Screenshot: Engineering Explained

Automakers are obsessed with turbocharging everything at the moment, being that consumers are demanding ever more power and low-end torque feel from their cars, while attempting to meet fuel economy expectations at the same time. That low-end boost is provided a number of ways, but effectively manufacturers desire the turbocharger boost to help provide additional power from just-off-idle RPM. Mazda has proven particularly adept at the task with their advanced SkyActiv engine family. Engineering Explained is here to help us all understand how they’ve done it.

Mazda has pushed the turbocharger as close to the exhaust valve as they possibly can, though that alone isn’t unique. The turbocharger has effectively become a variable geometry by virtue of that interesting valved manifold it bolts to. By closing off much of the manifold’s cross section at low RPM, the exhaust is bottlenecked through a smaller opening, which increases the velocity of the exhaust gasses as they hit the turbine, spooling it much quicker than it would otherwise. By the time the RPMs get high enough to open that valve, the turbo is already spinning quite well.

Further, by building the exhaust manifold as a four-into-three-into-one, the high-pressure exhaust gasses are paired with the cycle of a paired cylinder’s low-pressure cycle, promoting scavenging. This also helps provide a smooth and continuous flow of exhaust gasses to keep the turbine spooled.

As mentioned in the comments of this video, this 2.5-liter engine from the CX-9 would be a great one to drop into a brand new Mazda3 to create a hell of a hot hatch. And to make that even better, it’d probably get pretty decent fuel economy to go with its power.