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Episode four of the Corvette Racing video series is out, with a focus on the Michelin Green X Challenge and how it's helping to make the C6.R both faster and more efficient. We already knew that the Corvette C6.R has been running on cellulosic E85 for the past two years, but that's just the beginning of the improvements to these race cars.

The engineers and technicians that create and maintain the racers have been working for a decade to make them better. When the original GT1 class C5.R started racing ten years ago, it would get about 10 laps per tankful at Le Mans. Today the cars get 15 laps per tank, meaning they spend a lot less time sitting idle in the pits and more time out running for position.

Reducing friction and parasitic losses throughout the car has helped tremendously. The team has worked with its air conditioning supplier to reduce the compressor power draw from five horsepower to just 1.8 hp. Similarly, going from traditional steel wheel bearings to ceramic bearings has added three mph of straightaway speed and improved durability. The next big change that could eventually make its way to road cars is zero viscosity engine oil to cut internal engine friction. Check out the video after the jump.