Mazda’s New Engine Spawns Production Overhaul

When Mazda Motor Corp. created its new 2.5-liter four-cylinder engine for the 2014 Mazda6 sedan, it ended up with more than a new powerplant.

The process also spawned a far more efficient system to produce the engines and a lighter vehicle to put them in.

The new 184-hp SkyActiv engine is an upsized version of the 2.0-liter, 155-hp four-banger that Mazda debuted last year in the CX-5 small crossover. But instead of simply increasing the bore of the smaller engine, Mazda took the unusual step of also increasing the stroke and widening the bore spacing.

The resulting design preserves the efficient gas-flow characteristics of the smaller engine, according to the company. The new unit also is more compact than the V-6 engine used in the previous-generation Mazda6. The difference allowed substantial changes in body structure that contributed to an 89-lb reduction in vehicle curb weight, according to the company.

But changing bore centers for the new powerplant also prompted Mazda to overhaul machining operations at its engine plant in Hiroshima. The factory formerly used a transfer line and 45 machining stations to produce eight engine sizes.

The new system substitutes four flexible NC machining systems capable of handling all five engines in the company's new powerplant lineup: the two I-4 engines, an I-4 diesel and a V-6. Mazda says the new process reduces total machining time per engine from 6 hours to 1.3 hours.

Mazda notes that its new 2.5-liter engine borrows the long-stroke (100 mm) and unusually high 13:1 compression ratio of the 2.0-liter design. The architecture improves efficiency and results in an expansion ratio comparable to some diesels. Yet the powerplant is built to run on regular-grade gasoline, thanks to a dome piston design with "volcano"-like pocket on top that controls pre-ignition.

The new engine also benefits from a lengthy tuned exhaust manifold that improves scavenging. A richer air-fuel mixture helps accelerate catalyst warm up.