JCviggen

Manual GT3's are very fast on the straights generally, the lower losses and weight makes that once you're in 3rd/4th/5th you will pull a PDK car stock vs stock or modified. I went past a 992 RS like it was standing still on the long Kemmel straight when my engine and headers were still stock.

I have no doubt the setup is working well for you, but I would suspect that the intake is doing a lot of the lifting here rather than the headers. The stock GT3 ECU is limiting power and if you look to the excel screenshot I posted there was another car which got big gains from adding the intake on a base GT3 while his car was already on race headers and not putting in good times. The intake may be a way to brute force past some of the air flow targets of the stock ECU. With tuning I don't think the gains are necessarily worthwhile since the pressure drop across the stock throttle is not large. And there is always a pressure drop because without it the air wouldn't be moving, certainly not at the velocities you want.

On track it's also even harder than on the street for the stock ECU to keep running the optimal ignition strategies unless you have good fuel in the car - opening up the exhaust helps take some of the stress off.

It would be great if you had some GPS acceleration data to compare, but obviously I wouldn't expect anyone to go out of their way for that.

ParadiseGT3

Pretty remarkable gains with ecu tune. Have you ever translated that to lap time gains vs stock tune?

Lightweight wheels?

How much quicker did you find Cup 2 R vs CR-S?

Spa lap on previous page is a great example of how excellent the (full on) ESC + TC calibration is. I can basically never find any time with them disengaged, experimented ESC off again on the RS last weekend (with CR-S) in wet conditions, still no difference.

JCviggen

Yes, very significant gains unfortunately never did any back to back lap time testing as it's inconvenient. I don't get much time at the track generally, I fly in for a week, do a trackday and fly out again so I don't want to mess around too much with flashing maps in the pit lane and hoping I don't brick the ECU doing so.

Yes, Apex VS-5RS with the Nankangs and BBS RE-MTSP with the Michelins. However the tires themselves are a big weight difference and the farthest away from the center so I'd expect that to make a difference since the Nankangs are very heavy like 6lb per corner more than the 2R. However I can't really see a difference in acceleration between the two.

More than 2 seconds on a 2m30 lap. But that's not necessarily fair because the first flyer on the 2R is ridiculous. The second one it's already not quite as sticky, so the issue is learning quickly enough on the first lap to get the most out of it. VERY difficult unless you slap on a new set of them every week to get used to it. I buy like 2 sets a year. On my "record" lap (not yet on youtube) I definitely left a bit of time in the final braking zone as I erred on the side of caution and all the brake point references I used to have there have gone.

The Nankangs seem to have gotten better since I first used them, they're about halfway now I think and still fast and fun to drive on.

Could not agree more. On most tracks it really doesn't get in the way until you were already losing time. The one instance where you can go faster is if you have to jump a kerb, at Zolder the other day there was a chicane and you'd catch some air going over the second apex kerb and then the TC was cutting in and delaying power. I would've turned it off later but the rain came and stopped the fast lapping. At Spa there are some very quick corners where you always get a couple of snaps at some point during the day at 110-120 MPH and then it's nice that the ESC/TC is there just to give you confidence knowing that it's not going to develop into a massive sideways angle.

ParadiseGT3

Tire weight mention is interesting. I'm exploring a straight-line acceleration loss with CR-S vs SMR 2 / Cup 2 on the RS. It's showing consistently in lap data. 2nd through top of 4th gear acceleration runs, with the difference becoming more pronounced at the higher speeds, from shift point to the top of 4th gear.

The loss is many tenths per lap over a 2.2 mile lap -- maybe about 0.5 -- which is more than offset by braking and cornering advantages of the CR-S, but still a pretty significant straight-line deficit. You haven't seen similar comparing CR-S to Cup 2 R?

CR-S are 3-4 lbs. heavier per corner than SMR 2, and 4-5 lbs. heavier than Cup 2 R in RS sizes. Cup 2 R are tempting, but in my neighborhood "fast lap" season = traffic jams, so the limited use window of the Cup 2 R would be tough to exploit. Still will have to find a way to try them at some point... I'd like to see what equal or better braking & cornering grip and notably less weight would mean.

(Also pending a switch from Girodisc to PCCB, which I've never run. Cup 2 R & PCCB would be a 50-60 lb. advantage in unsprung, rotating weight as compared to CR-S & Girodisc.)

Look forward to your additional updates and findings.

JCviggen

Truth be told I haven't taken a fine comb to the GPS stuff, it's tricky anyway because the CR-S tends to do better out of slow corners than the Michelins. I've been looking at the delta in 2nd/rd gear where I expected most of the difference and didn't see any big difference but of course a few hundredths here and there add up over a lap. I can believe a few tenths lost over a long lap to the extra rotational mass. They're still probably my favorite tyre now for trackday-ing not record chasing.

I spent a LOT of money getting into a low numbers day at Spa. Usually you have to be really lucky to get a lap in. I got to do a max attack lap right after the out lap and the grip was insane. But if you have to abort and go again it will be down a couple of points right away.

ParadiseGT3

Yeah, not to spam your awesome thread with my own data, but this is what I'm seeing across dozens of acceleration traces CR-S vs SMR 2, various days, ambient conditions, etc. CR-S to SMR 2 being the only changed performance variable. Loss of straight-line performance is consistent. Would be interesting if you ever dig in and find the same.

As you suggest, CR-S (red trace) maintains a higher min speed through and is more convincingly out of the 2nd gear corner. But then the cross over occurs top of 2nd and grows into fourth approaching 120 mph. CR-S loss is about 0.14 on this straight. Along with being heavier, > CR-S rolling resistance could also be a factor. But yes, overall such a superior track focused tire. Acceleration data doesn't have me reconsidering SMR 2 or Cup 2, but combination of lesser weight & superior grip, will have to give the Cup 2 R a shot at some point.

JCviggen

I had a quick look at my data, accel looks not as affected as yours to be honest... both the pit straight and subsequent run down and back up the hill are hitting about the same speeds. Check out the attached .vbo (had to zip it because the other format was rejected)

The 32.6 lap is Nankang, 30.3 is Cup2R. Obviously I am braking later on the cups but the speed traces are pretty much symmetrical up to that point.

markiegt3

Look forward to the YouTube upload of the cup2r lap soon, JC

JCviggen

All right then. TBH I find it less fun to look at than the Nankang lap, and I'm annoyed by some time I left at the beginning and end, but the middle part of the lap was lovely. The deceleration at the end of Kemmel is just absurd really.

markiegt3

Great lap! Not seen faster a faster production gt3 lap on the internet yet, albeit I understand the circuit is faster now than last year

JCviggen

The unofficial record was a 991.2 GT3 RS MR doing 33.1 a few weeks ago. I'd have taken it by about a second but because of a partial repave it's closer to 3s now.

9914s

What timing device are you using? Nice lap BTW.

ParadiseGT3

Killer lap! Less drama than the CR-S lap for sure. Same sizes/specs between the CR-S and Cup 2 R? The R's held on pretty well for 2 consecutive laps.

Recognize your Kemmel brake point as just shy of where I hit them in a GT3 on iracing that's ridiculous.

Shout out to the finicky tpms system for not recalibrating in time and making you fly blind lol.

ParadiseGT3

Also just noticed K1 Cup 2 R, do you not have the Porsche N0 spec available over there? Both specs available here.

TDT

Only the front Cup 2 R N rated, might be available, since GT4 RS has them as an option and runs same size tyre as 991 GT3

Don’t believe there is N-rated Cup 2 R, available for the rear for 991 GT3.

Hence use of Ferrari rated.