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How Mazda got Skyactiv-X to work is incredible

"Take everything you know about engines and turn it around," Mazda North America Vehicle Development Engineer Dave Coleman says, patiently and with a look of benevolent pity, as he's quizzed about the particulars of the company's new engine. The Skyactiv-X engine is enigmatic — and deceptively simple in operation. And the bottom line for American consumers is that they'll be able to buy a car (or crossover; we don't know yet what vehicle will first get it) by late 2019 that provides diesel-like fuel economy but runs on regular old gasoline. In between diesel and spark ignition, but it's neither To truly understand it, you have to dive into the contradictions. Take that regular old gasoline: Contrary to common sense, the lower the octane, the better it works. In the lab, the Skyactiv-X engine loves 80 octane. The lowest Americans get is 87, so the engine is tuned for that octane. Go higher and you lose some low-end torque. Coleman was right. It's hard to wrap your head around an engine that thrives just at the point when most gas engines would aggressively self-destruct. It uses a supercharger to pump additional air — but not additional fuel. It uses spark plugs to start a combustion cycle that normally doesn't need a spark. And, quixotically, it's not displacing Mazda's own American-market diesel engine, currently languishing in a seemingly endless hell of regulatory approval. More bizarre: Mazda is a tiny automaker facing real existential headwinds, and gasoline compression ignition is a massive challenge. GM and Hyundai announced compression ignition, or HCCI, projects (full name, homogeneous charge compression ignition) to great fanfare, but they never amounted to a production hill of beans, crippled by reliability issues or horrible vibrations. Worse, they only worked at an unusably narrow range — low RPMs and low loads. HCCI research improved direct-injection gas and diesel engine technologies for these companies, but HCCI itself remains untamed. The benefits of lean combustion Why even try to tame HCCI? The answer is much better fuel economy and lower emissions. Less burned carbon-based fuel, less carbon dioxide released. That's simple. But there are some thermodynamic reasons for the lean combustion you can achieve with compression ignition that are worth explaining. The ideal amount of fuel for a conventional engine to burn is about a 14:1 air-to-fuel ratio. That lets every molecule burn nicely, in theory.

Petrolicious lets a 1971 Mazda RX-2 howl

Rotary engines scream to the heavens in the best way possible. To hear a wonderful example of the Wankel's battle cry, turn up your speakers and watch Petrolicious highlight an immaculately clean 1971 Mazda RX-2 in Australia. Owner Jason Humble took three years to build his RX-2 from a bare shell, and he started competing with it in vintage racing in 2005. The little coupe's class pits it on track against Mustangs and Camaros, but Humble claims that he's regularly near the top of the pack thanks to the Mazda's communicative chassis. We don't get to see the RX-2 mixing things up on track in the Petrolicious video, but Humble does treat us to a drive through the Australian countryside. He's happy to let the coupe's rotary rev, and the little engine is capable of making a wonderful noise. It's great to see Petrolicious continue to give the spotlight to these sometimes overlooked classic Japanese sports cars.

8 cars we're most looking forward to driving in 2015

Now that 2014 is officially in the books, it's time to look ahead. And following our list of the cars we liked best last year, we're now setting our sights at the hot new metal that's coming our way in 2015. Some of these, we've already seen. And some are still set to debut during the 2015 auto show season. But these are the machines that keep us going – the things on the horizon that we're particularly stoked to drive, and drive hard. Jeep Renegade Not the Chevrolet Corvette Z06. Not the Ford Mustang GT350. Not the new John Cooper Works Mini. Nope, I'm looking forward to the adorable, trail-rated Jeep Renegade. And that's because I really, really, really like our long-term Jeep Cherokee Trailhawk. I do not, however, care too much for the Cherokee's looks, and I really don't like its $38,059 price tag. The Renegade Trailhawk, meanwhile, promises much of the same rough-and-tumble character as its big brother, but at what we expect will be a more reasonable price (I'm personally wagering on the baby Jeep's off-road model starting at no more than $23,000). With a 2.4-liter four-cylinder and a nine-speed automatic, it should also be a bit easier to fill than the V6-powered Cherokee. Also, I can't help but love the way the Renegade looks. It's like someone took a Wrangler, squished it by 50 percent and then handed it off to George Clinton for a healthy dose of funk. The interior, with its bright, expressive trims and color schemes should also be a really nice place to spend some time. I'll be attending the Renegade's launch later this month, so I'll have a much shorter wait than my colleagues. Here's hoping the baby Jeep lives up to my expectations. – Brandon Turkus Associate Editor Mazda MX-5 Miata Here's an uncomfortable truth: I'd rather spend a day driving a properly sorted Mazda MX-5 Miata of any generation on a winding road than I would nearly any other vehicle, regardless of power, price or prestige. It's not just that I prize top-down driving and enjoy the Miata's small size because it gives me more road to play with. I just find there's more motoring joy to be had with high-fidelity handling and an uncorrupted car-to-driver communication loop than I do with face-distorting power or grip – let alone valet-stand gravitas. But perhaps most of all, I love Miatas because they can deliver that level of feedback and driver reward at modest speeds that won't put the locals on edge or endanger lives – you can use more of the car more of the time.