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.

The engine uses 0W20 oil, which looks frighteningly like colored water

To enable running on regular gas, the U.S. version will have a compression ratio of 13:1, which means fuel economy and torque will diminish by about 3 to 5 percent, according to Mazda.

The downside to lowering the compression ratio of a diesel is that, during warm-up, the engine temperature can be too low to support proper combustion, and misfires result. To get around this, Mazda added a two-stage variable valve-lift system on the exhaust side in order to be able to create additional valve overlap. This causes the hot exhaust gases to be drawn back into the next cylinder to warm it up.