In 2014, its second year as a works racer, the Porsche 911 RSR finished second to Ferrari in the FIA WEC Manufacturers title race in the GTE PRO class. Porsche finished behind Ferrari, but ahead of Aston Martin. The Porsches scored two race victories to Ferrari’s four, but the 911s racked up six second places between the two cars, to Ferrari’s single second place. Although it was Ferrari’s name that appeared on the trophy, the 911s could boast an impressive record of consistency.
So what did the engineers back at Weissach get up to over the winter of 2014 to make the RSR into a potential winner in 2015? I spoke to works driver Patrick Pilet and to Dr. Frank-Steffen Walliser, head of Porsche Motorsport, about the 2015 racer that became a Championship winner.
One of the key factors in the development of the 2015 RSR was to improve its ‘drivability.’ Dr. Frank-Steffen Walliser said, “So it was more about how the car behaved under braking, under lift-off, and when you got back on the throttle again, everything to do with the drivability. We focussed on what would give the driver the right feedback to make it easier to handle, so he would know where the car is and whether he had over- or understeer.” By comparison, the front spoiler on the 2015 car was similar to the 2014 model, but the later car has a small raised section in the centre of the front spoiler, allowing some air to flow under the vehicle. This small change means that the level of downforce was not influenced as much when the car lifts off when jumping the curbs.
The drivability factor was of paramount importance, as RSR works driver Patrick Pilet explained, “The 2015 car was more driveable, it was less snappy in the fast corners and it was more efficient.” The instability that the drivers sometimes experienced in the past has gone. The car is now more ‘linear’ as Pilet put it, and is therefore easier to drive as it now sits as opposed to dives under braking. Asked where he felt the biggest difference was, Pilet responded, “Especially on the turn-in on the fast corners because, with the new front that we have, the car is less pointy, or sharp, than before. Sometimes in the initial braking phase we could pick up some instability because we had a small aero difference between the front and the rear.”
Body and Aero
The Endurance Committee of the ACO has the absolute right to modify the Balance of Performance (BoP) between GTE cars through adjusting the weight, engine performance or aerodynamics. With this backdrop, the manufacturers and teams must prepare their cars within the guidelines laid down by the regulations. “The rear wing is exactly the same because it is a homologated part, so you cannot change it. There were only slight evolutions possible, but the rear wing was not affected,” Walliser pointed out.
The 2015 RSR body is still the same steel/aluminium hybrid design which uses the 911 Carrera 4 (991) as the base body, as this was the widest body available in the range at the time the race car was homologated. The regulations for GTE PRO cars state that, “The period of restriction will begin for 2013 models for LM GTE-PRO cars. It will be the same for every car.” This set of rules effectively freezes any major changes, which means that this current 911 RSR had to remain the same for the 2013-2014-2015 seasons. Walliser confirms this, “The new three-year homologation period in GTE starts in 2016, and runs to 2018.”
Chassis and weight distribution
Over the winter the Porsche engineers made some small detail changes to the kinematic points on the front axle, as Walliser explains, “They were able to make some slight adjustments, but this had to be done within the rules of the homologated car, so we could only make small adjustments.” It was through some of these small adjustments, which led to the improved handling of the car. Asked if they were able to improve the car’s weight distribution in any way, he responded, “For sure it is always the aim to be able to adjust this weight distribution, but you cannot make tremendous changes.” The regulated minimum weight for the 911 RSR is 1245kg.
The 911 RSR is powered by the same 4-litre aluminium boxer engine as before. It has a bore of 102.7mm and stroke of 80.4mm giving a capacity of 3996cc, and develops 470hp (345kW) when fitted with a pair of 29.3mm restrictors in accordance with the BoP criteria. The engine operates with 4-valve technology, is water-cooled, has dry sump lubrication and multi-point fuel injection.
It is on this last point, the fuel injection system, that the racing Porsche differs from the road-going model. EFI direct injection was used on the 997 back in 2008, so the technology was available but Porsche have previously said that they won’t develop it for racing until they are satisfied that the rules are stable. Walliser pointed out that, “At the moment this car is homologated with the multipoint injection and not direct injection.” However, the privateer teams have been calling for direct injection, not only because of the increase in power it brings, but for the improved fuel consumption it delivers. When prompted on the question of direct injection for the 2016/2017/2018 seasons, Walliser responded, “We will see. It is not finally decided, it depends a lot on circumstances.”
