Pinnacle Looks Beyond Detroit as the Market for Its Opposed-Piston Engine

When Ecomotors International set out to change the way car and truck engines are built, it set up shop in Livonia, MI, a suburb of Detroit, in hopes of eventually licensing its technology to the big U.S. automakers. It was a calculated risk. As radical as Ecomotors’ opposed-piston engine design may be, at least the company’s founder, Peter Hofbauer, has unquestionable auto-industry credentials—he’s the guy who helped Volkswagen build its first mass-production diesel engine.

Pinnacle Engines isn’t even bothering with Detroit. The San Carlos, CA, startup, which recently won the backing of the world’s largest venture capital firm, is also developing an opposed-piston engine, one that promises to marry the fuel efficiency of diesel technology with the lower cost structure of gasoline-burning engines. But Pinnacle’s founder, James Montague “Monty” Cleeves, is a veteran of the semiconductor industry; for him, designing engines and tinkering with cars was always an avocation, not a profession. He’s pretty convinced that Detroit will never listen to his ideas—so Pinnacle is looking farther east for its first commercialization opportunities. Much farther east. To India, in fact.

“This ought to be music to Detroit’s ears, but to them I’m just some whacko in California,” says Cleeves. “This is Silicon Valley, and what does Silicon Valley know about making engines? Folks in Asia have almost zero ‘not-invented-here’ issues, whereas it’s pretty prevalent all over the U.S.”

Pinnacle won its first funding in 2007 and has been testing prototype engines based on its patented “Cleeves Cycle” since the spring of 2009. This year, Pinnacle struck a joint development agreement with an Indian scooter manufacturer—it can’t yet reveal which one—that could see the technology move to the test track by next year and into commercial production by 2013.

But to buy a Pinnacle-powered scooter, you’ll have to go to Mumbai or Bangalore. With gas prices here stable at around $3.50 per gallon, “I don’t know what it’s going to take to get somebody in the U.S. excited” about fundamental improvements to the venerable internal combustion engine, Cleeves says. “But most of Asia is sensitive enough about fuel economy that they get it.” For many families in India, a two-wheeler is the main mode of transportation, and a scooter engine that consumes 25 to 50 percent less fuel, as Pinnacle promises, could be a big boon for the household budget.

Cleeves says his engine can also be scaled up for larger vehicles, and can easily be modified to run on diesel, ethanol, or even compressed natural gas, which means it could also turn up in light commercial vehicles or even cars in India or China. But the startup, which has raised $13.5 million from venture giant New Enterprise Associates (NEA) as well as Bessemer Venture Partners and Infield Capital, doesn’t see its engine as a cure for petroleum addiction. Instead, Cleeves describes it as a bridge technology, incrementally improving the efficiency and lowering the emissions of internal combustion engines as a warming world weans itself from carbon-spewing technologies.

“It’s going to take a long while for Detroit to adopt new technologies,” says Pinnacle CEO Ron Hoge, a veteran of diesel engine maker Cummins. “They may surprise us—it may happen faster than we think. But it’s not even important to us on a business level, because the opportunities we are uncovering in Asia are going to be massive and much more accelerated and have a bigger impact on world consumption of petroleum.”

The basic concept of an opposed-piston engine is so simple that it’s remarkable how long automakers have been ignoring it. In a traditional engine, each piston sits in its own cylinder, and combustion occurs inside the cylinder head, where intake and exhaust valves regulate the inflow of air and vaporized fuel and the outflow of exhaust. In an opposed-piston engine, there’s no cylinder head: two pistons move toward and away from one another inside the same cylinder, with combustion occurring in the in-between space at the moment of greatest compression. Without the cylinder heads, the engine is lighter, and the dual-piston action means compression ratios are higher, so it gets more bang for the buck.

The concept of putting two pistons in the same cylinder is pretty old—manufacturers like Junkers and Fairbanks-Morse started using opposed-piston designs to power aircraft and submarines as long ago as the 1930s. But until Pinnacle came along, all opposed-piston engines (including the Ecomotors engine, and a diesel opposed-piston job from Achates Power in San Diego) were two-stroke engines, meaning there’s one powered stroke for each two movements of the piston. Diesels, motorcycle engines, leaf-blower engines, and other two-stroke engines are powerful but dirty. The problem is that the intake and exhaust functions happen simultaneously in the brief moment when the piston is at the bottom of the cylinder, which makes it difficult keep the burnt exhaust and the incoming air-fuel mixture from getting mixed up.

