Yomi

Edit: Answering some of these questions after some AXs:
- tire pressures for stock MPSC2: 32F / 35R work well for me. I've run 30/33, 31/34 as well and they all are fine.
- I'm very happy with front middle (stock setting), rear hard (inner holes) for AX. I have not run other settings for comparison.
- No alignment data, but most comments involve people wanting as much camber as they can get, to the limit of the rules, and would still prefer more. My pyrometer says the stock alignment isn't horrible.
- in dry, all buttons on -- exhaust, sport, PASM, ESC and TSC off. It's possible to drive like a hooligan with the back end way out during tight sweepers, but doesn't feel like it wants to swap ends. Easy to give it some extra gas to help tighten up in a turn. No wet data, but unless there is standing water I'd run the same.
- Based on our events with 3 GT4 drivers, and results people are posting from other areas, it seems very competitive at regional events, even in completely stock form including the stock street tires.


I just got a GT4 and will be racing it in our PCA Showroom Stock class. Basically everything must be an orderable configuration other than tires (which must be the exact OEM size and 140+ tread wear), and you have to run with everything that came with it (e.g. spare, jack, etc.). So no fun modifications, but on the other hand, no temptation to go down the race-car path and no futzing with race tires before and after events.

Looking for advice on autocrossing setup (what little is allowed) for first time. I'll update after some events with what I find works for me. This is PCA which is mildly competitive, not hard-core SCCA.

At the first event I suspect most of this is rather moot, as I'll be working on understanding the car. It's been over a year since my last autocross so I'm sure I'll be very rusty. But it wouldn't hurt to hear some thoughts. My #1 thing would be seat time, preferably in a 50-run test and tune, but that isn't in the cards.

(1) tire pressures. These are the stock Michelin Pilot Sport Cup 2 tires (when the RE-71R's come out in OEM sizes later this year I'll consider them). I'll use the insertion pyrometer to get a better feeling for this, but for now, thoughts on hot pressures? I was going to ask about TPMS vs. gauge but it seems that's been answered: TPMS is not a good source of accurate current measurements. I'll stick to my trusty old 4" Intercomp.

(2) swaybars. Currently the shipped middle setting for front and rear. I'm getting the dealer to put the front one on soft, as quite a few people comment about understeer, while to my knowledge nobody is complaining of oversteer. For tight autocross stuff it would seem like more front grip would be useful. OTOH big front swaybars have advantages and maybe camber + tire pressures + driving can alleviate slow corner understeer enough to make the middle setting better...

(3) alignment. I haven't touched or measured this, so it is whatever came from the factory/dealer. If I can get enough heat in the tires, the pyrometer should give answers about camber. My Subaru needed truly ridiculous amounts of front camber (and still ate the front shoulders like crazy) and rear toe out that made alignment techs very uncomfortable. The 996 C4s seemed much more tame, with no obnoxious front tire wear even with camber at the max-stock equal-both-sides camber amount of 1.x degrees. I'm hoping the GT4 will be similar.

(4) Turn on sports suspension? It'd seem like a good idea unless the track is extremely bumpy. Looks like most people recommend using it on the older Caymans.

(5) I assume no harm with the Sport and exhaust settings. Rev matching on up/down shift may or may not be helpful for me (not like I'm ever going to be in 3rd), and the exhaust setting might make some corner workers smile.

(6) ESC off and ESC+TC off. I imagine I'll experiment with those, and eventually run with everything off. But curious to hear what people think of these. I rarely had the PSM on the C4S engage so it didn't matter a huge amount, but people with older Boxsters used to tell me that it was awful for AX on their cars. I can also find people that say they were constantly interrupted by PSM on their 2005+ Caymans so who knows. Could be driving style plus PSM generation plus tires.

Anything else?

edfishjr

What jumps out at me is the fear that you may think that autocross info relates to multilap racing. I don't think they do, much. My thoughts, in general:

Multilap: tire pressures start very low due to huge gains as the tires heat. Dry Nitrogen helps.The final operating pressure/temp has to be the goal and this takes track testing to figure out. Autocross experience is almost useless.
Autocross: figure out what starting pressure works best and keep bleeding between runs, generally. Pyrometers are useless. Tires never get to Multilap temps. Never need track pressures to support high speeds, but may use high pressures for other reasons. Must keep street tire core temps low or you will drive better but get slower each run and not know why as the surface overheats due to lots of sliding necessary to be fast.

Stiffness/balance tuning: experimentation at autocross can give some sort of track baseline, but expect big changes for the track. Generally faster speeds induce oversteer. If you attain a very responsive car at autocross it could easily be quite dangerous at 120. Tone it down toward more stability, slower response for the track. If the track setup feels a little dead at autocross it's maybe ok and will still be a handful at the track.

You have great alignment adjustability and you will need to learn how to use it to be fast anywhere, I expect. Minimum get some toe plates and carry a jack to all autocrosses, experiment and you will become the GT4 expert!

I know nothing about the nannies.

Good luck!

Yomi

Thanks Ed. This was all for autocross, since this is in the autocross forum. Track setup would be completely different (ad not something I'm at all concerned with at the moment). It seems the answer is "find out for yourself."

Mussl Kar

Run with nannies on for a few runs and then with them off. This will help you learn the cars limits. Not sure when I am doing my first autox but I do have full hard in the rear, mid in front. For sure I will be throwing it about. Will I spin? Good possibility.

jpgunn

Yomi,

Run rear bar full stiff and the front in the middle. Max the front camber as delivered from factory by sliding the upper strut perches all the way in. You should pick up about 1/4 degree or more per side and toe will be just slightly out. Mark before you move, and it is easy to set it back to stock between events.

