In the summer of 2022, I drove the Brabus 820, based on the 992.1-generation 911 Turbo S. It proved to be hypercar fast both away from the line and accelerating from a rolling start, and I felt just short of uncomfortable with the g-forces it generated. Fast forward, and the also 992.1 Turbo S-based Brabus Rocket R 900 “1 of 25” Limited Edition made me feel seriously uncomfortable during a full-bore launch on grippy tarmac.
The automotive equivalent of aviators’ G-LOC (G-force Induced Loss of Consciousness) is something I have never experienced before in almost 40 years of performance vehicle testing, even with the likes of a 1,001-horsepower Bugatti Veyron, and it was not a pleasant sensation. It was like a small gravity bomb had gone off inside my skull through first and second gears as the four fat rubber contact patches did their best to rip the tarmac away from Mother Earth. For a couple of seconds, my brain was both shaken and stirred!
Today’s frontline jet fighters like the F-16 and F-35 are designed to pull nine Gs in combat maneuvering. Still, the actual real-world limitation is the pilot’s ability to resist blacking out as blood drains away from the head under high g-forces. This is where training and a G-suit come into their own. G-forces acting on the driver is also an issue with modern racing cars. With high downforce, an integral part of the performance envelope that defines Formula One and Le Mans LMP cars, accelerating at over two Gs, cornering at three-and-a-half Gs, and braking at five Gs over race distance is very punishing to the human body.
A more reclined seating position partly mitigates blood draining from the head. Thus, an F-16 pilot sits fairly reclined compared to previous generation fighters. And if you have the opportunity to sit in a modern Formula One car, you will be surprised to find that the seat is tilted back at nearly 30 degrees.
One of the reasons the Porsche 911 has always been the go-to daily driver sportscar for many is its sheer practicality. Apart from its ability to carry some luggage in the frunk and on the folded down rear seats (not GT models), you get in and out of a 911 like a regular car, mostly avoiding the contortions required with ultra-low, exotic machinery.
While the Porsche’s relatively normal upright seating position is very comfortable and allows you a much better view of your surroundings in traffic, it also means that hard acceleration and braking forces act on your body at almost exactly 90 degrees to the longitudinal axis. Thanks to the weight of its rear-mounted engine, a rear-driven 911 has superior traction off the line compared to a front-engine rear-drive car, and an all-wheel-drive 911 simply has every advantage.
A big issue in an optimum launch situation is the balance between traction and slip. In launching an early rear-driven 930-generation 911 Turbo, a modicum of wheelspin as you depart the line lets you avoid the clutch spin situation that does the drivetrain no favors. However, not all all-wheel-drive 911s are born equal, and the 992 Turbo S is the fastest accelerating 911 variant ever away from the line. Thanks to its near-perfect mechanical and electronic pairing of engine, gearbox, and the front and rear differentials, optimum acceleration off the line and from a rolling start is a given.
Brabus’ chief technology officer, Jörn Gander, explained how the indecently rapid Brabus 820 I drove in the summer of 2022 had morphed into the Rocket R 900. “While the changes made to ramp up the air and fuel demands of the larger turbochargers to reach a reliable 820 hp were a significant jump from the stock 650 hp, finding an additional 80 hp was more of an incremental process,” he said.
Since the 1980s, Brabus has been a master of increased displacement engines, and their first thought was to bore and stroke the 3.7-liter flat-six engine to 4.1 liters for the 900-hp conversion. However, the small volume of potential sales versus the sky-high development costs did not make sense given the likely two-year remaining shelf life of the 992.1 Turbo S on which the Brabus car is based.
The rational alternative was to concentrate on improving efficiency by further refining the turbochargers, increasing boost pressure, and optimizing the control software for both the engine and the PDK gearbox up and downshift protocols within the closed loop system. With nearly 50 years of expertise in forced aspiration, Brabus were well placed to re-engineer the variable turbine geometry (VTG) turbochargers completely
The pair of bespoke Brabus VTG turbochargers used for the 820 hp conversion feature larger compressor and turbine wheels within modified housings. To find the additional 80 hp, the engineers focused on optimizing the profiles and geometry of the turbine and compressor blades for greater efficiency. In the end, not one turbocharger component from turbine wheel to uprated bearings was left untouched.
Back pressure was reduced in the post-combustion stage with a tailored Inconel exhaust system for low weight and efficient heat transfer. Incorporating the mandatory particulate filter, this helps to eke out the last few horses while delivering a more rousing soundtrack. Working with the factory exhaust valve control system gives you the choice of town-friendly ‘Coming Home’ or open road ‘Sport’ modes.
In the old days, engineers used a suck it and see process, but with today’s state-of-the-art computers and test equipment, the development process is both much faster and more accurate. However, even major manufacturers work with the research departments of major universities for some highly specialized areas of engineering, and it is not uncommon for Graduate, Masters, and PhD students to end up joining these very companies after their time in academia.
