When three Mazda 6 sedans roll onto the starting grid for the Rolex 24 endurance race on Saturday, they'll be packing a technology the company says has never before competed at the Daytona International Speedway: diesel engines.
Mazda is no stranger to the annual 24-hour event, the traditional kickoff for the sports-car racing season in the United States, having won its class there 23 times. But its debut with diesel-powered sedans will come as a surprise to many of the automaker's fans, who are used to seeing RX-7 and RX-8 sports cars, with their earsplitting rotary engines, take the checkered flag.
The new racing program, supported by Mazda engineers in Japan and North America, aims to publicize a 2.2-liter turbodiesel engine that is one element of the company's Skyactiv strategy to improve efficiency. The plan lifts a page out of the playbook that Audi has used so successfully at the 24 Hours of Le Mans: using racing to demonstrate the engine's mettle and to increase awareness of diesel's benefits.
"We think diesel, with its great low-end torque, durability, performance and fuel economy, fits the Mazda brand's enthusiast reputation -- and we hope the racing program will demonstrate that," said Jim O'Sullivan, chief executive of Mazda North America.
Gasoline-powered versions of the 2013 Mazda 6 began arriving at United States dealerships this month, and the diesel engine will be available as a 2014 model late this year. Mazda's last diesel vehicle in the United States, the B2200 pickup truck, was offered in 1982-85.
Rather than install the Skyactiv-D diesel in a purpose-built chassis and enter it in a prototype class, Mazda instead decided to use the body of the production sedan. And to showcase the engine's reliability, power and efficiency, the engine would use as many standard parts as possible.
"When our engineers first looked at the new Sky-D they got excited about the level of power we could get from an engine this size," said Sylvain Tremblay, president of SpeedSource Engineering, a Florida company that has been closely affiliated with Mazda's factory racing since the 1990s.
The team found that it could use more than half of the stock engine's parts, by weight, to create the racing version. Uncommon for a high-profile factory racing program, more than 275 parts come directly from Mazda's assembly line, including the cylinder block and heads, valves and water pump -- the latter outperforming every specialized racing pump the team tested.
SpeedSource built the three Daytona racecars and their engines, which will use a clean-burning synthetic diesel fuel to produce more than 400 horsepower, compared with the 173 horsepower of the production Skyactiv-D engine. Prerace testing has shown the diesels will burn 25 to 30 percent less fuel than a comparable gasoline racecar over the same distance. That enables them to carry a fuel tank that is three to four gallons smaller, and thus lighter, than their competitors' fuel loads.
Better yet, like its production cousin the racing Mazda 6 diesel does not use urea injection or particulate filter aftertreatment systems for the exhaust, typically needed on diesel-powered vehicles to meet emission regulations. While such hardware helps eliminate tailpipe emissions on some diesels, it also is heavy, expensive and reduces fuel efficiency. Engineers credit the stock engine's low 14:1 compression ratio, combustion chamber shape and the sophisticated turbocharging setup for its clean combustion, which also benefits the race engine.
Many other parts are either modified stock items for greater performance, like the camshafts, or racing parts that share key elements with the standard part, like the pistons' bowl-shaped dome, which is critical for efficient combustion. A stock crankshaft proved itself durable throughout testing; it was replaced with a stronger aftermarket crankshaft only to increase the time between engine rebuilds to at least 30 hours during the season, Mr. Tremblay said.
"We tried to out-engineer the factory, but we weren't able to do that in many cases on this engine," he said.
The racing Skyactiv-D also features a compounded turbocharging system, which Mr. Tremblay said was a first in motor sports. In this arrangement, one large low-pressure turbocharger draws in and compresses ambient air, feeding it into a smaller high pressure turbo that compresses the air again and pushes it to the intake manifold. Compared with a single turbocharger, the compounded-turbo set-up offers a greater range of operating efficiency, said Mr. Tremblay, though it is more complex and difficult to package in the car.
The addition of Mazda's new diesel to the Daytona grid, and to the 11 Rolex series races that follow in 2013, was cultivated by Grand-Am, the road race sanctioning organization. Late last year Grand-Am announced its new GX class created for cars and powertrain technologies not currently involved in the Rolex series or ill-matched against the much faster GT class cars.
"Grand-Am welcomed us with open arms," Mr. Tremblay said, adding that the GX rules were aimed at encouraging diesels, hybrids and alternative clean fuels other than gasoline.
At Daytona, SpeedSource will campaign the No. 70 car with Mr. Tremblay sharing driving duties in the grueling daylong event. The No. 25 and 00 cars are sponsored by independent teams Freedom Autosport and VisitFlorida.com Racing.
After a test session at Florida in early January, Mr. Tremblay reflected on Mazda's challenge with its latest racecar.
"Before us, the only people who have played with road-racing diesels are Audi and Peugeot, and they were both bespoke prototype programs without a single stock part, so there's little data and technology transfer that applies to what we're doing," he said. "We're basically alone and forging new ground with this program."
"I believe there's a place in motor sports for diesel and hybrids," he said. "And what better proving ground than the Rolex 24 Hours of Daytona?"
This article originally appeared in The New York Times.