BGB Motorsports

Does anyone else here think that the PSM is less intrusive on the race track than in years past and is actually a more user friendly PSM?

I can't remember the last time you could turn PSM off in a 997.2 and loop the car on the race track. In the rain I turned it back on at Barber. I just took the bone stock 991 C2S to Daytona and harassed GT3RS owners. 164mph in a stock street car with a passenger in the tri-oval is not too shabby! It was a bit too loose for civilian duty so when I had passengers, I had the PSM on. When I was alone, it was off but the car was much more "free" on entry.

Hudyman

PSM is definitely less intrusive than in years past, especially upon entry, power is suppressed on exit but it is not as perceivable. However, my lap times at NJMSP, Lightning are 1.5-2.0 seconds faster with PSM OFF.

Base 3.4 991 on street tires.

BGB Motorsports

Correct. Your car will be faster with PSM off, because you have eliminated the "yaw" control. With PSM on, if you over-drive the car down to the apex, the moment the steering angle sensor and lateral-g sensor determine a "yaw" event, they cut throttle and add brakes.

PSM - OFF - This allows you to remove the yaw control BUT you still have the wheelspin control at corner exit which is a form of traction control that will not hurt lap times as much as the fully functioning PSM and its being on.

Translation: I am not as quick to go deleting PSM on these new cars as we were with the older 987.2s and 997.2s. In fact, of the 3 track day customers that have asked to have their PSM disabled, we have suggested otherwise.

Cheers.

Hudyman

I have good helmet cam video from the track with PSM off that shows the PSM light flickering upon exit of the ski jump at NJMSP, Lightning. The car feels light, but stable in this section. I can't help think the 991 is deploying the ABD and throttle cut-off ever so slightly when that light is flickering. It is not perceivable to the driver but PSM is still on even when the button is "off", keeping my slip angle at a manageable rate. I would prefer a third setting where I could turn everything off ( for real). I understand that good Porsche mechanics can fully defeat the system and create a third setting with an added yaw control switch. Your client is correct in wanting that capability. If my 991 was a dedicated track car I would want the same.

The other major problem with not being able to defeat PSM completely is - using stock OEM brake pads is like throwing money in the fireplace. With PSM off I can barely get 2 days out of a set of OEM rear pads. Front pads are fine, but rear pads are toast after two days on track. The pads disintegrate into the rotor and cause a warped rotor feel upon heavy braking because their is so much material stuck in the rotor. The OEM pads are absolute garbage at high temperatures because the ABD is constantly engaging the rear pads when detecting the slightest slip. I wonder if a real LSD from Guard or OS Giken would solve some of this problem. The Porsche LSD doesn't do the trick... Would love a mechanics opinion here...

BGB Motorsports

I think you raced through my thread a bit too quickly. Remember, when you have "PSM - Off" you still have PSM in the form of wheel-spin control. So when you fly over the hump at NJMP and the car gets light, it loses contact patch and therefore slips the tire and that's what you see when you see the PSM light coming on and off. You are getting a physical indication that the rear calipers are grabbing tires at exit or in the situation of wheelspin. Anyone who says they don't see this light flickering is lying or not looking.

And in 99.9% of most situations, while the customer may almost always be right, if I have driven the car on the race track and it has come out from under me with 10 + years of professional racing experience, after having deleted the PSM entirely, in this case, I need to be the arrogant person and say that I am right and he is wrong.

It's all about setup and what is on the car. Our street 991 that is bone stock that has no aftermarket bars, no track alignment, just wheel spacers ...in its current state, with PSM off, is a handful. What kind of person would I be knowing this and sending a guy to Sebring in the wet with his PSM off before he has ever tracked the car? The guy was very green. He had never attended the DE and I did not think it prudent.

Your instincts are spot-on though with your solution to fix your disintegrating pads. What do you have? A 991 with a 7-speed manual? What you have in there is the equivalent of the LSD for PDK cars that are 987.2 or 997.2. So, while it is not an open diff, it is an LSD for all intents and purposes. But you are driving hard and really working the car and therefore the rear calipers are compensating for where the diff can't handle. I can't advertise that i can tell you that we can put your PSM on a 3-position switch.

Your gut reaction is 100% spot on. You need a mechanical solution. And while I may sound biased because we are the distributor for Guard Transmission for the limited slip differential that will work in all PDK 987.2s/997.2s/991s except those with PTV plus, if you are interested in a diff, I would love to try and sell you one.

Thanks.

John

Hudyman

Thanks John! Your decision making seems sound. I get where you are coming from, and as a DE instructor I appreciate getting into the passenger seat of a car with PSM on! For myself I simply wish I had a true defeat option so I could channel my old school driving techniques.

I have a local guy that can assist with Guard solution, he did good work for me with Guard on my Cayman S.

Thanks again for the great perspective!

BGB Motorsports

I appreciate the kind words. Speaking of DE and right side duty, we are working on a modern day version of the "Driver's Ed brake pedal" which will be something that guys like you can bolt to your existing Porsche Cayman or 911.

As for the LSD, have your shop call me. We are the sole distributor worldwide for this LSD. I can however sell it to your shop at a wholesale price if he's a Guard vendor, which it sounds like he is.

Thanks.