The Cleeves Cycle engine, by contrast, is a spark-ignited four-stroke engine, just like most conventional gasoline engines. The whole thing hinges on a clever sleeve-valve design that Cleeves says first occurred to him back in the 1970s. (While Cleeves always had a day job helping to improve semiconductor manufacturing methods for companies like Fairchild, Candescent, Cypress, Matrix, and Kovio, he says he spent most evenings in his garage at home, “wrenching on classic cars and hot rods.”)

In Cleeves’ arrangement, metal sleeves move independently on the left and right sides of the cylinder, activated by rocker arms on the camshafts. The cycle starts with Stroke 1; as the pistons move apart, the right sleeve slides open to expose the intake port, and fresh air and fuel are sucked into the cylinder. On Stroke 2 the right sleeve closes, the pistons move together, and the fuel-air mixture is compressed. At the very end of this stroke a spark ignites combustion. In Stroke 3, the only powered stroke, the pistons are pushed apart again; at the end of this stroke, the left sleeve opens and exposes the exhaust port. On Stroke 4, the pistons come together again, carried either by momentum from a flywheel or by power from adjoining cylinders. This squeezes the burnt exhaust out, clearing the way for the next cycle. (If you don’t have it all in your mind’s eye quite yet, just stare at this animated illustration on Pinnacle’s website for a few minutes.)

Under the four-stroke opposed-piston design, “There’s very little mixing of fresh charge with spent charge, the intake air temperature is very well controlled, and doesn’t get heated by residuals from the previous cycle,” explains Cleeves. On top of that, the geometry of the combustion chamber means the exploding vapor expands through a larger volume than in a traditional four-stroke engine.  It’s “basic thermodynamics that with bigger expansion ratios you get more efficiency,” Cleeves says. In essence, the Pinnacle engine extracts more work from the same amount of combusting fuel before the exhaust is vented.

And there’s one more advantage to the opposed-piston design. Simply by changing the spacing between the two pistons, Pinnacle can adjust the compression and expansion ratios to accommodate different fuels. Diesel fuel requires a higher compression ratio than gasoline; ethanol higher still.

While he had his sleeve-valve inspiration early on, however, Cleeves says it took him another 30 years to come up with “the other seven or eight systems that have to be pulled together to make an engine that plays.” It’s all in the omnibus patent Cleeves filed in 2006, just before founding Pinnacle.

The company now has 16 employees, including 10 engineers. The core team works from a modest office and garage space in San Carlos, which is sandwiched mid-peninsula between Redwood City and San Mateo, while a few others are based nearly full-time in India. Hoge says Pinnacle’s venture funding will carry it well into 2013, by which time, it’s hoped, the Indian partner will have a product on the market. That, in turn, is envisioned as the stepping stone to larger partnerships and perhaps strategic fundraising opportunities. “I am confident that when we have that happening, there are manufacturers that will be able to look at our designs and take us seriously,” says Hoge.

But right now, all Pinnacle has is a working model, which it’s been testing for months on dynamometers (devices for measuring torque or power) in Berkeley and in its own just-completed test cell in San Carlos. The prototype—complete with colorful plastic knobs and Plexiglas windows so that testers can view the camshafts—is clearly just that.

Given time, elbow grease, and thousands more hours of testing in the lab and on the track, Pinnacle could have something big, as Hoge predicts. But when you talk to people from the big automakers, the skepticism you hear toward new engine architectures is striking—and you begin to understand Cleeves’ decision to detour around Detroit. Even some of the most forward-thinking engineers at these companies doubt that Pinnacle, Ecomotors, or Achates can come up with something better enough that it would be worth retooling engine factories.

“There are 50 opposed piston engine companies out there, and they all haven’t gotten to the point where they’ve figured out what their Achilles’ heel is,” says Byron Shaw, general manager at GM’s Advanced Technology division in Palo Alto. Shaw’s job, as I explained in a September profile, is to interface with the Silicon Valley software community to make sure GM has access to the latest technologies for in-car information and entertainment systems. But Shaw says he’s an engine guy at heart, and that he’s seen it all in his time.

