GT3 Cup (997 Type) Tune needed

[Matio612]

Hi all,

this forum got my attention by numerous posts on FM.net where this board's members posted some great info on tuning. I'm still new to this art and hence would like to ask for your expert assistance.

I've been doing some race replica designs based on the 996 GT3, 997 GT3 and 997 GT3 RS. However, as I lack any tuning skills (which is something I'd like to chance) these cars come with the default Forza tunes. So, I was wondering if anybody could give me a helping hand and provide me with some easy-to-drive tunes for the cars mentioned.

Too make things a little harder (and more intersting) I would require the tunes wo work without the Forza Body kits (= standard aero).

The original idea was to come as close as possible to the real specification of the Cup cars.



Here's the info I collected from this page.


Background:

The new Porsche 911 GT3 Cup is entering the 2008 motorsport season with engine output increased to 420 hp.  The 911 GT3 Cup (997) was developed based on the current 911 generation, which has been gradually and successfully established in the market since the end of 2004.

The most significant modification compared with last year’s model is the new rear end following the design of the production model. Air venting slits ensure better dissipation of heat at the rear. The 3.6-litre six-cylinder boxer engine developed in Weissach is also based on the street-legal GT3 and develops maximum output of 420 hp, 20 horsepower more than on the previous model. The sequential six-speed transmission with interruption of engine power enables the driver to shift up under full throttle without disengaging the clutch. The transmission itself has been optimised and the gear ratios adjusted to the characteristics of the engine. Weighing 1,150 kg in race trim, the new 911 GT3 Cup has a power-to-weight ratio of 2.7 kg per horsepower.

26 units of the 911 GT3 Cup built for the Porsche Mobil 1 Supercup feature a special exhaust system with an even more striking sound pattern reminiscent of the Formula 1 racing scene as well as PCCB Porsche Ceramic Composite Brakes as exclusive highlights. Compared with conventional brake discs, PCCB reduces unsprung masses by 20 kg and sets new standards in terms of responsiveness, resistance to fading, and a long service life. The racing cars entered worldwide in the Carrera Cup feature a modified exhaust system and steel brake discs.

Power train:

    * six-speed sequential dog-type gearbox
    * gear ratios: ring & pinion gear 8/32 i = 4.0

    * 1st gear 12/38 i = 3.16
    * 2nd gear 15/32 i = 2.13
    * 3rd gear 18/31 i = 1.72
    * 4th gear 20/28 i = 1.40
    * 5th gear 26/30 i = 1.15
    * 6th gear 28/27 i = 0.96

    * pressure-oil lubrication
    * oil-water heat exchanger
    * single-mass flywheel
    * hydraulic clutch center-release mechanism
    * 5.5“ triple-disc sintered-metal clutch
    * limited slip differential 40/60 per cent
    * rear-wheel drive

Engine:

    * flat six-cylinder boxer engine
    * 3,598 cc, stroke 76.4 mm (3.01"), bore 99.98 mm (3.94")
    * max. output: 309 kW (420 hp)
    * max. torque: 420 Nm (310 lb-ft)
    * max. rpm: 8,400 rpm
    * four-valve technology
    * water-cooled
    * dry-sump lubrication
    * two-stage resonance intake distributor, central air intake
    * electronic engine management system MS 3.1
    * sequential multi-point fuel injection
    * required fuel quality: 98 octane ROZ, unleaded
    * racing exhaust with fully controlled catalytic converter (400 cells)
    * rear silencer with centrally mounted double tailpipe; special exhaust tailpipes for the Porsche Mobil 1 Supercup

Suspension:

Front

    *  McPherson spring strut axle
    * Sachs gas pressure dampers
    * double coil springs (main and ancillary spring)
    * adjustable sword-type anti-roll bar
    * front axle arms adjustable for camber
    * reinforced front axle crossbar with six-point fastening and double clamping
    * power steering with electrohydraulic pressure supply
    * three-piece BBS light-alloy wheels (9J x 18); ET 30 with central locking
    * Michelin rain tires (24/64-18)

Rear

    * multi-arm axle with rigidly mounted axle subframe
    * Sachs gas pressure dampers
    * double coil springs (main and ancillary spring)
    * rear axle track arm adjustable for camber
    * rear axle tiebar reinforced and infinitely adjustable
    * adjustable sword-type anti-roll bar
    * complete suspension infinitely adjustable (height, camber, track)
    * three-piece BBS light-alloy wheels (11J x 18); ET 43 with central locking
    * Michelin rain tires (27/68-18)



Here's the build info of my 997 GT3 RS.

