Modified 911s part 2: water-cooled
Once a 997 Turbo, this 1,000bhp behemoth has been developed to dominate Extreme Supercar racing in South Africa
Think you see a 997 Cup car? Think again. Johann Venter has the full story from the track in South Africa
The directive was clear: to build one of the strongest and fastest circuitracing Porsche in the world. So states Cobus Jonker, chief engineer and team manager at Scribante Racing. Team principal and driver Franco Scribante defines the reasoning behind this extreme 911 GT3 R: “While campaigning our Chevron B26 at the International Kyalami Raceway Motoring Show Festival, we realised we needed to liven up our game! Nothing at the time seemed more exciting than the G&H Transport Extreme Supercars. Top-end cars going wheel-to-wheel in an exhilarating nineround national championship. We just needed the right weapon to do battle at the sharp end of this tightly contested championship.” Thus the Scribante Racing’s 1,000bhp version of the 2013 Porsche GT3 R was born – developed within just seven months.
It is a sight to behold, its dark-grey matte paint finish and piercing yellow LED headlights giving it a real menacing look. There is so much to take in! So let’s get better acquainted with this spectacular track thoroughbred. The chassis is a 2008 997.2 Turbo. Its GT3 R kit was imported from Weissach, comprising of carbon fibre fenders, front bumper, rear bumper with integrated spoiler and diffuser, side skirts, doors, rear quarter panel, engine lid and wing. “The biggest challenge was to adapt the kit, which was designed for a normally aspirated car, and make it work for our Turbo setup,” explains Cobus. He continues: “No provision was made for the intercoolers, everything was sealed on the rear arches. The entire rear quarter had to be redesigned and modified to accommodate the intercoolers, as well as the intakes and outlets. In fact, most of the kit had to be modified to suit our purposes. The intake ducting for the turbos also posed a massive obstacle. Eventually we decided to place it at the rear of the cabin so that air is being sucked in through the rear windows, creating much better airflow with cleaner, cooler air, as opposed to
the pipe being crammed into the engine bay where temperatures are much higher.
“To develop the air ducts in the rear arches custom 3D scans were made; the air ducts were then designed in Solidworks, where airflow was simulated to ensure the air duct would offer the least amount of drag.” The car does, however, look significantly different from the GT3 R launched in 2013. “Our car does incorporate some of the upgrades brought about with the 2016 car,” Cobus says. “We’ve fitted the big slanted radiator up front, instead of three radiators which increase weight and drag. The front aluminium lid was custom designed in-house to incorporate slats, which suck air through to create better downforce and less drag. We also improved on the overall aero package, making the car as streamlined as possible. Just look at the mirrors – designed internally to guide air away from the rear wing.
“There was no blueprint for this build, none of the components used are off-the-shelf. We sourced them from highly specialised suppliers, and even then had to modify them to suit our purpose… many parts were designed and made in-house. We even used a supplier that makes helicopter screens from polycarbonate to make all our windows.” However, he’s not keen on mentioning suppliers, but in the dark art of Extreme Supercar racing, I can’t blame him.
I am keen, however, to find out what lurks underneath and manages to push out 1,000bhp.
Cobus indulges us: “We brought in an engine from the US, based on the M97 unit – it’s been developed for racing and its displacement increased to 4.1 litres. Internally we substantially re-engineered it to cope with the strain of 1,000bhp and to accommodate higher boost pressure so we can compete from the front. The sleeves and camshafts were coated with a special DLC coating to reduce friction and wear.
The motor uses specialised, lightweight pistons, connecting rods, billet crank, cast-iron sleeves, extended valves, billet intake manifold and rather aggressive billet camshafts.
“We installed a modified internal oil pump and custom head gaskets with Garlock and Inconel O-ring seals,” Cobus continues. “It is equipped with 1,700cc injectors per cylinder and a larger throttle body. The exhaust and manifold were made in-house, and the turbos were imported from the US. Each turbo has a super core with billet-extended blade compressor wheels. To get the boost pressure equal per cylinder bank, one turbo uses reverse flow; each rated to 750bhp. The boost range is from 0.8 bar to 1.4 bar and is controlled by map rotary switches on the steering wheel, although each turbo is capable of boosting 3.5 bar.
