Around the world, automakers are grappling with the changes necessary to meet escalating fuel-economy regulations. To this end, Mazda is launching a new family of four-cylinder engines—fours power the vast majority of Mazda’s cars—called Sky-G (gasoline) and Sky-D (diesel). We drove both in prototypes of the next-gen Mazda 6 and, thankfully, either engine can be paired with the latest version of Mazda’s snick-snick six-speed manual.

We got the deep dive on the 2.0-liter version of the Sky-G, which will launch next year in the U.S., likely as part of a midcycle face lift of the Mazda 6. (A completely new 6 is a few years out yet and will be about 140 pounds lighter than the current car, thanks to meticulous optimization of material thicknesses and mounting points.) In the future, there also will be variations in the 1.3- to 2.5-liter realm, and Mazda has already signed a deal to license Toyota’s hybrid technology for a future Sky-based hybrid. Starting from the ground up, Mazda has impressively leapfrogged its previous gas engine, to the tune of estimated EPA fuel-economy ratings in a Sky-equipped Mazda 3 of 30 mpg city and 39 to 40 highway. That’s nearly on par with VW’s Golf and Jetta diesels as well as best-in-class cars one segment smaller, such as the Ford Fiesta and Chevrolet Cruze. Here’s how they did it.

The Big Squeeze

Increasing the compression ratio—in this case, to a staggering 14:1 from 11:1 in the current 2.0-liter (the U.S. version is 10:1)—is a classic way to squeeze more work out of the piston’s power stroke. But it creates problems, too, because compressing the air/fuel mixture this much causes excess heat build-up in the cylinder, which leads to premature auto-ignition, or knock. To keep the temperatures down, Mazda employs a seriously lengthy 4-2-1 exhaust header, designed so that the hot exhaust gases don’t get pulled back into the next cylinder’s intake stroke. As it stands today, it doesn’t appear that the Sky could fit in a longitudinal application such as the Miata—the huge header likely would poke through a front fender.