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CARS The Porsche 991 GT3 R

Discussion in 'ACC Blog' started by Aristotelis, Jun 24, 2019.

  1. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    The Porsche 911 has always been a top competitor through the years. The unorthodox architecture with the engine hanging at the rear giving heavy rear weight distribution combined with the short wheelbase, has always been judged as extremely unstable for street use. Yet, in the hands of an experienced professional driver, the extremely fast turn in, the agility in changing direction and the best in class traction, always delivered top performance. Sure everybody would complain of instability at turn in and terminal power on understeer at corner exit. Still professional drivers knew how to deal with such characteristics and adjust their driving style to make good use of the advantages. In a class where the cars were heavy and grip was generally lacking, being able to put the power down and change direction quickly was always an important advantage.
    The choice of the word “was” is not casual though. Modern GT racing have brought to the grid cars with big aerodynamic improvements, electronic systems for traction control and ABS are adjusting traction and grip circles and modern tyres provide more grip. Speaking of which, because GT3 racing is “client racing”, in order to keep costs low, the tyres are identical for all cars with tiny dimension changes.
    The end result is that the Porsche ended up without being able to make a difference with its architectural advantages, while it become even more unbalanced from the tyre dimension availability that often keeps the front tyres out of the operation range.

    Aerodynamic advancements are also limited by the architecture. Much of the aerodynamic downforce gains are made from a big rear diffuser that has to be wide and deep enough. Unfortunately for the Porsche, that’s exactly where the engine sits, so the actual diffuser is very shallow and short. That means the engineers have to work a lot on the front splitter and the rear wing. They manage to create substantial downforce, but it is still not enough. It also generates a lot of drag as it needs the rear wing to work in high angles and most importantly, the resulting aero platform has a very narrow window of operation and a very non linear downforce production that creates unpredictable results. In the paddock, you can often hear the drivers complain that the car works strangely whatever the try to do and the engineers complain that they can make the car “work” in a given circuit or condition. As if things couldn’t get worse, most of the cars have their fuel tank near to their Center of Gravity, so that the fuel load only affects the weight of the car but not the overall balance and handling. Not the Porsche; 120 litres of fuel hanging under the front bonnet. Which means that even if you manage to make the car work with a good setup, the whole balance is going to change when the fuel load will change. The car needs quite different setups for race and qualifying sessions. Often teams will add more fuel during qualifying, to help the drivers with a more predictable handling. During the race, the car will change handling characteristics and the drivers must be ready for it. It’s not uncommon to see the car being competitive during one part of a stint, and then get slower for the rest of the same stint as the fuel load changes, or vice versa, depending on the setup compromise the team opted for.

    Another limiting factor is the engine. This amazing powertrain screams up to 9000 rpm and it is one of the most praised engines in the road car. So how this can be a problem?
    Even though the BoP is not very restrictive, it still has to limit the power to around 500bhp, similar value to the other small frontal area cars. Incidentally this is the same outcome of the street engine. Surely race engines could go higher, but when you start analysing the engine capacity, you realise that there’s not much margin available. The flat 6 engine is normally aspirated and has “only” 4 litres capacity. The smallest engine of the grid is the one of the Honda NSX, 3.5lt but twin turbo. All the other normal aspirated engines vary from 5.2lt V10 of the Lamborghini and Audi, up to the massive 6.0lt V12 of the Aston Martin and the gargantuan 6.2lt V8 Mercedes. Which means that those cars can generate similar amount of power but also massive torque from very low revs. The Porsche engine has to climb up to 9000rpm to achieve the same power and obviously the power band is more peaky. Surely the gearbox ratios can cover the problem, but then again the GT3 series demands a single gearbox ratios homologation that then is used on all the circuits. Some serious compromises must be taken.

    Seems like the Porsche has serious disadvantages and predictably the performance of the car was not adeguate of the name in 2018, with the occasional spark under wet conditions where the traction can make a difference and the top speed is not so important. Porsche focused its efforts on the WEC GTE 991 RSR car which was highly modified with the engine rotated by 180° and practically transformed in a mid engined architecture. The car performed much better and surely the engineers learned a lot from that experience. The 2019 Porsche GT3 R car already won the Monza race and is looking good for the rest of the season. So if you want to win with the Porsche, you need to be a bit patient until we release the 2019 version of the car.

    Still, all said and done, when you get to drive the Porsche, the shortest wheelbase of the grid, the scream of the flat 6 at over 9000rpm, the amazing turn in, while the rear starts to rotate, the fast and constant workout needed with the steering wheel to keep the car from over-rotating and the sublime lightness of the front end when you put all the power down and the front raises up, makes you forget the shortcomings in performance. The car keeps you alive and alerted at any moment. Brings back memories of vintage racing cars when the driver could make all the difference. When finally you manage to drive it properly the level of self reward reaches new heights.
    Forget about top speed, you know you’ll be the slowest anyway. Add rear wing to get downforce, stiffen the rear end to make it rotate, play with the brake bias that can be set way to the rear and start working that steering wheel. The Porsche won’t forgive lazy drivers, it won’t make it easy for you. It demands your total dedication, yes even if you have to race it for 24 hours and doesn’t care if you’re tired. Show the respect it asks for, and you’ll get a different kind of reward that only special cars can give; and if it rains… you might even have a chance for something special.

