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From the race to the road: How Mazda puts its Skyactiv diesel tech to the test on the track

They say racing improves the breed, but as but both race cars and road cars have become more complicated, that line has had less meaning for carmakers.

Nowhere is this more apparent than in Watkins Glen, New York. Where lightly-modified sports cars once raced through village streets, teams roll up in air-conditioned mobile garages, brandishing seemingly limitless amounts of computing power and carbon fiber in the pursuit of speed.

However, Mazda is trying to close the gap. Working with longtime partner SpeedSource, the Japanese carmaker has been racing the “Skyactiv-D” diesel engine it plans to launch in the U.S., first in a six touring car in the defunct Gran Am series, and now in a full-blown LMP2 prototype in the new Tudor United SportsCar Championship.

We shadowed the Mazda team during the 2014 Sahlen’s Six Hours of The Glen to see what it takes to build a competitive racecar around an economy-car engine, and to find out how all of that effort could translate to the cars people who don’t wear fire suits to work can buy.

Small engine, big punch

With its carbon-fiber monocoque, pushrod suspension, and array of spoilers and dive planes, the Mazda Skyactiv diesel prototype looks pretty exotic. Yet beneath the swoopy bodywork is the same puny 2.2-liter turbocharged four-cylinder diesel engine that’s already powering sedans and crossovers in Europe.

Mazda is quick to note that, although it powers a car in the top Prototype class, the engine is 51 percent stock. Certain internal components were beefed up, and other modifications were made to allow the car’s suspension to be mounted directly to it. To keep weight down, the engine is actually part of the chassis.

A half-stock engine might do in a racecar, stock power certainly won’t. So while the stock Skyactiv diesel has a single turbocharger, this one has two. They work in sequence, with a low-pressure turbo getting things started, and high-pressure one keeping the boost going.

The result is 450 horsepower and just under 600 pound-feet of torque, compared to 173 hp and 310 lb-ft of torque in its most potent stock form. That power is sent to the rear wheels through a six-speed sequential gearbox with electro-pneumatic paddle shifters.

That all sounds very intriguing on paper, but what’s the biggest difference from behind the wheel?

“The torque”, exclaimed Sylvain Tremblay, SpeedSource owner and one of the drivers of the number 70 car.  In early states of tune, the turbos’ boost would come on so violently that it would instantly break loose the rear tires.

Managing the nonlinearity of the diesel engine has been one of greatest challenges for both drivers and engineers.

Tristan Nunez, part of the driver contingent for the number 07 prototype, said the car also suffers from the “turbo lag” that’s only recently been banished from gasoline production engines. The turbos don’t kick in until about 3,000 rpm, fairly close to the engine’s 4,700-rpm power peak, so there’s only a narrow window to exploit.

The diesel lacks the on-demand power delivery of a naturally-aspirated gasoline engine, Nunez said, but “when the power comes in … it kicks you.”

Constant improvement

Meanwhile, the more complex powertrain makes extra work for the engineers who sit behind screens in the pit, watching trend lines on telemetry graphs for hours on end as the cars roar by.

Added parts like the turbochargers and diesel-specific fuel-injection rail all have to be watched. The 4G-based telemetry system can monitor up to 200 parameters, but engineers generally focus on around 30, trying to analyze the car’s health in real time.

It’s enough data to make the NSA jealous, and on race day it’s all used to help the driver go faster without blowing up the car. While engineers watch for potential problems, the off-duty drivers monitor things like steering angle and rpm to find ways to improve pace.

Once the race is over and the data is downloaded, data trends are analyzed to help improve the car itself. The team hopes to consistently match the power output of the other Prototype-class cars, while consuming half the fuel.

Fuel efficiency is obviously prized by both race-car and road-car developers, but the latter also have to deal with emissions regulations. That’s one reason why most of today’s race cars have so little in common with street cars.

So while some efficiency and reliability improvements may cross over from track to road (and vice versa), there isn’t wholesale collaboration between the race team and the factory.

Going green

It would be great if future cars could be sporty and use less fuel, but what about the fuel itself?

The Mazda racer uses a “synthetic diesel” made from fats and oils left over from meat processing. So it’s renewable and makes use of the meatpacking industry’s waste.

It’s also good for performance. John Doonan, director of motorsports for Mazda in North America, noted that the team saw increased power output after switching over from pump diesel. That’s down to the meat fuel’s higher cetane rating (analogous to the octane rating of gasoline) of 70, compared to 40 or 50 for conventional diesel.

Best of all, no modifications were required to run the synthetic diesel. That means it could be a viable alternative fuel for production vehicles, but someone will have to take an interest in selling the stuff at gas stations before that assumption can be fully tested.

On the track

It certainly didn’t seem to slow the Mazda prototypes down when the green flag dropped at Watkins Glen last weekend.

The pair of Mazda prototypes made their way around the circuit in eerily silent fashion, something enthusiasts might have to get used to if high-performance diesel cars ever become mainstream.

Unfortunately for the team, things didn’t stay so serene for long. Less than an hour into the six-hour race, the number 70 car retired with an oil leak. The cylinder head had bowed out, breaking the seal with the block and demonstrating the limitations of that particular part.

The remaining number 07 car was slowed down by a suspension problem early in the race and finished mid-pack. Sitting in the paddock waiting to be packed up, the dirt-strewn machine showed that using racing as a laboratory isn’t always glamorous.

From pit lane to showroom

Normally, car geeks have to cross their fingers and wait to see if the latest racing tech will make it to cars they can actually buy, but with this racing Mazda, things were supposed to play out differently.

The debut of the Skyactiv Diesel prototype was supposed to coincide with the U.S. launch of the engine in Mazda road cars, but that’s been pushed back because the company feels the stock engine doesn’t produce enough power in its current state.

While factory engineers try to give the road-going diesel a little more moxie, the race engine soldiers on, pushing the limits of the production parts, and occasionally breaking them.

Beyond proving the durability of a specific engine, the Mazda prototype program shows one possibility for fun-yet-efficient future performance cars, and a renewable fuel to power them.

Stephen Edelstein
Stephen is a freelance automotive journalist covering all things cars. He likes anything with four wheels, from classic cars…
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