After a 15-year absence from outright contention Porsche completes a three-pronged manufacturer attack at this weekend’s Le Mans 24 Hour.

With tweaks to the 2014 rules, all three are running different solutions to how they can extract a set amount of energy from the highly complex propulsion systems.

In the two previous lead up World Endurance Championship races at Silverstone and Spa, all three manufacturers have grappled with technical problems of varying forms.

The following is a look at what makes the 2014-spec LMP1s tick.

PORSCHE 919 hybrid

The drive system of the new LMP1 race car is based on a compact, lightweight four-cylinder petrol engine.

The two litre engine spins to 9000rpm and runs a single turbo and direct injection.

It also features two different energy recovery systems.

Fundamentally new is the recovery of thermal energy from exhaust gases.

An electric generator is used here, which is powered by the exhaust gas stream.

The functionality of the second hybrid system is known from the Porsche 918 Spyder.

A generator on the front axle utilises braking phases to convert kinetic energy into electric energy.

It is also stored in highly-advanced liquid-cooled lithium-ion battery packs until the driver needs the extra energy.

Then the front generator is operated as a single electric motor and drives the two front wheels via a differential in the acceleration phases.

This gives the Porsche 919 Hybrid a temporary all-wheel drive system, because the petrol engine directs its power to the rear wheels in a conventional way.

Key points:
*Rules specify four classes of energy levels from 2 to 8 megajoules (MJ)
*The 919 is registered for the 6 megajoule category
*Under this rule it can use 1.67kilowatt hours (kWh) of energy per 13.629km lap at Le Mans
*With the energy the Porsche recuperates during the Le Mans race, it would be possible to cover 4,576km with the most efficient electric car available in the compact road car class – the Volkswagen e-Golf.
*Bound by the 6-MJ class, the rules allow the petrol engine with over 500bhp a consumption of only 4.78litres per lap in Le Mans.

Tech specs:
Class: LMP1
Monocoque: Developed based on LMP 2014 regulations and is tested to comply with the 2014 FIA Crash and Safety Standards.
Engine: V4 with turbocharging, four valves per cylinder, DOHC, one Garrett turbocharger, petrol direct injection, aluminium cylinder crank case fully bearing, dry sump lubrication.
Power (combustion engine): 370kW.
Capacity: 2litres
Hybrid system: KERS with 185kW Motor Generator Unit (MGU) on the front axle, ERS to recover thermal exhaust energy. Storage in liquid cooled lithium ion battery packs (with cells from A123 Systems).
Drive: Rear-wheel-drive, traction control (ASR), on-demand four wheel drive by boost from the e-motor to the front axle, sequential, hydraulically operated seven-gear racing gearbox.
Chassis: Front and rear independent suspension with multi-link, pushrod suspension system and adjustable shock absorbers
Minimum weight: 870 kg
Length: 4650mm
Width: 1900mm
Height: 1050mm
Tank capacity: 66.9litres

TOYOTA TS040

The TS040 hybrid delivers a maximum power boost of more than 18 percent while complying with new regulations that cut fuel use by 25 percent.

Output from the car’s hybrid system has gained well over 100kW to a peak of 736kW by combining a major advance in electric power with a larger capacity 3.7 litre V8 petrol engine.

The system takes hybrid technology to the next level, adding a motor-generator on the front axle in addition to a similar unit at the rear, allowing the system to provide power to all four wheels.

A major evolution of the previous TS030 hybrid that won five WEC races over the past two seasons, the latest powertrain harvests more braking energy that is stored in a super-capacitor and used under acceleration to deliver a 353kW power boost.

Key points:
*The hybrid system delivers a power boost of more than 18 percent and uses 25 percent less fuel.
*Combination of an advanced electric power unit and a larger capacity 3.7 litre V8 petrol engine boosts power by 100kW.
*The system takes hybrid technology to the next level, adding a motor generator on the front axle in addition to a similar unit at the rear, allowing the system to provide power to all four wheels.
*The TS040 powertrain harvests more braking energy that is stored in a super capacitor and used under acceleration.
*TS040 has increased downforce to compensate for 50mm narrower tyres.

Tech Specs
Class: LMP1
Engine: normally aspirated V8
Capacity: 3.7 litre
Fuel: Petrol
Overall power: 736kW (petrol and hybrid)
Hybrid power: 354kW
Length: 4650mm
Width: 1900mm
Height: 1050mm
Capacitor: NISSHINBO
Front Hybrid Motor: AISIN AW
Rear Hybrid Motor: DENSO

AUDI R18 e-tron quattro

Audi is running what it considers the most highly complex technical racecar it has built.

The further developed V6 TDI unit of the Audi R18 e-tron quattro makes a crucial contribution to the car’s compliance with the energy specifications of the regulations.

The new R18 has to do with up to 30 percent less fuel than its immediate predecessor due to the new regulations.

For the first time the powertrain concept features the integration of two hybrid systems.

As in the past, a Motor Generator Unit (MGU), during braking events, recovers kinetic energy at the front axle, which flows into a flywheel energy storage system.

For the first time, the turbocharger of the internal combustion engine is linked to an electrical machine, which makes it possible to convert the thermal energy of the exhaust gas flow into electric energy – for instance when the boost pressure limit has been reached.

This energy also flows into the flywheel energy storage system.

When the car accelerates, the stored energy can either flow back to the MGU at the front axle or to the innovative electric turbocharger, depending on the operating strategy.

The options available to the drivers and engineers as a result of the new technology are now more extensive than ever before.

Key points:
*2014 spec car is most complex race car built by Audi
*V6 TDI mid-engine powers the rear wheels
*hybrid system (ERS-K, standing for Energy Recovery System Kinetic) located at the front axle
*Optimised flywheel energy storage system
*hybrid system with an electric turbocharger in the internal combustion engine (ERS-H, standing for Energy Recovery System Heat.

Tech specs:
Class: LMP1
Engine: V6 TDI
Torque: 800Nm
Capacity: 4000cc
Power: 395kW
Monocoque: Carbon
Drive: rear-wheel-drive quattro
Length: 4650mm
Width:1900mm
Height: 1050mm
Tank capacity: 54.31litres