Ars Technica takes an in-depth look at some of the tech side of the hybrid racing circuit, in particular the World Endurance Championship . From the article: Hybrid systems are allowed to deploy between 2MJ and 8MJ of energy during a single lap of Le Mans, augmenting the power from an internal combustion engine. Energy can be recovered from up to two motor/generator units (MGUs); usually this means recapturing kinetic energy from the front and rear wheels under braking. To balance things out, cars that recover and deploy 8MJ carry less fuel, and the flow rate at which they can feed it to the engine decreases. Audi's R18, with its mix of turbo diesel and flywheel hybrid technology, was king of the hill for several years, but the hybrid systems were much less powerful. Last year, Toyota's gasoline V8 and supercapacitor-powered TS040 was the car to beat. But 2015 is the year of the Porsche 919 Hybrid. Porsche chose lithium-ion batteries to hybridize the 919's turbocharged gasoline V4, and this year is able to capture and deploy the full 8MJ (Toyota is in the 6MJ class and Audi 4MJ). The article spends more space on Audi's approach than the others, but offers a cool glimpse at all three of these companies' niches within the field, as represented at the Texas' Lone Star Le Mans.