Mazda is back in the TUDOR United SportsCar Series with a race car powered by a diesel engine.

At this weekend’s Rolex 24 at Daytona, Mazda’s two SKYACTIV Prototype cars will have the only diesel powerplants in the season-opening TUDOR United SportsCar Series race.

The inline four-cylinder 2.2-liter Mazda engine continues into 2015 with its very particular compound turbochargers and a host of stock-based components, stated Mazda, with work over the winter having led to improvements, helping set lap times at the recent Daytona International Speedway test session that were six seconds quicker than last year’s best. The top speeds have also risen by 20 mph.

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“Last year was the start of a very aggressive development program for Mazda,” said John Doonan, Mazda’s director of motorsports in North America. “Now, in the second year, that development is beginning to pay off. The improvements we have seen are a product of very smart people working very hard to enhance every aspect of the race car. It was great to see that effort show up in the lap times and top speeds, and in the smiles from the drivers and the team.”

Why the big improvements? Mazda said as with most gains in auto racing, it has been a constant and intense process where each small gain leads to other incremental benefits. The multiple changes combine to produce faster and better-driving cars.

“The engine improvement has been good,” said Sylvain Tremblay, driver and owner of SpeedSource, the Mazda factory team. “We improved the engine and the cooling system, and we also focused on aerodynamic gains, weight-saving and more. Mazda’s SKYACTIV philosophy is to make each piece of the car lighter, stronger and provide better performance, and I think we’ve done that. We have a dedicated, in-house engineer who constantly runs simulations for each track, and that has really paid off. The car is faster, but it also handles better and is much more consistent. All of our drivers can go quicker and do it for a longer length of time. We all have a lot more confidence in the car and the engine going into the race this weekend.”

Mazda has 23 class victories in the Rolex 24 since 1975.

For 2015, the 2.2-liter engine produces approximately 475 horsepower and the compound turbochargers can spin at an amazing 180,000 revolutions per minute!