Brabus has a good working relationship with the Engineering Department at Heidelberg University and once again called on them for help with the Rocket R 900 project. The cutting-edge Computational Fluid Dynamics equipment in the faculty can accurately predict airflow in and out of a given engine during the combustion process.
In this case, the required target output of 900 hp pointed towards the need for a 1.0 mm (0.04 in.) increase in turbo compressor wheel diameter along with a slightly revised blade geometry. Once the new components were created and installed in the modified turbocharger housing, the electronic control unit software was adapted to maximize the optimized airflow capability. The power increase Brabus was looking for showed up on the engine dyno printout, and on 1.9 bar (27.5 psi) of boost the 3.7-liter flat-six makes 900 hp at 7,200 rpm and 737 lb-ft of torque at 5,100 rpm.
“To make full use of the extra 80 hp, we set out to fine-tune the way the drivetrain responds by carefully calibrating the gearbox and clutch control software to the revised power and torque curves,” Gander explained. “The 900 hp arrives at 7,200 rpm, compared to the factory stock 650 hp at 6,750 rpm. The PDK gearbox is mechanically strong enough to handle the extra output, and we increased the clutch clamping pressure to handle the extra power and torque and prevent the clutches spinning during a full-bore launch on a grippy surface.”
Our test instruments recorded 2.5 seconds for the 0-62 mph sprint, with 125 mph coming up in just 7.2 seconds. Top speed is electronically limited to 211 mph due to the speed rating of the tires. While some other very quick cars might equal these initial acceleration numbers, it was the sheer g-forces imposed by the lack of tire slip when using the Launch Control that delivered the aforementioned uncomfortable few seconds.
Form definitely follows function here in the way the wind tunnel developed aerodynamics have been parlayed into a unique and distinctive Brabus house style that the Porsche world has never seen the likes of before. The thuggish looks and low, wide stance give the car immense gravitas, and the first time you lay eyes on it, you know there is something serious going on.
Jörn Gander explained that the Rocket R 900’s aerodynamic development proved to be one of the most demanding projects Brabus has ever undertaken. The wind-tunnel optimized Brabus Widestar carbon-fiber suit of clothes presents a greater frontal area to the air molecules than the factory fresh Turbo S. As well as moving the center of pressure aft, the greater downforce created by the much larger carbon-fiber front spoiler produces a better overall aerodynamic balance for the tail-heavy Turbo S, changing the downforce ratio from the stock 80 percent at the rear to a more even 60 percent.
Behind the large front air intakes, new pipework channels air into the factory radiators, as well as the ceramic composite brakes. Bespoke carbon-fiber wheel arch liners with wind-tunnel derived vents pair with the distinctive alloy wheels to smooth airflow in the front wheel housings, speeding up its exit to enhance laminar flow past the doors into the large rear arch intakes feeding the intercoolers.
“We spent a lot of time on airflow management in the front wheel housings, and this alone took five days of work in the wind tunnel at the Toyota Gazoo Racing facility in Cologne,” Gander recalled. Ride height plays a big part in aerodynamics as the car itself is actually the biggest spoiler of all if you think about it. The expert here is an ex-Dallara engineer who helped Brabus optimize the final set-up for their coil-over suspension, which works in conjunction with the factory Porsche Active Suspension Management and front-lift systems.
The prominent carbon-fiber front spoiler that uses the factory mechanism to lower itself further into the airstream at speed is matched at the rear by an integrated spoiler inspired by the unique arrangement first seen on the Group 5 Martini 911 2.8 RSR that debuted at the Monza 1,000 km race in 1973.
On that first outing, the RSR had makeshift aluminum spoiler panels riveted to the bodywork on either side of the ducktail spoiler, these additional winglets giving rise to the ‘Mary Stuart collar’ nickname. By the time the Le Mans 24 Hours came around in June, this wrap-around spoiler had been properly integrated into wider rear wheel arches.
Taking its design cues from the Group 5 RSR, the Brabus rear spoiler, topped off by a carbon-fiber Gurney flap, rises and tilts to produce similar downforce to the extendable rear wing on the stock Turbo S. Meanwhile, the extendable race style carbon-fiber front spoiler makes significantly more downforce than the factory chin spoiler.
The wider wheel arches of the Rocket R 900 cover a set of 9.5J x 21 and 12J x 22-inch diameter Brabus Monoblock P forged alloys wrapped in 255/45ZR21 and 335/45ZR22 Continental Sport Contact 7 rubber. Tailor-made with unique offsets just for this car, these wheels feature carbon-fiber Aerodisks designed to help clean up the airflow, while their peripheral slots extract heat coming off the huge brakes when they are being used hard.
When fully unleashed, the Brabus Rocket R 900 is a controlled explosion on four wheels with more than enough go to match its extrovert show. However, it also has a softer side that allows you to cruise around town like the stock car. Consider it a Turbo S with the dial turned up to 12.
