With substantially increased straight line speed and down-force, the 2015 919-Hybrid showed just how big a stride Porsche has made from their 2014 car at both the Silverstone and Spa rounds.Beginning with the chassis, Porsche carried over its two-piece bonded chassis from the 2014 WEC season. The design was fairly outdated and allowed the car too much movement; flexing an estimated 0.01 of a millimetre.  For 2015, Porsche knew performance could be gained here, so consequently switched to a one-piece monocoque. This therefore meant Porsche saved a lot in weight, with additional help from Capricorn Composite GmbH (of which Porsche bought a 25% stake this year) who changed the weave of the Carbon for added stiffness with less being used up in the process. Revisions were also made to the engine block to aid installation stiffness as it is a semi-stressed member, in addition to the tub changes.
For the Suspension, Porsche had much discussion on where to go given Audi went for Front-rear interconnected system. It’s still unsure what Porsche run now, although it’s a well-adapted FRIC system (to minimise pitch and roll) is in development for the car. The most recent monocoque has led to the new design which Porsche Technical Director Alex Hitzinger was very pleased about. Speaking to Alex earlier about the Audi system, Porsche tested an FRIC last year, but Alex ditched it for being too heavy and complex. They now have a clever mono-shock front arrangement.
In 2014, Porsche ran a very unique self-levelling suspension design, which featured a levelling cylinder and spring connected to the top of the gearbox and control arm ends. It will neutralise any off balance that you would get with conventional springs.
At Spa and Le Mans last year Porsche had an actuator failure, so means the system is temperamental. It’s still unsure whether Porsche will be running this, but most likely will be a re-designed concept. This year Porsche still have the conventional Push rod all round with double Aluminium wishbones too.
Next we have the new power train of the 919. Porsche had a lot of issues with the 2014 car; suffering from extensive vibration from the V4 two-litre engine. Porsche have modified the engine firing order as well as implementing a refined crankshaft. Furthermore new con-rods, pistons and crank case have all been adjusted to suit the new engine. With new changes to the turbocharger and its ballistic cover has resulted in less lag.In addition Porsche has updated its compressor and turbine technology with a view to reducing the amount of moving parts. The exhaust layout is same to last year, which is used as an Aerodynamic benefit. The manifold and pipes emerge from each bank of cylinders to combine into single pipe – a design which worked very well on the Mercedes W05 F1 car.  This forms a collector where the gases exit together, which on the Porsche is very early as the pipe exits the cylinder bank. Each pipe rotates 180° to a single pipe. The layout splits again into the right hand of the car through the turbocharger, or left through the MGU-H (Motor Generator Unit – Heat) Which Porsche used last year as its ERS (Energy Recovery System) and same this year.
While this design is used by all current Formula 1 teams, what’s clever about the engine is that Porsche are able to continue running even if the ERS unit fails by very cleverly running a turbocharger Wastegate so the V4 engine is able to keep working. If this design was implemented in 2014, Mark Webber may have gone on to win Le Mans. It is not the same as F1 units. The ERS part is completely separate from the turbo-charger. The level of ERX is controlled by a variable geometry turbine on the MGH-H, while the turbo has a fixed geometry. For this year, working with Garrett they revised the geometries of each of both of these. The reason behind the choice of having a separate MHU-H is one of redundancy. If it packs up, it can just be bypassed).
While Porsche continue to run the V4 engine, it still has the single turbocharger with four valves per cylinder and direct injection. Its again 90° mounted. The transmission is rear-wheel-drive with a 7 speed sequential racing gearbox. The car can also be all-wheel-drive when the front ERS is deployed. The ICE (Internal Combustion Engine) is reported to produce over 500BHP, although the car looked a lot faster than that – most likely due to their impressive Hybrid system upgrade. It also got a bit larger, with a slight increase in stroke. Boost and CR also went up.
The Hybrid system has come on leaps and bounds from 2014. It has been a big talking point this year, as Porsche will run 8MJ (Mega Joule) although only at Le Mans, all the other circuits of the WEC will be less by regulation. Lots of development has gone into the all new battery system so that the car can take on-board the full 8MJ amount. Porsche’s ERS is mounted onto the front axle of the car with a reported 400BHP output. ERS is also taken from the exhaust gases at the rear for the turbocharger. The energy is stored in liquid-cooled Lithium ion (LI) batteries which were in special development from A123 systems. The batteries are actually developed in house by Porsche. A123 supply the individual cells, but the battery architecture, BMS etc are all Porsche developed.
Looking at the Aerodynamics, Porsche is opting for its traditional low down-force philosophy. What the Weissach crew has done is re-design the nose cone structure to a much lower profile. The most likely reason being the low nose would allow as much airflow to pass over the car as cleanly as possible; thereby reducing its footprint as it cuts through the air. Apart from the new nose configuration the car remains similar to the car of 2014.With the splitter being right at the front of the car it’s important to feed it as much air as possible. This will give the overall car more down-force. The rear diffuser and the under body will have a cleaner flow to work on, and so can produce more with the same amount. On the side pods, Porsche have new side louvres on the 919; where the air flow exits the car as it enters under the nose cone, just below the splitter.
While this isn’t exactly new, Porsche have refined the aero through extensive hours of CFD (Computational Fluid Dynamics) and Wind Tunnel testing, with velocity streamlines highlighting any corrupt air flow. For Le Mans Porsche have added a curved section to the central section of the splitter, so that the car will produce a cleaner flow under the car, resulting in less drag.
Right at the rear of the car, Porsche have a new engine cover. They have trimmed the rear bodywork to create some extra down-force supplied by the rear cover lip at the trailing edge. Alex Hitzinger claims the under floor also has new winglets for more stability through high speed cornering.
Porsche will also run its exhaust gases into its rear wing main-plane. This concept was used in the classic days of Formula One and Porsche has exploited the blown diffuser effect and benefit well, with all drivers pleased with the improvements of the second generation 919.