PI: S950

Speed: 6.8
Accl.: 6.3
Brakes: 6.0
Handling 9.5

Power: 309 kW (415 PS)
Torque: 407 Nm (300 lb-ft)
Weight: 1,044 kg (2,301 lbs)

Engine and Power

Std.

Platform  and Handling

AP Racing Race Brakes
Hamann Race Springs and Dampers
Eibach Race Antiroll Bars
Porsche Race Transmission
Sachs Race Clutch
Euro Sport Race Flywheel
Porsche Race Driveline
Quaife Race Differential
Recaro Race Weight Reduction

Body and Aero

Std.

Tires and Rims

Michelin Race Tire Compound
Front: 245/35R19
Back: 315/30R19
BBS RE Rims

If anybody could provide me with a great tune (the gear info is alreay provided) it would be highly appreciated!
I'd happily pay 250,000 CR or gift a car for an easy-to-drive tune!

If you need more info please contact me... and in case of questions concerning which track to tune for... Laguna Seca would be #1.

Cheers

Matio

[Ske]

I'm also using Seca as a test track, so I guess I could take the car for a spin and see what I come up with. Could you add me and send me a car to work with?

[Matio612]

Oops.. just send you a Friend's request to gift you the car, but FM2 complains that it is a rare car (DLC) and as such cannot be gifted. I wrote down the entire spec. of the car I have in mind. standard engine and aero, platform parts are all rac parts and tires and michelin race tires, max width with BBS rims on. Should take about 2 minutes to setup...

As I cannot git it... you gotta buy it yourself. If you need the money, simply auction a mini for 220,000 CR and I'll buy it, ok ?!?

[feuerdog]

I'll post up some V5 suspension calcs for you.
 
I assume the stock front weight distribution is 38%?
Aero downforce is assumed to be 0/0.

Untested V5 settings:

springs 364/480
arbs 13.0/17.2
rebound 8.1/9.8
bump 5.0/6.1
caster 5.6
camber -.9/-.9
toe 0/-.2
tires 29/28
diff. 60/40
brakes 47/100

[bimmerlovere39]

Guys, remember - the GT3 RS comes stock with adjustable rear aero.  That can play a major role.

I'll look into making a standard 997 GT3 tune... no promises, though.

[bimmerlovere39]

This is where the way Forza does modifications becomes frustrating... we should have dry sump lubrication, a racing fuel cell (I'm guessing there, but I see no reason they wouldn't have one) and a racing muffler system, but that puts us ~996, including the Volk SE37Ks that, imho, look more like the BBS wheels on the picture car.

Shame we don't get any of the really nice BBS wheels...

PS: It says on the website that the diff is a 40/60 unit.


Edit: You say "easy to drive tunes" - you do realize we're talking Porsche, here, right?  No amount of tuning is going to make these things handle like a Civic - they are Porsches, and you have to drive them as such.  They are unique cars requiring unique driving.  That said, they can be tamed - to a degree.

Secondly, not to nag, but the point of this forum isn't for people to say "Give me a tune" and recieve it.  I (and I'd say many others) would be happy to help you tune it, but I'm not all excited about giving you a tune, especially when, from the way I read your post, it sounds like you are going to be slapping the tunes a multiple cars and selling them off on the auction house.

I for one am not interested in being paid credits for a tune - I'd rather help somebody else learn to tune.

[feuerdog]

With aero downforce at 0/100

Untested V5 settings:

springs 364/498
arbs 12.8/17.5
rebound 8.0/9.9
bump 5.0/6.2
caster 5.6
camber -.9/-.9
toe 0/-.2
tires 29/28
diff. 60/40
brakes 47/100

[Ske]

Do you have a target time or improvement in seconds over default? Also, can I change the FD ratio?

[Matio612]

hi ske, bimmerlover and feuerdog,

first off, thanks for your help. It is really appreciated!

@Bimmerlover: I see your concerns and I've started to read some of the basic documents (Shiny's side up! newbie tuning guide) as well as the weight bias tuning tutorial by Fit4AKing. However, as a non-native English speaker is's not that easy to understand... especially as all my menus are in German and the units are metric. All the documents are English and have English measurement units...

So, I'm in a middle of a learning process. And certainly I would compare the standard tune with the info I get from here.

I'm not 100% sure what you mean when you say that Porsche's are hard to drive? I mean it's a race car and as such needs to be handled with care, right? When I say easy-to-drive I mean that one does not need to feather the gas out of turns (e.g. as in these overtuned muscle cars) and that the car is hard to spin-out... that an average driver can post descent lap times after a few laps of getting familair with the car. 

@Ske: A descent lap time for an S-class car on Laguna Seca would be a 1:22 +/- one second IMHO....

Oh, and it's not my intention to rip people off by selling them tunes I got for free. No, it's just that I've started to replicate some 997 GT3s and would like to sell them with a descent tune. So that people get a nice experience... I guess the cars would sell equally well w/o the tune...

