Calling 997 autocrossers...
06-17-2011, 01:28 PM
#76
Rennlist Member
use of proper terminology is a key. 'bleeding air', 'stiffer suspension', it is pretty much meaningless.
you have a dynamic model - tires, lower control arms, camber, springs, shocks with classic 4 adjustments model (fast/slow compression/rebound), anti-sway bars - all suspension parts should be considered in a complex. words 'stiffer/softer' by befault apply to valving.
stock suspension is tuned for street driving conditions, with stock PS2 tires side walls stiffness. and speaking of AX in general - it is very close setup wise to regular street driving and benefits from softer suspension in general, much softer than real stiff track setups. as it was seen plenty of times - stock 997.2 SPASM is great, regular PASM is not bad too, in both you run AX with 'sport' off so shocks valving is set to softer setting. AX likes soft shocks. amount of sway and springs should be set to maintain proper contact patch on your tires while using particular camber.
anyway when you start rebuilding car for sports you change a lot of parameters. first you decide on what tires to run. street tires, DOT r-comps, hoosier R6/A6, hoosier R100/R80 or other racing slicks all require different setups. that is why there are stock classes where all driver compete on stock cars with predictable parameters, close to what factory wanted it to be. If one decides to rebuild and move into improved class - god speed, it is exciting and expensive experiment. from what i can see, it is not going to produce good results with stock street 997 car, you cannot make a cup car out of it no matter how much you spend. if one wants to AX competitively on 997/966 - it was told before - best current choice is 996 gt3 car, due to its stock paramters and current SCCA classification. if you want fastest porsche possible - get a 997 cup.
to speak of 'bleeding air' - decide first of what tires you speak here. Kumhos V710, Hoosier A6, Toyo R888, Toyo RA1, kumho V70A all demand different setups for best optimal control of tires slip angle and maximum traction is maintained a bit differently. Stock street tires are fine with any pressure.
From my experience any DOT r-comps with tread are not really dependent of precise pressure control 3-4 PSI of fluctuation will not ruin your day so if you are at mid-30 psi with 2-4psi more on rears than on fronts - it`s all fine, just do not exceed 40psi. With A6 tires you need to be much more in control to keep them at max traction zone as A6 tire heats up very fast and gains a lot of pressure, that is why you see people filling them up with nitrogen, spraying them with water or putting thermo bags on them in cold to maintain remaining heat between runs. doing same to street PS2 tire would be complete silliness.
as of 'lag' - there is no lag problem in 997 NA cars. turbo cars have lag problem. there is non-linear throttle response in NA cars. most of ECU flashes eliminate that setting it to 100% response all the time. again, it mostly is a non-issue. much more important issue is a linearity of torque - when you go through a sweeper on throttle steering and keep adding up you need you power to be maintained or you will loose traction and slip out.
PSM role. PSM is created and intended not to let car to spin in a turn. that whole behavior completely changes when you start using your steering input for braking and rear wheels for steering. when you`ll get to this point you will see why PSM should be off as it starts engaging constantly as it is not how car was intended to be driven on a street. it is different from situation when PSM engages in its classic classic 'please save me' mode when incompetent driver smashes throttle down to the floor in the middle of the turn. it was stated correctly that first one should learn how to drive 911 car with PSM to learn smoothness and how to control this extra weight in rear without spinning out in the turn. when it is learned and you know how to drive 8/10 without causing PSM to interfere you turn it off and learn how to drive 10/10 and 11/10 - exceeding front traction and maintaining 10/10 in rear.
you have a dynamic model - tires, lower control arms, camber, springs, shocks with classic 4 adjustments model (fast/slow compression/rebound), anti-sway bars - all suspension parts should be considered in a complex. words 'stiffer/softer' by befault apply to valving.
stock suspension is tuned for street driving conditions, with stock PS2 tires side walls stiffness. and speaking of AX in general - it is very close setup wise to regular street driving and benefits from softer suspension in general, much softer than real stiff track setups. as it was seen plenty of times - stock 997.2 SPASM is great, regular PASM is not bad too, in both you run AX with 'sport' off so shocks valving is set to softer setting. AX likes soft shocks. amount of sway and springs should be set to maintain proper contact patch on your tires while using particular camber.
anyway when you start rebuilding car for sports you change a lot of parameters. first you decide on what tires to run. street tires, DOT r-comps, hoosier R6/A6, hoosier R100/R80 or other racing slicks all require different setups. that is why there are stock classes where all driver compete on stock cars with predictable parameters, close to what factory wanted it to be. If one decides to rebuild and move into improved class - god speed, it is exciting and expensive experiment. from what i can see, it is not going to produce good results with stock street 997 car, you cannot make a cup car out of it no matter how much you spend. if one wants to AX competitively on 997/966 - it was told before - best current choice is 996 gt3 car, due to its stock paramters and current SCCA classification. if you want fastest porsche possible - get a 997 cup.
to speak of 'bleeding air' - decide first of what tires you speak here. Kumhos V710, Hoosier A6, Toyo R888, Toyo RA1, kumho V70A all demand different setups for best optimal control of tires slip angle and maximum traction is maintained a bit differently. Stock street tires are fine with any pressure.