John

008

My 987S was certainly faster as you say with it off. I had a full defeat although I was never completely convinced it was 100%. 991S is coming soon so I'm glad to hear your thoughts on it. What are you guys running for wheels and tires? My understanding is there are no 18s that fit and no way to make an 18 fit. Obviously this is going to make tires very expensive as 19 R comps are limited. Also, any pics of this roll/harness bar that retains the rear seats?

BGB Motorsports

The "full defeat" is nearly 100% defeated HOWEVER when we tested all of this, we found instances of rear brake caliper line pressure coming on and off in 100psi bursts. The only way to truly remove it is to install the aftermarket ABS systems we have in the past and then re-link everything to the ECU via MOTEC.

Unfortunately, you don't have the option of running an 18 with the 991. One of the original roadblocks I encountered when trying to get the car classified for racing was the need for a 19" wheel and tire package; only 1 car in the entire Rolex series has been allowed to run a 19" wheel and tire. It also happens to be the same car that won the GT Championship 2 years in a row. Anywho...18s are very dangerous given the proximity of the inner bell to the lower knuckle of the new control arm design. You really really should run a 19" on there. Actually, I take that back. I tested the car on track and in wet conditions with a 19" wheel and tire package and it really changed the entire nature of the car. In my opinion, I know you don't want to hear this, but you should be putting 20s on the car and running what Porsche gives you. I know that I will probably be crucified for saying that but again, it was a wet day and I had the 20s off for new rubber and I had 19s on WITH SPACERS and the car was a handful on track in the wet.

I can have roll bar photos by Wednesday as we are still finishing up the 981 bar and not starting on the 991 bar til tomorrow. It will be raw steel but you will have an idea. I can certainly return and post photos.

On a final note, I think that those with the widebody 991 cars, C4S, Turbo, GT3, can run an 18" given how much more body there is in the form of quarter panel to hide tire and wheel. The narrower bodied cars like the C2S and C2 require a wheel offset and longer wheel stud that would take the face of the wheel out further than the body, requiring you to roll the quarter panels which, in my opinion is a NO NO on the new aluminum car. We have done a few 997.2 widebody conversions here where we have ordered the factory GTS, C4 widebody quarter panels and have installed them on narrow body C2s and C2Ss.

008

Terrible news! The only R comp selection that is worse and more expensive than 19s are 20s. I was hoping to at least be able to run Hoosiers on BBS or even take offs from a base.


Looking forward to the bar pics. Thanks for all the info.

BGB Motorsports

Hmm...let me go home and look at some tire math. If we can re-create a 19" wheel and tire with the same rollout, similar sidewall aspect ratio, etc, along with proper offsets we should be able to get you black to stock closely. An 18" is not an option.

008

I figured worse case scenario was I could use the base car's19s and get really close on tire size. I even ordered the roof rack so I could swap at the track with stocks if it rains, lose a tire etc.

j080808

I have the same problem with PSM on, per BGB that would make sense. I thought it was just me over braking since I am a newbie, but apparently its not? My dealer commented there was a lot of material on the rotors and that would coincide with my second track day where I was in the brakes much more aggressive.

paradocs98

Sorry to thread jack, but this statement has me concerned. It would seem logical that the best track setup would be the smallest diameter wheel that can clear the suspension and brakes--less unsprung weight, better and cheaper tire choices. John, what were the sizes of the 19" tires that you were running? Maintaining the stock overall wheel/tire diameter would require running something like 255/40-19 fronts and 295/35-19 rears. This obviously creates a taller sidewall, though--are these the sizes you were running? Do you think this setup creates more tire flex and sloppier cornering? Would it essentially be screwing up the chassis tuning that Porsche did, since they probably tuned the chassis for a 20" wheel setup with a particular sidewall height/flex? If so, would maintaining roughly the same sidewall profile as stock in the form of 255/35-19 fronts and 305/30-19 rears be a better match for the chassis dynamics? The downside with this setup would be that overall diameters are almost an inch less front and rear (although this would have the benefit of torque multiplication).

I'm about to pull the trigger on a 19" track and summer street setup, and I don't want to find out that I've made a mistake and defeated the chassis tuning that was done by the factory.

BGB Motorsports

Sorry for the delay. Yesterday was pretty hectic with us finishing up the 981 roll hoops and moving onto the 991.

I wanted to get back to you though because you want to order tires. No apologies for thread-jacking. I'm here only to help so, let's see if I can.

I failed to look at tire math last night but I would think that if you went to a 19" tire with the same rollout, just like you identified, you will be fine. As I think about it, the 19s I was on were fairly low profile. I don't think you can ruin the cars handling with more sidewall as much as you can hurt it without running enough. I think you are spot on as to why the car felt different. It drove like a car in the wet with too much sway bar. It felt too stiff because I had shot the relative spring rate of the tire through the moon by changing the profile. It needed more compliance in the wet, which is why we run soft springs and bars when it's wet.

I see so many people with 20" wheels and tires and a "ride" or "balance" that sucks because they don't keep the big sidewall. I don't think I would be concerned about adding sidewall as much as I would be concerned about not providing enough.

Make sense? And thanks for finally helping me understand why that went down like it did. Sometimes some mild discussion can shed light.

Cheers!