How Mazda Reduces Turbo Lag In SkyActiv Engines

HotCars

By Sean Murray

Published May 12, 2018

Mazda's SkyActiv engines have a pretty novel way of reducing turbo lag, and it's all in the design.

via Car Throttle

Ever wondered how Mazda makes such incredibly fuel-efficient but peppy engines? This new video explains everything.

Mazda has managed to maintain a reputation that holds it apart from other Japanese carmakers. Where Toyota is boring and reliable, Mazda is sporty and exciting even in cars that aren’t particularly sporty or even mildly exciting. The reason for that is all in their performance, which always seeks to maintain a balance between efficiency and that ineffable quality that Mazda used to call “Zoom Zoom”.

How do they do it? As Engineering Explained, well, explains, it all has to do with how Mazda has managed to eliminate turbo lag in their SkyActiv engines.

The first feature unique to SkyActiv engines is a valve located in the exhaust manifold that artificially shortens the path the exhaust gas takes to the turbocharger. Just like how placing your thumb over a hose makes water spray out faster, so too does the valve cause the exhaust gasses to strike the turbofans quicker and allow it to spool up faster.

This sort of gives the SkyActiv into a variable geometry exhaust depending on the engine’s load. The valve only activates at below 1620 RPM to improve low-rev performance and is nestled into the manifold at higher revs. If the valves were open at higher revs it’d spool up the turbo so fast it would explode.

The second feature of the SkyActiv engines has to do with what’s known as “scavenging.” This is the process by which remaining exhaust gasses are sucked out of the cylinder by the activation of the next cylinder. To do that, the manifold connects the exhausts from cylinders two and three and fires them in such an order that the firing of one cylinder is always adjacent to the exhaust of another cylinder.

The firing order is 1, 3, 4, 2. This means that when cylinder 1 is firing it’s also sucking out the exhaust from cylinder 2, while when 3 is firing it sucks out the exhaust from cylinder 4.

Check out Engineering Explained’s video for a bit more in-depth explanation as well as fantastic sharpie diagrams.

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