an uneven driving surface in Sport mode, it immediately
switches to a softer characteristic to improve contact with the road surface.
PASM selects the optimum damper setting for this softer characteristic from
the Sport map.

Since extremely hard damping is not always the ideal solution in every driving
situation (depending on the driving surface, the vehicle may start to bounce or
shift), the intentional overlap between the Normal and Sport maps allows a
noticeably soft setting to be selected if necessary. The customer gets an
“active sports chassis” which automatically responds to the actual road surface
and switches from a hard, sporty damping setting to a comfortable range as
necessary. PASM switches back to the original characteristic as soon as the
road surface is smooth enough.
The following is a detailed description of the five software modules overlapping
Normal and Sport mode.

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.
• One button for selecting the programme (Normal or Sport)
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.

Acceleration sensor
The acceleration sensors are attached to the front right and rear left spring
strut domes, respectively.
The arrangement allows lifting, pitching and rolling movements of the body to
be measured.


I thought I might as well post this, as there might be other people that didn't know this yet.

 

It is called PASM, Porsche Active Suspension Management :-)

So.... no, never thought it was passive.

 

True but I must say I never noticed the 'active' part being active, nor reading these details.

So why would the DSC box be this much better, if it's actually trying to achieve the same thing, based on the same CAN bus input? Just better software, mappings and/or processing-power?

 

the dsc box uses a 3d accelerometer as input, rather than the 2d one that came with the 997.1. This gives it a lot more programming possibilities.

 

2009 C2S 185K miles

Yes, of course. The DSC is all about the mapping. You are assuming that Porsche fully implemented the possibilities of their own system. They did not. I don't know why, maybe it was part of their model planning... slowly improve the car? Or maybe they just didn't have the time?

Given the research I did a while ago, the Porsche system is pretty dumb despite the capabilities. It simply has a stiffening algorithm that is linear. The faster you go, the stiffer the shock. Linear. And, all four shocks are treated the exact same. For SPORT, the line is just moved up but even has the same slope. The DSC does a whole bunch of stuff differently including: Using other inputs other than speed, treating each shock differently to compensate for turning/accelerating/stopping, and using G-force in a 360 range to change each of your four shocks differently. And, DSC gave you software to tweak the maps as you desire. DSC did what Porsche never did. Shocking actually.

Peace
Bruce in Philly (now Atlanta)

 

Hi Bruce, you might be right that Porsche never fully implemented the capabilities of their own system, but from the text I copy-pasted above, it seems that they were already using a lot more inputs than just speed for 2005 PASM:

• speed
• vertical movement (uneven surfaces)
• rapid steering movements
• speed-dependent thresholds for lateral acceleration
• start of braking operation
• load-change (accelerating heavily, releasing the throttle or changing lanes)

Besides that, it's also saying: "PASM selects the required damper hardness for each individual wheel from a precisely co-ordinated map in both the Normal and the Sport programme."

Don't know if it really does what they say, but it sounds like they were already on the right track, not taking the quality of their mappings into account.

 

I stand corrected... but a bit confused. I am trying to find the Porsche publication that showed the PASM graphs... if I find it, I will post it. Here is the Porsche documentation I have for PASM in the .2 cars (I am not sure if this was from an official Porsche publication.. I don't know its provenance):My experience with my 2009 S was that I was never happy with the ride and handling. It was the biggest disappointment. My Boxster S handled way better... more composed.. more predictable... everything. I chose the DSC due to my dissatisfaction and not any desire to tweak the car. The DSC did just a better job.

BTW, could you forward the source of that document to me? I never saw that. I have what I thought was a complete library of Porsche stuff including the Technik docs for .2 and just don't have that in my library.

Peace
Bruce in Philly (now Atlanta)

 

Maybe this summarizes it best. Although I don't own the DSC controller yet, I was surprised to read that both modules basically use a lot of, or exactly, the same inputs (helped by an accelerometer for the .1 cars), and both do dynamic adjustments to all 4 corners individually. But one (DSC) probably does a better job than the other, based on the first hand user experiences that I read.

Here's the document for the 997.1 2005 : https://we.tl/t-ti45SgivGX

 

To me, the real beauty of DSC is the owners ability to customize the software and values so the car dynamically behaves exactly the way the owner wants it to for softness, firming rate, etc

Even is the stock PASM controller hss some adaptive capability, it just seems to be not good at doing it.

 

2009 C2S 185K miles

Quick observation: The more modern the suspension system (i.e., better), the more refined. What is refined? Smooth and comfortable while still performing like a track car... like it is on rails. Holding the road. Not bouncing or shifting direction on bumps. Still communicating what is going on to the driver.

The DSC provides the refinement that Porsche did not... and should have.

Peace
Bruce in Philly (now Atlanta)

 

Everything I've read implies that the OEM system is single channel while the DSC is for channel (dealing with each shock as its own entity). When I instalation the DSC I immediately noticed less squat on acceleration and less dive on deceleration.

Additionally, starting at a stop sign while turning kept the rear end stable rather than shifting to the outside rear tire. Before DSC the car would slide and require sensitive throttle control. With DSC I could supply significantly more power.

As for the OEM system, I've never cared for any system that adjusts to my driving style. Suddenly, with adaptation, the system starts to behave differently ... How can I count on the car being predictable? Technically, depending on how you drive, Comfort could become more sporty than Sport. With DSC I can count on the car being the same throughout a spirited drive.

 

This never occurred to me but I'm glad you posted it. Getting smart on Black Friday!

 

Great thread.

This is info I copied and pasted from Rennlist while researching the DSC box pre-purchase.

For all I know, Bruce, you might have written some of the comments.

I did attribute Tom’s comments, which does add some authority to the info.



