(Quietly) Racing the Mazda 6 Diesel
The diesel-powered Mazda 6 is Mazda's stealth vehicle. You can't hear it on the racetrack, and you can't see it in North American showrooms. At least, not yet.
Although the Skyactiv-D version of Mazda's four-door sedan is sold just about everywhere else in the world, it isn't yet offered in the United States. The engine can't meet California's demanding emissions standards while maintaining the level of performance that the company's brand image demands, so Mazda is waiting until further engineering developments enable the car's introduction.
But Mazda hasn't jumped off the diesel bandwagon. "We're still committed to bringing diesel to North America," says Robert Davis, senior vice president, Mazda US Operations. "It separates us from the other Japanese manufacturers and it allows us to compete with Germany near-luxury cars."
Imagine the stealth-fighter edition of the Mazda 6
Not so long ago at Buttonwillow Raceway Park in Southern California, I got a chance to sample the future by racing an example of the forthcoming Mazda 6 Skyactiv-D. It looked spectacular, accelerated like a turbine, made amazing fuel mileage and was so quiet that all I heard throughout the race was voices on my radio intercom with the pits and the snarl of the other, conventionally powered race cars around me.
Spiritually, the Mazda 6 diesel is the outgrowth of a program that Mazda began with SpeedSource Race Engineering, its longtime motorsports partner. Last year, a jointly developed Skyactiv-D motor powered a Mazda 6 to a championship in the GX class in IMSA's Grand-Am (albeit, not a class overrun with competitors).
This year, the SpeedSource team has moved up to the top-tier prototype class in IMSA's new United SportsCar Championship. The Mazda-powered Lola prototypes have been way down on power and speed in the opening races at Daytona, Sebring and Long Beach, and it's going to be a long season for them.
But just to show that Mazda remains committed to diesel on the street even as it awaits the readiness of the Mazda 6 Skyactive-D, Robert Davis decided last fall to build a trio of production-based diesel-powered Mazda 6s for the 25 Hours of Thunderhill, an amateur-level racing event sanctioned by the National Auto Sport Association (NASA).
It's mostly stock, so it should be easy to build, right?
Just nine weeks before the race last December, three Russian-spec Mazda 6 diesels were imported to the U.S. Although the protective rollover cages were installed by AWR Racing in Vista, California, virtually everything else to prepare the cars for competition was done by a dozen or so Mazda volunteers working nights and weekends at Mazda Research & Development in Irvine, California. "It was a LOT of work," says Nathan Edwards, a manager of field technical operations for Mazda who also drove one of the cars in the 25 Hour.
Virtually nothing, however, was done to the Mazda diesel engine in each car. It's straight off the assembly line, a turbocharged 2.2-liter inline-4 that makes 165 horsepower and an impressive 300 ft-lb of torque at a measly 2400 rpm. The only major change to the drivetrain was the replacement of the stock open differential with a custom-made limited-slip item from Wavetrac.
On the suspension front, Koni dampers, Hypercoil springs and a custom-made rear anti-roll bar from ProParts USA were added. Under the fenders, 245/40R-17 BFGoodrich g-Force R1 tires went on 17-inch Enkei wheels. Big brake rotors and four-piston STR-40 calipers from StopTech were added up front, while stock brakes with Cobalt Friction pads were used in the rear. As a result, Mazda public relations director (and diesel racer) Jeremy Barnes says, "One car did the whole 25 Hour without changing pads."
At Thunderhill, the Mazda 6 diesels finished 3rd, 4th and 6th in class despite competing against much more radically modified cars. The diesel engines were so fuel efficient that a full tank enabled nearly four hours of driving under racing conditions.
It might be a diesel, but it makes you look like a hero
As I walked up the Mazda 6 Skyactiv-D at Buttonwillow, it looked great. With the strip of LEDs in the light bar across the hood, the big wheels and tires, and a dramatic graphics package created by Mazda design manager Ken Saward (yet another Mazda employee who is a racer), this car was positively bad-ass.
Thanks to all the Sparco safety gear inside the cockpit, the 6 also felt like a proper race car to me. But when I punched the starter button, I had an unnerving electric-car moment. That is, I wasn't sure if the car was running or not. With radio earpieces in and a helmet on, the engine became effectively silent. This was unnerving on the track, where other cars seemed unnaturally loud. Sometimes I wasn't even sure where the noise was coming from, and I found myself frantically checking my mirrors for traffic.
And there was a lot of checking of mirrors. Thanks to a modest power-to-weight ratio, this 3200-pound Mazda 6 and its two identical partners were among the slowest cars in the race. The car's handling, though, was surprisingly benign. Because it's a front-wheel-drive car with scads of torque, I was expecting a ton of understeer. In fact, the rear anti-roll bar had been made stiff enough to produce plenty of lift-throttle oversteer to help the car rotate its nose toward the apex while entering corners.
Just like driving to the store
In my case, the Mazda 6 diesel rotated a little too well on a couple of occasions, but this was a running-out-of-talent issue rather than a flaw in the handling dynamics. Otherwise, the Mazda 6 diesel rarely exhibited any of the deficiencies associated with front-wheel drive -- torque-steer, aggravating push, etc. -- and it was a pleasure to drive on the track.
The brakes were another surprise. Despite the car's mass, the car stopped so well that I could drive deeper into the brake zones than lighter cars. The diesel was also stout coming off corners, where the luxury of 300 lb-ft of torque allowed me to out-drag more powerful cars, at least until their engines were fully wound up. (With a compression ratio of 14:1 -- low by diesel standards -- the Skyactiv-D revved to 5200 rpm, but it ran out of steam long before then.)
Just as Barnes had told me beforehand, I found myself changing my style when it came time to use the gear lever. In general, the corners could be easily taken a full ratio taller than you'd expect. The Mazda people engineered a system of lights to help you keep track of the engine rpm and the recommended shift points, and I found myself shifting very early and just riding the steeply increasing wave of torque as the engine wound up. No red mist was required.
The success or failure of diesels in racing depends as much on the whims of the rules-makers as it does on the ingenuity of the engineers, much as Mazda has discovered with its IMSA prototype. But if my experience at Buttonwillow with the Mazda 6 Skyactiv-D is any guide, it is possible to drive a street-legal diesel in a way that is both fast and rewarding. Just stop trying so hard, get used to the peace and quiet, and then give a polite little wave when you sail silently past the competition.