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Join Date: Sep 2010
Location: Cucamonga CA
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987.2 Cayman PSM intrusion and rear brake overheat

I have a 2009 2.9L PDK car with 10 track days on it. Previously drove a BSX Boxster with 100 track days. Advanced driver/instructor, car is full weight with gt3 arms, springs, and alignment by 911Design race shop. Tires are NT-01 and brake pads are Raybestos ST-43 racing compound on stock rotors with Motul 600 fluid. As far as I know my car does not have LSD and does not have Sport Chrono. I experience periodic PSM intrusion and rear brake overheat/boiled fluid depending on the track configuration, smoothness of surface, and driving style.

Things that seem to aggravate the problem and boil the fluid:
-trail braking
-rough braking zones causing ABS activation
-squaring off a double apex corner
-using ALL of the gators which sometimes unsettle the car
-running tires that do not maintain factory diameter stagger

This car is now 7 years old and I find it strange that no one has found a definitive motorsport solution to unwanted PSM rear brake intervention resulting in overheat and boiled fluid on the track. Improving rear brake cooling is a good start but seems like a band-aid solution treating the symptom, not the problem. The problem is a whole bunch of unwanted PSM rear brake activity to smooth out your line at a time when the driver wishes to intentionally unsettle the car a bit during corner entry or exit. How can we roll back the PSM sensitivity so Fritz the Electronic Brake Wizard gets out of our business. On a racetrack brakes are slow and I want them only when I call for them with my right foot.

Others have disabled the yaw sensor which helps but adds a bunch of unwanted side effects including dash warnings, no oil level display, and affects ABS.

I really expected this 2009 2.9L PDK car to turn much faster laps than my old 1998 2.5L Boxster but so far this is not the case. It is much faster in a straight line, but the data shows it is much slower in the corners as Fritz the Electronic Brake Wiz intervenes and interferes with my judicious use of slip angle. Driving very tidy helps some but is still pretty slow compared to my lap history data on the same track with the Boxster. Fontana and Laguna Seca seem to be quicker with little rear brake intervention, but WSIR, Chuckwalla, and Streets are unbearable.

Does anyone have any new ideas to roll back PSM electronic brake intervention and get Fritz out of my business? Background electronic braking is damn slow, and boiled brake fluid is damn dangerous. Since PSM is software based I am thinking we probably need a software solution that offers variable PSM such as: Street (stock PSM), Sport (like sport chrono), and Race (zero PSM rear brake intervention without all the negative side effects of disabling the yaw sensor).

Fritz! I know what I am doing!
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2009 Cayman PDK
With a few tweaks
Old 02-22-2016, 11:33 AM
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gearhead
 
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We have found the addition of a proper LSD to have a significant effect. The logic behind why it works is that it reduces wheelspin and speed differential between the rear wheels and thus makes the PSM less intrusive.
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1974 914 Bumble Bee
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Old 02-23-2016, 07:33 AM
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That may be part of the solution Matt along with adding Sport Chrono to the car. I think a good LSD always makes the car more planted going in and coming out of corners by reducing inside wheel spin. I would also love to see a motorsport PSM software solution so the driver can dial-in how much rear brake PSM intervention they want.
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2009 Cayman PDK
With a few tweaks
Old 02-23-2016, 01:11 PM
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gearhead
 
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Everyone I know who races the car completely disables it. In the top classes they rip out and completely replace the ABS with a proper Motorsports unit. Hacking the oem software is too difficult.
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1974 911 Restorod
1986 911 Cream Puff
1974 914 Bumble Bee
2008 Cayman S Mule
Old 02-23-2016, 04:18 PM
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Yep, the desire to RIP IT OUT haunts me.

It's like "Lets make this really awesome handling car and then cut it's balls off when driven over 8/10ths in the corners." WTF
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2009 Cayman PDK
With a few tweaks

Last edited by Cajundaddy; 02-23-2016 at 04:42 PM..
Old 02-23-2016, 04:38 PM
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gearhead
 
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There's another group who feels that the PSM emasculates the driver and robs him of his racecraft. Different strokes for different folks.
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1974 911 Restorod
1986 911 Cream Puff
1974 914 Bumble Bee
2008 Cayman S Mule
Old 02-24-2016, 05:03 AM
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cay cay is offline
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Where you able to solve the problem?
Old 10-11-2017, 08:00 PM
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