From the driver’s point of view, Patrick Pilet said this, “We have a really good engine, but we have the smallest engine of the field, a 4-litre unit without turbo. It develops a lot of horsepower if you take into account the air restrictor size and the fuel capacity that we have, so I think the engine is really optimised. Beyond that, it’s all about durability, and to be sure that the engine has no problems for the long 24-hour races.”
Wheels, brakes and suspension
Keeping the 911 RSR on the track are four Michelin racing tyres mounted on BBS alloys. The front 12.5J x 18 wheels are shod with 30/68-18 Michelin rubber, while the rear 14J x 18 wheels are fitted with 31/71-18 tyres. The Brembo brake system comprises 380mm steel discs with six-piston monobloc fixed brake calipers up front and 355mm steel discs with four-piston units, internally-vented, at the rear. The suspension is a fully-adjustable double-wishbone suspension setup at the front with 4-way gas pressure shocks, double coil springs (main and helper) and adjustable blade-type anti-roll bar. At the rear is a multi-link axle, 4-way adjustable shock absorbers, double coil springs (main and helper) and adjustable blade-type anti-roll bar.
Single point refuelling was introduced in 2015 on the 911 RSR, which greatly contributes to safety in the pit lane. The refuelling system utilises one hose for both filling and venting, leaving only one refueller to work on the car. The refuelling hose consists of a two part concentric tube, so when refuelling commences, the fuel flows down the outer tube and air is forced back up the inner tube. “We can take the second guy, who is standing with his back to the pit lane, out of the process and that was a safety issue,” justified Walliser.
For the WEC 2015 season opener at Silverstone on 12 April, the drivers were: #91 – Richard Lietz/Michael Christensen, and #92 – Patrick Pilet/Fred Makowiecki. Between these four drivers they have a total of 21 years of combined service as Porsche works drivers, and while Lietz and Pilet claim the bulk of those years, Fred ‘Mako’ has an impressive record in GT racing that stretches back several years. At 24 years of age, Christensen is the youngest and has spent the least amount of time in a Porsche but if you think he is a lightweight, you would be mistaken, as he has come up through the ranks of the Porsche Junior Driver and Porsche Supercup series.
At Silverstone the lead 911 RSR was almost 7/10ths of a second off the pace of the Aston Martins who had locked out the top three positions on the grid. When asked about the performance gap, Patrick Pilet responded, “Even with the BoP, we know they still have a big power advantage, and especially here you need a lot of torque, and they have lots, but we will see what the pace is during the race. Anyway, we will never give up. We will push harder from the first stint until the last lap, and we will see where we are at the end. But for sure they are strong.”
Although Porsche will not be fielding a 911 RSR entry for the whole WEC season in 2016, they will be supporting the #77 Dempsey-Proton Racing 2016 car in the GTE PRO class in all nine races, with Richard Lietz at the wheel. In the GTE AM class, there will be three Porsches in action for the whole WEC season. Round three of the WEC at Le Mans will see the #77 car joined in the GTE PRO class by the usual #91 and #92 works cars with drivers Patrick Pilet and Fred Mako respectively. The GTE PRO class is going to be fiercely contested with fourteen cars this year, what with the inclusion of a squadron of four Ford GTs. Fourteen cars will also be in action in the GTE AM class with four 911 RSRs entered, including one each from the KCMG, Gulf Racing, Abu Dhabi-Proton Racing and Proton Racing teams. Although ninth on the reserve list, another Porsche 911 GTE AM is waiting in the wings should others withdraw.
One thing is for sure, while Porsche wait for their new 911 racer to be ready for 2017, they will be mighty busy in 2016 with such a full field of private and works cars racing throughout the season. And that means that the spectator is going to be in for a feast of action…so take your seats, buckle up and wait for the starter’s orders!!
Written by: Glen Smale