March 2, 2011 Vol. 7, No. 5

Well, well, well… Navistar has just thrown us an interesting bone with last week’s announcement that it’s now involved in the development of an all-new way to power trucks, the ‘OPOC’ engine.

My first conclusion? It’s a great time to be a gearhead truck writer.

That acronym stands for the Opposed-Piston/Opposed-Cylinder engine that’s the brainchild of Prof. Peter Hofbauer, chairman and chief technical officer at EcoMotors International, based in Troy, MI. Navistar has signed a development agreement with that small outfit to help bring its OPOC engine to market.

But here’s another twist: it’s not an exclusive agreement. Don Runkle, CEO at EcoMotors and a General Motors veteran, says the company will announce a similar development agreement with another vehicle and equipment builder later this month. So I’ll hazard a wild guess and suggest that yellow OPOC motors might well exist in years to come.

The first OPOC product targeted for commercial applications is a turbocharged diesel version, but it can actually run on pretty much any fuel except charcoal briquettes by the sound of it. Including gasoline, natural gas, ethanol, even hydrogen.

Could this be the game-changer it’s made out to be? Mighty promising at the very least. Promising enough to have Bill Gates of Microsoft fame as one of two key investors, the other being Khosla Ventures’ Vinod Khosla, EcoMotors’ primary backer.

So what’s this wonder engine all about?

Well, let’s look first at what it’s claimed to offer. Like two to three times the power density of conventional engines with 50% fewer parts and at least 15% better fuel efficiency — rising as power rises to as high as 55%! — with attendant gains in emission levels. Its mechanical simplicity means it should cost 20% less to manufacture, I’m told. And its small stature would mean significant packaging gains and thus truck designs that could better optimize aerodynamic efficiency.

And how about this? An existing prototype pictured here, model EM100, produces 325 hp and 664 lb ft of torque, yet weighs only 296 lb. That’s an astounding power-to-weight ratio of 1.1 horsepower per pound. Yet I believe it displaces just 2.5 litres. In fact, the OPOC equivalent to the 15-litre diesel of today might only be 7 litres, as I understand things.

OK, THE TECHNICAL BITS. Start by thinking about the flat, boxer engines in old Volkswagen Beetles, present-day Subarus, and, if you’re old enough, the Corvairs of the 1960s. The OPOC isn’t just another boxer, however. Hofbauer calls it a cross between the little VW motor and various Junkers aircraft engines that propelled an awful lot of German planes starting in 1929. In a two-stroke design, the Jumo 104 variant had six cylinders and twelve pistons in an opposed-piston configuration with two crankshafts, one at the bottom of the cylinder block and the other at the top, geared together. The pistons moved towards each other during the operating cycle and essentially formed two cylinder heads as they met. The OPOC is a variation on that theme.