Post of the month at a minimum. Thanks for sharing.

 

I'm getting pretty significant outer tire wear after just 4 DE days, more so front than rear. I'm taking the car to Eurosport in Chicago tomorrow and can hopefully get more camber before going to Autobahn in Joliet on Monday. Am curious to see what the stock alignment #s come out to be.

 

A tip of the hat. As I get to grips with my new 4S and get to know the car that shows something new every day, its heart warming to read through a thread where I understand nary a word.

 

Impressive car, great information, thanks.

Do you have any heat soak issues? I presume you are running straight H2O and maybe WW.

Best, Bret.

 

No water wetter and H2O as it is still running the factory coolant. The race cars run ONLY distilled water and water wetter. This car is stock. The new cars are really targeted towards holding that 200 degree water temp. I have not seen any heat soak issues but I have heard of some guys at altitude during the summer months running warm. This stock 3.8S 991 lacks a center radiator however and that would clean up a lot of the issues as even just the added water helps.

They are truly great cars that can handle a ton of abuse.

 

Thanks John.
How long are your track sessions, and ambient temp?

 

Specifically for the 991, we haven't run the car longer than 20 minutes. However, we have been endurance racing the DFI Caymans and 997s for as short as 40 minutes and as long as 2.5 hours. Ambient temps range from 70 to 95 and in the summer months, the heat soak and the power loss is an issue for even some race cars.

The new 991 has no power steering hydraulics so there's a lack of 225 degree power steering fluid throwing through your oil cooler (987.2 only / not 997.2) and the gearbox/trans/diff fluid is cooled from the factory with a heat exchanger like the 997.1 GT3 so that helps things further. HOWEVER, the car really is designed to live/run around 200 degrees and easily heats up to and over 205 just sitting.

I would think that a center 3rd radiator would cure most all problems and I would think that those that DE/track at tight courses with 95 degree ambient temps should expect to see 200/210 and even 220 on the water if you run for longer than 30 minutes AND stop in the pits for tire pressures. You guys really need to try and find a way to stop 1 lap early and cool things down to about 65% and drive around the track staying off the brakes and just cooling things down. At this point radiator fans are running, engine bay fans are running and things are just hot. If you have an aftermarket cone-filter intake that is not insulated/sealed, your car will begin to lose about 40-60 horsepower at the wheels and things just get worse and worse.

Heat is the enemy of all things racecar!

 

Added the centre radiator a couple of months ago and went back to Road Atlanta twice since then. Temperature perfectly stable around ~200F under all circumstances. Never really had a problem before with the 991, but would rather play it safe.

Engine is 100% under control, but I keep killing my brakes (HP2000 pads on 15" Brembo's). A fresh set of pads would not last more than 4 to 5 hours on the track. A first option is to try the RS29... and a second option is to take it a bit easier and not stay full throttle/full brakes during the entire sessions. I did some quick math based on board chrono readings and peaking at 130mph on the backstraight vs 155mph only costs less than a second in lap time but reduces the brakes thermal load by more than 30%.

 

You guys have to remember that PFC, Hawk, Brembo etc all feel really good and will suck your eyeballs out under braking BUT they generate too much heat because they are for race cars with real brake ducts. Like it or not, if you are DEing or even club racing I would be telling you to put RS29 Pagid on and be content with improved rotor life and lower temps.

Those big pads will burn your car down at 10/10ths. You begin to soak the caliper fluid and you need that for your clutch hydraulics, so it becomes a downward spiral.

Get the Pagids; I don't get good deals on them so I'm not telling you to buy them because I want to sell them.

Trust me!

 

Thank you John, great info.

Best, Bret.

 

I tried to use 19''245/35 295/30 Advan 08 on track, but compared to stock 20''Pirelli(305 rear tyre) car became so unstable, it sliding on every corner, why?

 

I don't have personal experience with this particular tire but typically these types of tires are very sensitive to tire pressures. What hot tire pressures did u run?

 

tried different when hot it was 2,5 -2,6 , another setting around 3.0

 

I would definitely try to go down to 32-34 hot range. It may not seem that far off from what you've tried, but can have big impact on tire performance. Also, when I say hot pressures, it's when u measure right after you finish your track session, which means you start around 25-26 cold.

 

Keep in mind that braking hard for shorter amount of time is likely to generate less heat vs braking longer with less brake pressure.