From my experience any DOT r-comps with tread are not really dependent of precise pressure control 3-4 PSI of fluctuation will not ruin your day so if you are at mid-30 psi with 2-4psi more on rears than on fronts - it`s all fine, just do not exceed 40psi. With A6 tires you need to be much more in control to keep them at max traction zone as A6 tire heats up very fast and gains a lot of pressure, that is why you see people filling them up with nitrogen, spraying them with water or putting thermo bags on them in cold to maintain remaining heat between runs. doing same to street PS2 tire would be complete silliness.
as of 'lag' - there is no lag problem in 997 NA cars. turbo cars have lag problem. there is non-linear throttle response in NA cars. most of ECU flashes eliminate that setting it to 100% response all the time. again, it mostly is a non-issue. much more important issue is a linearity of torque - when you go through a sweeper on throttle steering and keep adding up you need you power to be maintained or you will loose traction and slip out.
PSM role. PSM is created and intended not to let car to spin in a turn. that whole behavior completely changes when you start using your steering input for braking and rear wheels for steering. when you`ll get to this point you will see why PSM should be off as it starts engaging constantly as it is not how car was intended to be driven on a street. it is different from situation when PSM engages in its classic classic 'please save me' mode when incompetent driver smashes throttle down to the floor in the middle of the turn. it was stated correctly that first one should learn how to drive 911 car with PSM to learn smoothness and how to control this extra weight in rear without spinning out in the turn. when it is learned and you know how to drive 8/10 without causing PSM to interfere you turn it off and learn how to drive 10/10 and 11/10 - exceeding front traction and maintaining 10/10 in rear.
06-17-2011, 02:46 PM
#77
Race Director
PSM role. PSM is created and intended not to let car to spin in a turn. that whole behavior completely changes when you start using your steering input for braking and rear wheels for steering. when you`ll get to this point you will see why PSM should be off as it starts engaging constantly as it is not how car was intended to be driven on a street. it is different from situation when PSM engages in its classic classic 'please save me' mode when incompetent driver smashes throttle down to the floor in the middle of the turn. it was stated correctly that first one should learn how to drive 911 car with PSM to learn smoothness and how to control this extra weight in rear without spinning out in the turn. when it is learned and you know how to drive 8/10 without causing PSM to interfere you turn it off and learn how to drive 10/10 and 11/10 - exceeding front traction and maintaining 10/10 in rear.
06-17-2011, 03:18 PM
#78
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An observation is that autocross driving is different than track driving, and some people seem to be assuming they're the same. They're similar but not equal.
I agree with most of what utkinpol just said for autocross. One slight disagreement is on whether the stock suspension is stiff enough, though perhaps 997.2 SPASM is. I do agree that the spring rates hard-core track drivers use are almost always way too much for autocross. Second niggle is that I personally like to have more fine control of the tire pressures, both in terms of lowering them to get better grip (using rollover, pyrometer, and feel) as well as changing the front/rear bias to get adjustments to handling that I can't get other ways (given non-adjustable shocks and stuck with alignment settings for the day). However if you haven't done more than ~ 20 autocross events, then I think utkinpol is right on: get tire pressures in the ballpark and drive the car. You'll go faster if you do that than fiddling with tire pressures.
I agree with most of what utkinpol just said for autocross. One slight disagreement is on whether the stock suspension is stiff enough, though perhaps 997.2 SPASM is. I do agree that the spring rates hard-core track drivers use are almost always way too much for autocross. Second niggle is that I personally like to have more fine control of the tire pressures, both in terms of lowering them to get better grip (using rollover, pyrometer, and feel) as well as changing the front/rear bias to get adjustments to handling that I can't get other ways (given non-adjustable shocks and stuck with alignment settings for the day). However if you haven't done more than ~ 20 autocross events, then I think utkinpol is right on: get tire pressures in the ballpark and drive the car. You'll go faster if you do that than fiddling with tire pressures.
06-18-2011, 12:40 AM
#79
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[...] it's also important to recognize that there are different iterations of PSM. With PDK and sport plus mode engaged, for example, the intervention threshhold for PSM is very high. In no way is it "engaging constantly" and it rarely interferes with your ability to place the car where you want it [...]
In a dot two, you don't feel it engage and you don't feel it disengage. You have to notice the light to be sure anything is going on. Unless of course you're intentionally using the PSM to go faster. Then you'll notice it does.
Gary
Last edited by simsgw; 06-18-2011 at 04:28 AM. Reason: Removed 'rockon' because it drove me nuts when I read the page.
06-18-2011, 12:45 AM
#80
Race Director
I won't know without borrowing a car to test, but I'm beginning to suspect some major changes between PSM in a dot one and our dot two, Mike. As you know, I experimented with intentionally waking up PSM during a DE day. What you say is certainly true, but I'd go further. If you're already a smooth driver, you never will feel PSM actions. You can see the effect of PSM, but you can't feel it doing anything. Certainly, it does not engage and disengage in a fashion you can detect.
In a dot two, you don't feel it engage and you don't feel it disengage. You have to notice the light to be sure anything is going on. Unless of course you're intentionally using the PSM to go faster. Then you'll notice it does.
Gary
In a dot two, you don't feel it engage and you don't feel it disengage. You have to notice the light to be sure anything is going on. Unless of course you're intentionally using the PSM to go faster. Then you'll notice it does.
Gary