“TPC Racing DSC PASM Control Box:

Review:
During my canyon driving, I didn't like how the stock suspension handled road imperfections, especially in the corners. I felt the car was getting unsettled. So, I decided to give the DSC Sport solution a try. It works by using the vehicle's sensor data to actively adjust the dampening.

Performance: Before testing the module, I did a few runs down one of my favorite canyon roads with both PASM set to normal and sport to get a baseline. Both mods performed well, however, I could feel some body roll and push towards the rear end during sharp switchbacks.

With the DSC module set to normal, I was extremely shocked with how the vehicle handled. In the first turn, turn-in was much sharper. It felt like the front dampers softened to help the nose rotate. It really felt like the car had torque vectoring. The car also was much more composed in the sharp switchbacks.

In DSC Sport mode, the suspension was noticeably firmer. Turn-in felt more similar to the stock PASM module, but body roll and weight transfer was noticeably better. Overall Sport mode felt great, but normal mode felt perfect for the particular road I was on.

Comfort: Comfort improvement was night and day. The car felt so much more refined. In normal driving, it soaked up road imperfections nicely. In the bumpy corners, the chassis never felt unsettled and the tires maintained constant contact with the pavement. The vehicle just felt more surefooted, which improved my confidence.

Installation: This so far is my favorite suspension mod because it's so easy to install. Just unclip your stock PASM control unit under the glovebox and replace it with the DSC module. Once I located the stock PASM unit and the retaining clip, it took me less than 1 minute to swap it out.

Overall: At $1,200, the DSC Sport module is on the pricey end, but cheap compared to other suspension mods. I love this mod because it doesn't make the car feel aftermarket, improves handling drastically, and while making the suspension more refined. It simply does a much better job than the stock unit at actively controlling the dampers to give you comfort and performance. You can even tune the maps."

Company founder response:

“Your description of the stock damping characteristics is spot on. The "float" is chassis oscillation at different frequencies from going over short duration bumps and from longer duration/highway speed road pitches, which can typically be prevented by adding rebound damping force.

The "bam" is result of too much compression damping at or before the peak of a bump. The theme is too much compression and not enough rebound.

DSC will change all this. With DSC, the damping commands to the PASM shocks are actively changing for the driving conditions and to the drivers inputs at a rate of every 100 millisecond = .1 second (every 6 millisecond with Tractive shocks). For reference, the average eye blink duration is 300-400 millisecond.

And don't forget guys, with the purchase of DSC you not only get the sum of the product you get life tie support on DSC software tuning should you want to make any custom changes to your DSC.

The stock 997.2 GTS (PASM) and with SPASM (I030 option code) do have more rebound than other stock 997 configs. So they do have less float when driving leisurely but their damping commands aren't actively changing to the level of DSC. For these cars chassis stability, traction, and comfort are also improved with DSC. There are extremely positive reviews of DSC users on GTS/SPASM car here on Rennlist."


From the 991 RL forum:

From Tom @ TPC:

"The DSC controller actively commands the dampers to the driver's input (steering, braking, accelerating), so yes, it can be softer than a 991 base when the car is cruising at steady speed with no additional activity from the driver.
As the driver's input activities increase, DSC commands the dampers to stiffen to counter the amount of load in real time. With load, DSC commands the damping force to be as stiff or stiffer than GT3.
Since DSC commands to the dampers are dynamic, it is not a fair comparison to simply say it is softer or stiffer, because it is both depending on the real time conditions.
One of the many features of DSC is that the "minimum" damping value in each mode (Normal mode and Sport mode) can be adjusted by the user.

In the DSC Tuner software, this minimum damping value is referred to as the Default Rate. The standard DSC Default Rate for 997.2 is 5% in Normal mode, and 20% in Sport mode. As driving load increases, the damping command percentage will increase up to a maximum value of 100%.

DSC can be considered a "equalizer" for the suspension hardware across the entire 997 model lineup since DSC commands the dampers in an active manner using nearly the full range of the dampers, whereas the stock controller uses a narrow range to make each model more distinct.”

While I cannot find the exact quote, my recollection is that the DSC box processes the sensor input data much faster than the OEM PASM box- and also utilizes all four channels of the existing PASM architecture, of which the OEM does not. Ergo, the OEM controller works F/R and side-to-side rather than individual inputs to each of four wheels to manage lean, dive, squat and (perhaps most significantly in my experience) uneven road surfaces that upset the chassis vertically, especially mid corner.

My PASM equipped stock GTS behaves dramatically better in linked off camber downhill tight esses with the DSC box. Night and day superior to the OEM box. Toss in (pun intended) some bumps, washboarded asphalt or heaves mid-corner and the DSC just shines.

Active (vice static) suspension better manages weight transfers and road irregularities. The software improvement/refinement evolution of the 997 through 992 chassis has addressed it via PASM, Dynamic Engine Mounts and PDCC.

It appears Porsche PASM programming, at least in the 997 series, failed to capitalize/optimize the hardware capability. That is a rare shortcoming from their chassis engineers.

The TPC box, at $1200, is both a marvel and a bargain.

 

Wait a minute.... something is wrong with that PASM description. It denotes acceleration sensors.... then why on .1 cars do you need to add the sensor with DSC. DSC denotes it does not exist on .1 cars.

https://www.dscsport.com/product/accelerometer/

Further, vertical control (ride height sensors) wasn't implemented until what, the 991? It reads like a description of Porsche's most modern system and not on our cars. I am confused...

I understand that the tech doc for the 2005 denotes all that stuff.... but my car sure didn't behave like it. BTW, I send Tom at DSC an email asking to weigh in here... I hope he responds.

Peace
Bruce in Philly (now Atlanta)

 

Pretty sure the 997.1 (unless it's a Turbo) only had two-axis accels so the DSC sensor adds the third axis. Later models have three-axis accels as standard IIRC.