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Running naked

10K views 30 replies 14 participants last post by  Walter 
#1 · (Edited)
I replaced my 987.1 Cayman with a 987.2 version this past year, and have been learning the new car this track season. Initially, I was vexed by the fact that I was about a second slower in the 987.2, despite its horsepower advantage. Also, I noticed that the brake pedal was going soft late in the day, a problem I had not had with the 987.1. And, during bleeding, the rear brakes had an unusual amount of air in the lines. This was all happening despite the fact that I was running the car with the PSM switched off. Some searching on this forum revealed that Porsche does not allow PSM to be completely disabled with the switch, and that totally disabling all nannies required unplugging the yaw sensor. So, prior to my last outing last Friday, I unplugged the sensor, held my breath, and headed out on track. I was nervous because I didn't know what other effects might show up (for example, the cruise control stops working--not that I use that on track).

The car felt just fine without the nannies on, and I think it was quicker, though a GPS problem prevented me from getting lap times. The ABS still worked fine, and the brakes did not go soft as they had before. And-- the car actually got a bit loose while coming out of the slowest hairpin on the track when I romped on the throttle, something I had not experienced before. This all leads me to conclude that, unbeknownst to me, the rear brakes were still intervening quite a bit even though I thought PSM was off.

Overall, it was a fine result. The only downside was the fact that the car has a hysterical electronic panic attack when the nannies are turned off--I get a bunch of dire messages at start up, like "PSM failure!" and "Driver assist failure!" in addition to the "Flat tyre!" message I already get since the inflation pressures of my track tires are outside the normal window. The flat tire message is especially annoying, because, even if you toggle through it, it reoccurs at random times during a run session--distracting and disconcerting when beginning to brake from top speed. The car ends up wth the entire dashboard lighting up, with bells and chimes signaling imminent doom. When the low fuel warning light came on, I almost missed it, since it was practically buried in the throngs of other warnings.

I'm hoping to find a way to reprogram the computer to get rid of all these extraneous warnings and error messages. If anyone knows of a way to do this, I'd appreciate it. I suspect most shops will be jittery about doing it, for liability reasons, but I'll happily sign a waiver acknowledging that I take full responsibility for making the car into a virtual deathtrap.

Terry
 
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#2 ·
Disabling the yaw sensor was one of the best upgrades I ever did, it stopped all the nervousness under hard cornering and best of all , all my brake problems disappeared.
I now have a switch on the ground wire to the yaw sensor so it can be on if I ever use the car on the road and always of when on track.
 
#5 ·
A middle-ground alternative to the yaw switch is to have someone with a PIWIS to program your Cayman to think it has carbon brakes. Doing so reduces the threshold for PSM to kick in when the PSM button is "off".
My recollection from other threads is that disabling the yaw sensor will affect other systems. May not be important at the track but you should be aware of them.
Bern
 
#7 ·
Completely agree with disabling the yaw sensor. Before my first track day with my 987.2S I wired a switch for the ground so I could try it both ways. At first I tried with just the PSM off and the traction control light was still flashing all the time (even with a LSD) and you could feel the car being held back and intervening. Once I turned it all off, the car behaved as it should with the ability to rotate the car and get on the power without interruption. The car is so easy to control with everything turned off that it is somewhat annoying that Porsche won't let you turn off everything without rigging the yaw sensor. I can not image tracking this car without disabling the yaw sensor now.
 
#8 ·
I definitely prefer the 987.1 brakes to the 987.2. To me the .1 brakes are very linear with better modulation and the .2 brakes almost feels like a pressure plate to me and just like my SIM.
 
#9 ·
Biggest benefit from turning the Yaw sensor off when on track, apart from the better handling / driver control is:

Much less rear brake pad wear, especially the inside pads.
Less chance of overheating the rear calipers
Less chance of overheating the ABS pump.

