semicycler

The shocks are filled with hydraulic fluid. There's a fixed flow path and an electronically controlled flow path inside each shock. The valve's position is proportional to the amount of current supplied to each shock in milliamps (mA). This controls the amount of fluid flowing and indirectly the dampening force of the shock. A fully closed valve is stiffest with fluid moving through the fixed path only (right image). Valve fully open is softest with fluid moving through the center of the shock as well as the fixed paths (left image). And there are valve positions in between continuously adjustable from fully closed to fully open. Fail safe is fully closed (0mA) and fully stiff.

According to Tom, OEM and B16's are closed at 400mA and open at 1500mA. Going below 400mA doesn't close it anymore so the floor is set here. Going above 1500mA doesn't open it any more but does generate more heat on the valve, so the ceiling is set here. Normally these types of control systems are not quite linear, but to simplify things let's assume they are. So to get to 50% damping, the control signal is set to halfway between 400mA (fully stiff) and 1500mA (full soft) or 950mA. 75% stiff would be 25% of the way between the floor and ceiling at 675mA. 75% soft would be 1225mA.

The shock calibration tables map control currents in mA's to percent stiffness. This is probably the only table you would adjust. You can narrow the range for a stiffer initial ride (1200mA to 400mA), soften the lower end of the range for street cruising but leave the higher ranges in place (flat 1500mA from 0% to 30% then scale down to 400mA as usual), or anything else you can dream up. I've softened up normal mode a bit for the wife but have found going too soft leads to a bouncy ride (underdamped). Most of the time I leave it in sport mode unless the road surface is really poor.

The other tables are used with various sensors to figure out what percent of stiffness to apply to each corner (g-force sensor, brake pressure, speed, etc.). Then a lookup is done against the shock calibration table to figure out the amount of current in mA's to send to each shock. By default there are two or three shock tables setup in the DSC controller depending on your model and they work quite well as-is.

Now with this all said, I'd love to see a "stiffness vs. mA" graph as you suggest to see how linear this control system really is.

Larry Cable

nice writeup! thanks...

sl951

Thanks for the description.

I don't see how one can really 'tune' without knowing shock velocities.

It sounds like the newer '2013' OEM shocks can measure velocities, can you data log this?

semicycler

Mine's a 997.1 C2S with B16's so no shock velocities, more like open loop tuning. I have captured logs for brake pressure, g-force and speed on a short repeatable path near my home along with the control values being sent to the shocks as a result. Then some offline Excel spreadsheet work, tweaks to the shock calibrations or other tables, and repeat until I'm happy with the handling. The logged shock velocity columns were always zero. I'd expect they would have real values if the shocks supported it though.

In my case I was trying to soften up normal mode to be used when passengers were in the car. I've replaced a lot of the OEM rubber suspension bits for monoballs and the like so the ride can be too rough at times with the wife in the car. Going too soft across the calibration table caused the ride to be softer but bouncy. Too stiff and it slams into each bump in the road but damps out real fast. I settled close to the stock normal setup just slightly softer. Sport mode is unchanged for now until I have some time to tweak values at the track. But even with the stock setup the car just hugs the corners when carving the back roads. I'm real pleased with the results so far.

motopix

semicycler,

Can you post your mode 1 settings? I don't remember seeing them in this or the 997 DSC thread.

semicycler

Sure, I need to pull them off the box though the next time I have the car out from under its cover. I've got about a dozen different versions on my laptop and don't remember exactly which one is the latest.

steve porter

I fitted my DSC yesterday and I am really impressed with the way that the car now doesn`t pitch and dive into tight, hard corners. It feels a bit surreal at first, as hard cornering, with what feels like zero body roll is usually associated with a stiffer bumpier ride,not a smoother better controlled one. Well done Guys, a very worthwhile and highly recommended achievement

Hatzenbach

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steve porter

I have since done a few brisk runs in the car on familiar bumpy mountain roads with familiar bumpy mates, and the composure and therefore the ease of speed of the car is improved leaps and bounds. It not only felt faster to me,but it was noted by others that my car seemed much quicker and more stable, for the short time they were able to follow it.
Also on this particular route the car used to bottom out (brake ducts I think) at least 6 or 7 times, whereas with the DSC it only did it once, and even then it wasn`t as severe. I really couldn`t be happier with the result of fitting this,and would highly recommend doing so to anyone who hasn`t.

Jono809

I've been using mine for about a month in the car now and it's a definite improvement, even driving normally if feels like there's more rebound and the car has lost that "floaty" feeling it has when previously driven in PASM normal.

I wouldn't say, for me, that squat & dive has been eliminated, it's been significantly reduced as has body roll on the street at least.

I took the car to our fastest local track last weekend, Phillip Island, and was able to take 1.5 seconds off my previous best lap time there. I also changed from Cup 2 to Dunlop Sport Maxx Race tyres - which should have had some benefits. The weather was also good in the first session when I set my best time, couldn't manage to go any faster throughout the rest of the day but was consistently within 0.7 seconds of my best time the whole day. I've also only been to this track twice before - so there would be time in that as well.

The car definitely felt better than it had done the previous time there in December. I probably had my tyre pressures too low as well, giving the car a softer feel, anyway - there's a lot of variables so read into it what you will. As has been previously stated by the DSC guys, it's just one part of the handling setup, it's a definite improvement without any trade-offs for me. I should probably get a second set of wheels and better tyres to get more out of the car anyway.

My best lap for reference, the camera was a bit loose unfortunately, but you get the idea. Much improved stability at speed.

Jono809

Which bumpy roads are these? I almost gave up on this car on our back roads before DSC! It was just back breaking...

steve porter

Top of the Reefton Spur to Marysville, Car always bottomed out savagely a few times on that road and only did once with the DSC fitted,and it was pretty mild, and the Meyers creek rd, Chum Creek road Loop.The car was sensational through there, with no bottoming out at all.

Jono809

Ah yeah, I know exactly what you mean, I used to bottom out around there a lot but haven't been back since I put the DSC in. Have they finished resurfacing Reefton yet? Last time I went there were tiny pebbles everywhere just hitting underneath the car

steve porter

still a bit of loose stuff, but pretty smooth with plenty of grip.

gasongasoff

Where can I download the tuning software?

It's a little too stiff on mode 3 when used with B16 coilovers on the street. Are there any changes to make right away to optimize the DSC for use with B16's on a 997.2S? Thanks!