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911 GT2 RS – Designing for the road, delivering on the track

Bringing out the new 911 GT2 RS, the Porsche motorsport division has revealed the fastest, most powerful, road-legal 911 of all time. On the 20th of September 2017, this phenomenal supercar achieved a road car lap-record at Nürburgring Nordschleife with Porsche’s test-driver Lars Kern on the steering wheel and 6’ 47.3” on the clock.

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The 700 bhp delivered by two turbos and 6 flat cylinders, catapult the 1,470kg coupe to 100km/h in 2.8 seconds, while 8.3 seconds later the speedo needle crosses the 200km/h notch, before it finally settles at 340km/h.

To put it into perspective, at that speed it would take just over 33 minutes to complete one rotation of the 188km-long M25 or a mere 3.6 hours to cross France, from Calais to Nice.

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The 3.8lt engine is no stranger. Since 2009, it has been compressing air via two variable geometry turbos.

These are designed to adjust to the air flow characteristics and were first used on an internal combustion engine by Porsche. But now, the power increase achieved is of the order of 40%, compared to the 500bhp delivered by the respectable 911 turbo.

An additional comparison of the GT2RS, this time to the previous 3.6lt GT2, reveals an increase of 80bhp in power output and an additional 50Nm in torque. The lingering question is how?

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With many modifications to the 580bhp motor occupying the Turbo S engine bay. Is it enough? Well, no…

The engineers had to come up with innovative ideas, some of which are quite straightforward in their concept. They do, however, bring about a series of significant alterations and thus the need for further investigation.

Bigger turbos compress more air into the combustion chamber and this increases the rate at which energy is transformed, something which is increasingly important at high speeds, when the corresponding gas cycles are extremely short. However, at the same time, certain pistons have a reduced compression ratio by 0.5.

What happens to the dynamics of the engine (oscillations) and how the engineers manage to balance their monstrous creation, is something they don’t care to share.

Another very interesting design feature is that of the air intake. Traditionally, the intake air is further compressed by the oscillations (vibrations) of the intake valves. This intake system is longer and of smaller diameter, with short intake ducts to the cylinders. This way, the fuel/air mixture is diffused and thus cooled. The corresponding benefit from the efficient mixture management reflects to both the performance and the economy.

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Undoubtedly, one of the most impressive engineering principles applied on the 911GT2RS is in fact common practice in designing motorsport cars.

At times of high thermal loads, the compressed air is cooled by spraying water on the heat-exchangers. The air temperature drop at high compression is an astonishing 20°C more than that resulting from air-flow (convection) cooling. This magnitude of temperature drop ensures thermal uniformity and stability in the air-flow even when the car is driven to its operational ceiling. When among other parameters, the intake temperature is higher than 50°C, the driver suddenly releases the accelerator by more than 90% and at the same time the engine operates at more than 3,000rpm, a pressurized distilled water system is activated, channeling the cooling agent from the tank into the sprinklers. This partly explains the lap-times at Nürburgring Nordschleife, with maximum power delivery at all parts of the track, even on a hot day.

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In order to utilize all this available power, a worthy chassis, correct adjustments and focus on weight reduction, are all vital elements.

The chassis employs universal joints exclusively, something that Porsche decides for the first time on a road-car. The feeling of rolling and the dynamics developed are continually and precisely transferred to the driver, throughout the operation envelope of the 911GT2RS.

The engine is supported by dynamic mounts, which are adjusted accordingly. When the driving conditions are “normal” a soft setting allows for comfort, restricting unwanted vibrations. However, since driving a 911GT2RS can quickly become a “paranormal” experience, at full throttle the mounts “tighten-up” and the result is the immediate and uniform acceleration, without the vertical oscillations, which affect traction on the rear axle.

The “Weissach package” is what describes the body of the GT2RS in two words. It bears the name of the Porsche facilities (including a track), worthy of a visit for a unique driving experience.

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The “Weissach” (pron. vaee-zah) eliminates 30kg making extensive use of carbon-fibre and titanium. The roof, the tie-rod ends and the anti-roll bars are all made of CF.

The magnesium alloys reduce the total weight, as well as the “unsprung mass”. This refers to the weight that is “hanging” and includes the wheels, brakes, suspension, steering and it is a very important factor in the total dynamic design of a race-car. And that is what the GT2RS truly is…

The traction control and dynamic suspension systems are what one might expect from the Porsche Motorsport division. The same goes for the technologies aiming at the passengers’ comfort and visual satisfaction, although the elaborate racing styling attempts to differentiate this 911 and elevate the overall optical experience to that of advanced supercars with racing credentials.

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Much like the rest of the assembly, the interior is a harmonious amalgamation of elements, worlds apart one from the other. The standard 911 centre console “adjusts” to the racing cabin atmosphere, dominated by the carbon-fibre bucket seats.

The epilogue of the Porsche 911GT2RS is a difficult one, balancing between road and race track, trying not to understate the first and not to overstate the obvious. It will suffice to use the phrase from Porsche that “it is the only road car capable of instilling a race car sensation”. An unexpectedly short phrase, backed however, by a long list of credentials.

 

 

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