Best part of turning all the driver aids of is that it become so much more rewarding to drive the car on track, you know it's you driving skills that get the lap times, not gadgets ;-)
 
#18 ·
I asked about Sport Chrono, because I do have it on my 2010 Boxster S and my experience regarding PSM is significantly different than yours. Sport Chrono opens the PSM engagement window such that it ceases getting in the way, and the other wizardry packaged with PSM, like dynamic brake bias adjustment, becomes a HUGE asset on the track, enabling much more aggressive corner entries, and faster lap times. It's a completely different car on the track in Sport+ vs normal.

I'm no national champion, but I am a 5-time state autocross champion and locally highly competitive in time trials and can attest that my 987.2S is fastest with SC in Sport+ and PSM left on. I think it may be a bit dangerous to be encouraging people to pull yaw sensors when what you really need is a SC retrofit (about $1k through a dealer, cheaper through an indie.)
 
#20 ·
I hope my thread was not interpreted as encouraging everyone to pull their yaw sensors. I'm just relaying what happened when I did mine. For sure, people should not perform this modification unless they have the experience and ability to control the car, and are willing to take the risk of a bad result. I did my first 15 years of track driving in a 944 that had no driver aids beyond ABS, so I felt confident enough to give it a try on the Cayman, but, even still, I took it easy until I was sure there would be no ugly surprises.

Please, everyone--be careful out there.

Terry
 
#22 · (Edited)
I agree with that, nielsen. I drove every autocross my first year in this car with psm off for this very reason. I run with it on now, not because I need to, but because I found the performance aids packaged with psm (dynamic brake bias in particular) really do make it a faster car than with psm disabled. I don't have PASM, but pulling the yaw sensor disables that magic pasm as well and leaves it full stiff all-around.

I don't pull the yaw sensor, as for sport chrono cars, turning psm off via the button in sport+ mode really does push it WAY out of the way as it stays completely off under throttle and the "always on" envelope under braking is so wide as to be pretty unrestrictive. Honestly, even with psm on, it stays mostly out of the way in sport+. (Horribly intrusive in normal mode, though; I can see why it's do despised by those without sport chrono.)
 
#25 ·
I am interested as well, but I have a 987.1S with a Wavetrac LSD. I have found that I need just a little more yaw before the PSM kicks in. With the LSD, it seems that the PSM does not completely close down the motor for a second or so, it simple retards it as it comes back very quickly now. With the PSM off, I feel that the LSD at apex will oversteer slightly, enough though to cause me to back off. The opinion of the autocross guys are to turn it off and leave it off. As others noted here, you start to rely on it. I feel that if I had a SC option installed, I could use that and then turn off the PSM. Or maybe leave both on and get more yaw which is what I am after.
 
#26 ·
I usually leave on unless it invers during an autocross (delays gas response) then switch it off. I've found few autocrosses that require it off. Maybe 1-2 a year. Of course you can go without it all the time; it's just a totally different driving style with or without. Not necessarily better just different and harder on the car. After 30 years of doing this I've found PSM will help you more than hurt you 75-80% of the time.
 
#27 ·
Augie- I agree with you that PSM is effective and of benefit most of the time. However, I am looking to modify my OEM setup slightly to include a SC software package to allow more slip angle at full power. That's the key is to keep full power available, yet allowing the LSD to give more forward thrust without snap oversteer that can occur if the PSM is off. My oversteer is not a spin, just more slip angle than needed to get the best time. This is a timed event so each 1/10 of a second counts. So, going from 8 degrees slip angle of the OEM system currently to 11 degrees with SC might be the right way to go. I will call Scott at Softronics to see if he included the software mapping for the SC/PSM interface with my race package upgrade 6 months ago.
 
#28 ·
I quite enjoy driving the car in Sports +, with the slip angles and how the car rotates so differently. However, without the delayed in freight, adjustable front control arms, the car does exhibit a type of understeer/4wheel powerslides. so I have to back off ever so slight, to get both the rotation and keeping the car on the lines
 
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