A three-cylinder future?

They first came to Canada over 20 years ago. Suzuki built them and then they carried the Suzuki, Chevrolet and Geo brands. The Geo Metro, Chevrolet Sprint and Suzuki Forza were unique for their engine configuration: in-line three-cylinder. Three-cylinder engines had been seen on Canadian roads before; Saab and DKW (one of the “rings” seen today in Audi’s logo) had two-stroke units, but as mainstream cars, the one-liter two-stroke threes were, I thought at the time, a joke. With the two-up-one-down crankshaft arrangement, it seemed clear that there was no way to balance a three, and early examples certainly weren’t the smoothest running engines, nor the most powerful.

When the threes disappeared, that prejudice seemed justified. Now however, they’re back in a big way with Ford proposing to make in-line threes the company’s standard entry-level engine. It’s a good thing. Why? Technology has improved significantly since the 80s and balance shafts can be economically built into cheaper engines today; but there’s more to balance these days. Common rail injection promises to give engineers another tool to smooth power delivery and Ford is using an innovative unbalanced flywheel as well. Engine mounts that react with variable compliance, maybe “smart,” can also play a part.

Why three-cylinders? For small displacement engines, they’re simpler, cheaper to build and have less internal friction overall compared to four-cylinder engines of the same size. They’re also shorter and can share parts with similar V-6 designs. It makes a lot of sense, but who wants a 60 horsepower car? Even with fuel prices north of $1.30 a litre, slow cars have little appeal and three-cylinders have little room for growth through bore and stroke. Suzuki addressed this with turbo-charging and Ford is following suit today. This is the future of automotive piston engines, with small displacement blocks boosted by turbos and superchargers for larger, heavier vehicles. With the ECU controlling boost, it should be possible to build a single engine that powers everything from mini-cars to mid-size sedans with very high fuel efficiency.

Why do we care? Because there are implications for the service industry. Engine mounts will be more important than ever and may become a wear item in some applications. Turbos will likely be small and very fast spinning and lubrication issues may rear their heads if consumers neglect oil changes or use cheap, off-brand oil. “Coked” turbo bearings won’t be a pretty sight. Boost pressures will be higher, making intake plumbing and gaskets more critical than ever. Higher boost pressures will also make the MAP sensor extremely important. I expect that a failed MAP will not just set the MIL, it will trigger a limp-home mode in the engine ECU that will severely limit boost pressure. Drivers will really know they have a problem. It will be one less spark plug, coil and injector to service, but the durability of very small, highly stressed three cylinder engines in tough Canadian service remains to be seen. It’s going to be interesting.