GM Uses Diesel Tricks to Make Its Four-Cylinder Truck Engines Tougher

It would be hard to believe coming from anyone other than Kevin Luchansky, assistant chief powertrain engineer at GM. Speaking at the press launch of the new Colorado this week, Luchansky outlined the diesel-derived design elements and test regimen of what he calls "one of the most durable engines GM's ever made. It's really, really good."

Even with Luchansky's confidence, it's important to understand what worries truck owners about this lump. At 2,727 cc, it's second to only Ford's 2.7-liter Ecoboost V6 for the smallest full-size pickup motor, and the third-smallest among midsize trucks. It runs a relatively high compression ratio of 10:1, with boost pressures up to 27 psi. That results in double the cylinder pressures of a comparable naturally aspirated V8, like the 5.3-liter small-block this effectively replaces in the larger Silverado.

That could mean knocking issues out the wazoo, especially seeing as the 2.7L is designed to run on just 87-octane gas. But Luchansky was adamant that it will hold up to whatever you throw at it because he designed it using diesel engine tricks that help it hold up extraordinarily well in torture testing.

While the 2.7L is nominally an all-aluminum engine (keeping long-block weight down to 331 pounds), it actually has iron cylinder sleeves cast into the block during manufacturing. It's a more modern material though, so Luchansky says it won't wear in the way many older cast-iron blocks do.

Its pistons are an aluminum alloy too, with machined heads to optimize material properties, and cast-iron ring carriers to hold onto the rings at high cylinder pressures. In lieu of typical molybdenum-coated iron rings, the 2.7L uses diesel-grade steel rings with PVD coatings, reducing friction and slowing wear.

The four-pot's extreme torque output of up to 430 pound-feet means it needs serious bearings too. That's why Luchansky and GM's engine team chose not to use common bi-metal rod bearings—with aluminum alloy over a steel backing—but tri-metal with an added layer of copper alloy to remove more heat.

The result is an engine that can withstand being abused for literally weeks on end—which is how Luchansky says GM tested the 2.7L. Those are his words: GM dyno-tested it at wide-open throttle "for weeks" straight, making prototypes' pistons glow and wrist pins discolor purple from the heat. GM's also torn down engines bought back from customers who drove without oil, all to find failure points whose fixing has already significantly lengthened the engine's service life. In fact, the upgrades have meant that even extreme cases might not even wipe off the manufacturing sticker from the inside of the bearing.

"We're now running 25 percent longer than we did before," Luchansky said of the engine's design improvements. "We have over the years made things stronger and better. It's one of the reasons we can crank the torque up as much as we can."

Luchansky and the team know however that he can't force this engine down truck buyers' throats, and that it has to establish a reputation on its own. "It just has to prove itself, and it is proving itself," he said, adding that GM has already sold over 300,000 trucks with these engines, receiving strongly positive feedback.

"The people that own 'em, they love 'em," Luchansky said. "If you talk to the dealers, they're like, the 2.7L is rarely in for service."

But again, the real test will be out in the world, where people will miss oil changes and overload trailers. GM's work will have to speak for itself, whether that means the 2.7L worms its way into people's hearts or sours them on the engine entirely. By the way Luchansky talks about GM's baby, it sounds like we should expect only the best.

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