Tires -- run between 33psi and 35psi hot. I start around 29F/30 rear, but have to bleed a little. Depends on the lapping setup of your events. 35PSI hot seems to be a good target.

Nannies -- No need for them. Turn on Sport and Exhaust, turn off all the nannies.

If you want to go crazy, lower the car 3 or 4 turns of the spring perches on each corner, put some 8mm LCA spacers in the front to get -2.7 with slight toe out, and max the rear camber to get around -1.9 with 3mm toe in per side. You are still Stock legal in this config, and the car works well.

Beyond that, I think spring changes are needed to make a big difference.

Yomi

Thanks for feedback. Nothing beats seat time, and I'll get most of this narrowed down after a few events, but I'm always trying to get more data.

I will probably do nannies on the first couple runs (looks like they got 7 runs at the last event), then turn them off. Barring lakes of standing water (it's happened) best to have them off in the long run.

I see both of you recommend mid/hard for the bar configuration. Given that in theory these are easy to adjust, I can start there.

Sounds like tire pressures are pretty normal (not 20 something or 40 something). I found a few other sites that recommend the 33-36 range so that's good to know people are agreeing on general pressures. Of course there are a lot of variables in the car, driver, and conditions for how pressures change over time.

My front lip is scraping on my driveway already, plus just about every business entrance around here, so lowering doesn't seem like a good idea yet, but amazing that's available on a stock car. Good point on camber solutions.

Yomi

First event done, learned a few things, still lots more to do. I'm too choppy and driving too point-and-shoot and not enough momentum. OTOH, I think that's always true, it's just the degree that changes. Dry, overcast, about 55F.





2016-04-10 PCA autocross

Won the class, 3/85 raw time overall. Not bad for a stock car on street tires. The other stock GT4 was dual driven and was only 0.277 behind, and the second driver would have been under 0.5 behind if he'd had a clean fastest run. I brought my new GoPro but couldn't get it to connect to the phone when on grid, and after I took it out of the mount to poke it after 4th run it looked like it was dead. So no video.

I had the swaybar set on middle front and full stiff in rear. I didn't notice any understeer, and in turns the throttle was able to easily steer the back end, without any feeling of it ready to break loose entirely.

For tire pressure I settled on 32F, 35R. That felt decent and looked good with the traditional shoe polish. It could have gone down a little more I suspect. The insertion pyrometer seemed to indicate these were working (all but one tire had the middle temp between the inner and outer temps, and that one was just a little high). Temps overall were low (fronts 100-115, rear 94-105), no indication of extra camber needed, but I remain dubious given it wasn't able to build up enough heat. I'll get an alignment done one of these days and see how close to -2.5,-1.5 I can get.

I ran with TC/ESC on the first two runs. Turned them off for the rest. No real difference from my point of view. Sport/exhaust/pasm on for all runs.

5500

First event this weekend.

Still running stock alignment (~ -1.3 camber F&R), SC2s, front bar middle, rear bar full stiff. 70 second course in 60* temps. Found good grip at 30lb F/33lb R hot pressures, console all lit up. Still pushes when overdriven, hard to rotate, otherwise very easy car to drive, very forgiving and responds well to corrections.

Should have alignment dialed in for next event, will add a bit more rear pressure to loosen the rear up if alignment doesn't help.

Mussl Kar

Thanks for letting me take a run in the afternoon! Can't wait for Saturday. I don't think I will have time for an alignment before then though. I will be running 235/35 19 A7s in front and 295/30 19 R7s in the rear. I'm hoping the slightly stickier A7s in front will balance out the car. I would like A7s for the rear but Hoosier has nothing close th a 295, other than a 315 which I am guessing will rub.
For the readers viewing, I offered 5500 a run in Kermit with reasonably fresh Hohos and he turned it down.

Yomi

What car is this not true about, particularly going too fast into a slow corner?

I've found it very easy to rotate if there's some speed and the engine isn't lugging, with just a little right foot application. Perhaps we're thinking of different things.

thigos

Great info here! Couple questions,

1)I thought that anything aftermarket wasn't allowed in stock (SS). So shims/spacers are ok?

2)Can someone explain the moving the upper strut perches in? Is there a link or pictures that would help show how to do this?

3)Does adjusting the perches dial in camber? And then you simply rotate them back to stock for more streetable alignment?

Thanks,
Matt

Drew_K

Good question. Shims and rotating the upper perches are legal per the rule book sections below. I believe this wasn't always the case and that a protest was sustained against a GT3 for rotating the perches (i.e., the GT3 was DQ'd). Someone please chime in if I have this wrong or you if you can shed light.

As for rotating the perches, search the 997 GT3 forum because it's been discussed in there quite a bit. It's as simple as it sounds (remove nuts, rotate, reinstall). And yes, it gets you more camber. I run 3.5 front, 3.0 rear, which I couldn't get in the front without rotating and shims.

From 13.8 of the rule book:

"B. Both the front and rear suspension may be adjusted through their designed range of adjustment by use of factory adjustment arrangements or by taking advantage of inherent manufacturing tolerances. This encompasses both alignment and ride height parameters if such adjustments are provided by the standard components and specified by the factory as normal methods of adjustment.

E. If offered by the manufacturer for a particular model and year, the use of shims, special bolts, removal of material to enlarge mounting holes, and similar methods are allowed and the resulting alignment settings are permitted even if outside the normal specification or range of specifications recommended by the manufacturer."

thigos

Great info Drew. So does 13.8.E mean that you could use adjustable toe links ("special bolts") as well?

What is the most complete suspension setup you could do and still be legal in SS??

Thanks!
Matt

mopar bob

However, no suspension part may be modified for the purpose of adjustment unless such modification is specifically authorized by the factory shop manual.

kjchristopher

Is rotating the struts in the factory service manual as a method of adjusting the front end alignment?