    Screenshot by user @Tino66 https://www.assettocorsa.net/forum/...-screenshot-thread.50945/page-22#post-1055689
    6-1.jpg
     

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  3. trutya

    trutya Simracer

    very nice and interesting writing! thanks :)
     
  4. The most challenging car.
    Thank you!
     
  5. SimGuy_1

    SimGuy_1 Alien

    YES YES YES! I've looking forward for this post
    THANK YOU !
    Edit:After reading this post no wonder this car is not the fastest around any track i've tried....sigh.
    Blancpain Gt series should allow different tyres for different cars thats only fair besides they gonna reduce bhp for safety reasons (which is a shame)so providing more tyre options is absolutely necessary.
     
    Last edited: Jun 24, 2019
  6. James P

    James P Simracer

    Nice to have you back doing these Aris.

    As you say, you are never going to win on pure pace with the Porsche, but you dont care about that when driving it... its a fantastic challenge

    A quick question, do you know what the main changes are to the 2019 GT3 R car to make it that much more competitive over its older counterpart?
     
  7. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    Yes, the front suspension is totally different, (actually a double wishbone now instead of a strut) and they've manage to push the engine a bit forward. The aero is improved and also a bit less ride height sensitive (the 2018 has some crazy curves, which is one of the reasons the car is so difficult to setup)
     
  8. fabT

    fabT Alien

    This car is all wrong.

    I love it.
     
    NoobJunglerGG, Goony8, th3o and 2 others like this.
  9. SimGuy_1

    SimGuy_1 Alien

    Nice i've noticed from pictures that rear diffuser is better in 2019 compared to current car.
    Can't wait to try 2019 version.
     
  10. James P

    James P Simracer

    Thats interesting, by pushing the engine forward i presume that helps with increasing rear downforce (better diffuser) better weight distribution and keeping all the weight within the wheelbase of the car?

    With the suspension changes, is the aim to keep the front end much stiffer to produce a more stable aero platform under braking? (Front splitter etc?

    Its great to learn about this, thank you for being so open.
     
  11. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    Yes


    Haven't checked the exact geometry yet, but I can safely assume that it will certainly have a much better camber gain that will help the car work with less static camber at front and make the tyres work better that way. I'm sure it also provides better rolling centers control and such
     
  12. [ATF]Shanti

    [ATF]Shanti Simracer

    Once again you hit the point, aris thanks a lot!
    Reading this and remember the 24h in the green hell this weekend raise my respect of those who can handle this Diva even more...
     
    Soldier_003 likes this.
  13. A-Jin

    A-Jin Gamer

    last year this car finished 1st in 24H and this year it finished 2nd massive respect.I think tyre rules are bit different at 24H nurburging to help different cars like porsche.
     
  14. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    Also different BoP.
    Also last year 24h nurburgring, was the first appearance of the 2019 EVO car in any competition.
     
  15. A-Jin

    A-Jin Gamer

    Great Post @Aristotelis.I agree that this car have little on power understeer but it has enough power to get back end out infact i find it more oversteery on slow 1st,2nd and even slow 3rd gear turns.
     
  16. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    Because obviously to be more effective it is using setup that "help" rotating on gas.
     
    A-Jin likes this.
  17. A-Jin

    A-Jin Gamer

    So in 24H nurburgring that car has better compromise than blancpain series? infact this exact 2018 model porsche set fastest lap in 2018 24H nurburgring-->>
     
    Ralph Casey Miller and rich1e I like this.
  18. Coanda

    Coanda Alien

    Legend Aris :cool:
     
  19. James P

    James P Simracer

    Brilliant info Aris, thank you. As others have mentioned, the Blancpain BOP seems to be the toughest on the Porsche compared to other series.

    Really looking forward to you getting in depth with the remaining car blogs such as the Mercedes and Aston :)
     
    f1200racer and Chriss like this.
  20. Chriss

    Chriss Racer

    I find it important to note that the mentioned performance disadvantage is only true for the Blancpain GT3 class and BoP for this car.

    Sports car magazines regularly review the street-legal "basis" of this car (991 GT3 R) with very capable drivers (e.g. Gebhardt). Here, the 991 GT3 R normally wins by miles in track laptime against competitors. I've checked the laptimes e.g. against Nissan GTR, BMW M4 GTS, BMW M6, AMG GT, Aston Martin Vantage, Bentley Continental GT, Audi R8 and for all these, the Porsche was faster. McLaren 650s and Ferrari 488 Pista are competitive or faster, though.

    So, the conclusion is rather that the "basis" of the 911 GT3 is actually very capable with extremely good chassis, extremely good steering, extremely subtle power output. In the corsett of Blancpain GT3 regulations with the mentioned tyre dimension restrictions and so on, it becomes a "just competitive" type of car.
     
  21. Aristotelis

    Aristotelis Will it drift? Staff Member KS Dev Team

    As I wrote in the initial post, the rear weight balance shines where the grip is relatively low and the aero is not that high. Road cars have relatively low grip and no big diffusers
     

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