“To keep temperatures under control a waterinjection system is used to spray a fine mist of distilled water on to the radiators.” How is all that power transferred to the wheels? Cobus answers: “We had difficulty finding a gearbox that could handle the 1,000bhp power level. We eventually sourced a fully sequential, pneumatic, six-speed dog-type ‘box from Australia. We use a MOTEC paddle shift kit, which consists of an air compressor and accumulator. All the internals of the gearbox were cryogenically treated and REM ISF micro polished: the aim was to have it as light and compact as possible, yet able to deal with the tremendous power… it weighs a mere 63kg,” he states. “The crown wheel and pinion are normally the weakest link on these transmissions, so a stronger final drive was designed to reduce the amount of flex, with carefully matched gear ratios.
It is fitted with a triple-plate Tilton clutch, rated at 1,800Nm, and a floor-mounted 660 pedal assembly.”
It must take some doing keeping all of this momentum within the confines of the race track? “Yes,” he acknowledges. “That’s why we developed our own unique suspension and brake set up.” It’s made up of GT3 R uprights with GT3 Cup cross members, a 997 Turbo steering rack and Penske racing dampers. The suspension components are primarily cast iron and chrome-moly, which include
roll bars, wishbones and downlinks. The brake callipers and discs are 2017 FIA GT3 approved: AP Racing Monobloc Aluminium alloy, six pod calipers in the front (316mm in length) and four pod at the back (275mm in length), with a M4 Motorsport Bosch ABS unit. The discs are floating ventilated AP Racing discs: 378mm in diameter and 36mm thick in the front, 355mm in diameter and 32mm thick at the rear. Never before has such a sizable caliper been used on a Porsche for a racing application. The arc of the rim is therefore very aggressive, these are custom-made by AG Wheels in the US. It has a full billet centre, forged outers and all bolts, nuts and drive pins are made from titanium. These are 13-inches wide at the back, 12-inches in the front (18 in diameter), fitted with slick Pirelli P Zero medium compound tyres.
The nerve centre is the multi-function steering, designed in-house to incorporate a MOTEC C125 display. It shows a plethora of readouts and, together with the keypad in the centre console, enables one to pilot this supercar. Speaking of which, it won’t be me partaking in some low-flying laps around Zwartkops Raceway today, however, there is still so much that can be garnered from the car.
Even on the warm-up lap I am astounded by the noise emanating from the back of the GT3 R. Initially it roars like a dragster, then, suddenly, the turbos come on, and the sound transforms into that of a fighter jet at supersonic speed… it is epic! We soon start raising the speed of this ferocious GT3 R. The pace is electric, yet Franco, the driver, makes it look so easy, cutting the perfect racing line around this eight-turn, clockwise circuit.
Each breaking point is perfectly executed, a harmonious balance between down shifts, throttle input and brake feed. There is absolutely no shudder and no need to fight the steering. Franco later tells me that the sheer pace of the car means overtaking is a common part of his task when battling through the field on race days, overtaking on and off the racing line. He shows us some racing footage; the vision and anticipation of movement has to be absolutely first class here, as the GT3 R is simply able to cover ground so quickly. All this while having to be fit enough to cope with the physical demands of piloting this turbocharged weapon. We salute you, Franco!
There seems to be no weak point in the engine: power – stupid amounts of it – seems to be there all the time. Yet the GT3 R is perfectly balanced. It is extremely well-planted with superb handling, which it needs to have to cope with its speed.
However, Cobus says the GT3 R is not yet finished: “The car is still not where we want it to be, but we are definitely getting there – and quickly. Every time we go out on track we are taking huge strides forward, the pace is just getting quicker and quicker. We actually need a solid year of racing to unleash the ultimate performance of this Porsche. We are not a factory team, nor do we have the backing of major sponsors, only a five-man crew comprising of myself, Marco Mendez da Costa (control systems engineer), Eugene Katze (mechanic/fabricator), Edwin Kuppan (mechanic) and Dwain Degenaar (fabricator/spray painter) that has managed to develop a world class, circuit racing Porsche.
“Franco has shown the leadership and conviction to be the best. He has a real hunger to win. Together we achieve more, and achieve big. That’s the secret to our success, really,” answers Cobus. I ask Franco for his overall impression of this incredible project: “We’ve gone through some teething problems, but
I’ve experienced the car at optimum race pace, and on those occasions I have left the competition behind by a country mile. The rewards, however small, have been well worth the agony, trepidation and loss we’ve been through over the last several months.” As the saying goes: nothing ventured, nothing gained… Special thanks to Ron Silke and Zwartkops Raceway for use of the track