The car is targeted for a Pi of S950 without Forza Kit... so everybody that want's to push it into the LB (where there's no 997 to be seen at all) it would certainly require Forza kits, more power and lots of tuning adjustment. Still, there may be people out there who would love to setup a GT3 Cup Series by themselves with the cars as they are... here a good and (close to real world) settings would be great!

Well, here's a WIP picture of one of the cars:




@feuerdog:

• front weight distribution is 41%
• The limited slip differential in the real cars is set to 40/60 per cent

I'll test these settings ASAP, thanks for it.

[Matio612]

Do you have a target time or improvement in seconds over default? Also, can I change the FD ratio?

See, this is a very good example... for you terms like FD ration may be second nature, but I would have to guess... F? Differential ?!?
Please try to stay as close as possible to the posted values... if you defer please let me know for which reason so that I learn 

THANKS AGAIN!

[JG4tr]

FD would be short for Final Drive. The overall 'rear end' gear that is set in the transmission tuning section.

[Matio612]

FD would be short for Final Drive. The overall 'rear end' gear that is set in the transmission tuning section.

Which would be equal to what is stated as ring & pinion gear 8/32 i = 4.0 above right?

I'm no expert tuner, but I'd assume you would set the gearing settings on a per track basis, right? (As everything else as well I know...)

Not 100% sure how this is handled in the Porsche Super Cup: if these settings are fix and the same for each track or if the teams can twist that. So Ske, please change them as you see fit in order to get close to that Laguna Seca tim posted above. As the official settings are written down I could always apply them myself anytime again.

[JG4tr]

FD would be short for Final Drive. The overall 'rear end' gear that is set in the transmission tuning section.

Which would be equal to what is stated as ring & pinion gear 8/32 i = 4.0 above right?

Yes.

[Ske]

@Matio: I'm not a native English speaker either (from Norway), but I'm using imperial units in Forza just because they won't let us use HP with metric units... silly Americans I adopted pretty quickly though, and real world values don't translate that well into Forza anyway. And yes, most race cars have changeable Final Drives.

I ran only 3-4 laps at each stage in the tuning process to focus on ease of use... if I couldn't do a good time within 2-3 hotlaps, the tune is too unstable or hard to drive.

First run with a stock tune was a dissappointing 1:25.7 which is slower than my A class times. Car was mushy, unresponsive and understeery... And I had to shift gears all over the place.

Changed the Final Drive from 4.00 to 3.50 - 1:25.0, the shifting spots are just right now.

Checked alignment in telemetry, and adjusted camber to -0.8/-0.7 - 1:24.2, and much better to drive already.

Tires warmed evenly but reached 32 PSI before lap 2, so adjusted pressure to 28/28.
Still some understeer, so I did some trial and error with ARBs before settling on 12/20 - 1:23.7

It's balanced in corners now, but twitchy over crests and under braking. +100lb rear downforce gave me a 1:23.5 and a much more stable high speed ride.

Rear still locks up a bit when trail braking, adjust brake bias to 52% front. Same time, but it's now completely stable.

Need quicker and more stable turn-in, +0.1 front toe and changed dampers to 5.0/7.0; 2.5/3.5 - 1:23.3 and my best time.

Tried various spring rates and biases but found the default values close to optimal. I like round numbers, so 350/500 (lb/in) it is. Same times but feels a tiny bit more alive. Stiffer front than rear was not an option... wobbly at speed and hopelessly hard to turn in slow corners. 500/700 felt good, but quickly lost time if I hit a rumble strip wrongly. 280/400 seems to have potential for miracle laps, with a 1:23.6 first lap it could easily hit the 22 second range. Too unpredictable for actual race use though.

Next up was a reference run of 10 laps with Feuerdog's downforce tune, although I kept the 40/60 LSD. Easy to drive, but a bit "flat" in my opinion. Rear end lost traction under fast trail braking. Time: 1:23.9. I prefer a more "dynamic" or "flexible" feel, so I went back to my tune. 1:23.4 again.

Final tune
Tires: 28/28
Gears: 3.50 FD, individual gears as specified in the first post.
Alignment: -0.8/-0.7; +0.1/0.0; 5.0
Anti Roll Bars: 12/20
Springs: 350/500; lowest
Dampers: 5.0/7.0; 2.5/3.5
Aero: ---/100 (lbs)
Brakes: 52/100
Differential: 40/60

Edit: new best time after 5 laps - 1:23.046

[TheJohnNewton]

Ske, Nice writeup of your step by step tuning saying what the problem was and what you did to fix it.  Now if only I wasn't alergic to Porsches.