“It’s unlikely that [the engine startups] have discovered something that isn’t known,” he continues. “Let’s say they really improve the ability to run air flow ratios super lean, but then they haven’t solved the NOx problem [nitrogen oxides, a by-product of combustion and the source of smog and acid rain]. There is always a ‘but,’ and most of these companies haven’t gotten to the ‘but’ yet. In India and China they don’t have any idea what the ‘but’ is. They are a pure growth trajectory. But as those markets mature, so will their expectations.”

As if to illustrate Cleeves’ point, Shaw tells a story from his days as a young, just-out-of-college engineer at GM in 1988. “I came up with this change to an internal part of the air conditioning compressor,” he says. It was part of a project to switch over to a new, environmentally safer coolant. “It passed every test. I was rocking and rolling. I was going to change the world. My boss said, ‘Okay, why don’t you get on the plane and go down to the plant and tell them all about it.’ So I go down there and I start to give my spiel. And the plant manager says, ‘Let me give you a tour of the factory.’

“He shows me where the blank aluminum comes in and where it’s machined and processed. And then he takes me down this line of machines. There are 320 steps and each machine does one step and it’s really fast and precise. And at the end of the line this part rolls off. And he says ‘The part you want to change is machined on step number two. And on every machine after step number two, that’s where they grab the part and hold it to do all the subsequent machine steps. So we’d have to retool 320 machines. Is your change that good? How much more are people willing to pay for their cars based on the improved performance from your little part change, versus what it’s going to cost the company?’ That was a really interesting lesson for me.”

In a world where big innovation costs big money, in other words, all the incentives are geared toward encouraging smaller, less costly changes. That’s exactly the problem Hoge says he wanted to help solve when he decided to leave the venture world, where he’d been consulting with NEA and several other firms, and jump back into management to help Cleeves build Pinnacle Engines.

“If you are going to make a real, fundamental difference in the next 20 to 30 years, you have got to deal with fossil fuel demand,” Hoge says. “I see the size of the problem as an engineer and I also see the challenge of incremental thinking—big, structured companies using 50-year-old technologies. Real invention comes from somebody outside with a passion, who’s not mired in the traditional thinking. That’s Monty.”

Of course, internal combustion itself is about as traditional as it comes. The problem is that alternatives like battery-powered electric vehicles don’t match the performance of gas-powered cars, and are still far too expensive for mass adoption. It’s only by rethinking the old spark-ignition engine that vehicle makers will be able to raise fuel economy while at the same time moving away from petroleum-based fuels, Cleeves argues.

“This engine has the capability to ease the transition from fossil fuels to bio-derived fuels,” he says. “The energy density of alcohol is so poor [compared to gasoline] that right now it has to subsidized. The variable compression ratio mechanism allows us to pull some of the efficiency out of alcohol that you wouldn’t get in a traditional engine. So you can have much greater fuel economy as the price point for alcohol goes higher.”

Cleeves and Hoge say Pinnacle’s next goal, after the scooter deal, would be to try the engine in a light commercial vehicle such as an auto rickshaw (known in popular parlance as a tuk-tuk), and then to continue “blocking and tackling,” as Hoge puts it, until the engine is ready to put into an actual car. “We are funded and we have proof points, but it’s not nearly at the point where we’ve got an engine that we can hand to an auto manufacturer,” he says. “The longer we can go independently, the better the deals we could structure. 2012 will be an active year. I’m very confident we will find a lot of interest.” Just not in Detroit.

Wade Roush is a freelance science and technology journalist and the producer and host of the podcast Soonish. Follow @soonishpodcast

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12 responses to “Pinnacle Looks Beyond Detroit as the Market for Its Opposed-Piston Engine”

  1. Arnold Shore says:

    Re “there’s no cylinder head”: True, but there’s two crankshafts. And compression ration can be whatever you want in a conventional engine; it’s set for the expected octane ratings in the available fuel.

    So why the hype if the advantages are real????

  2. Blaen says:


    That’s not true. With a normal engine, changing compression ratios dynamically is not possible. With the engine described, it can change compression ratios at will.

  3. Eric says:

    I wonder why Pinnacle isn’t going the whole way and building a prototype car? The engine is the hard part, the rest of it (body, chassis, trim) is very simple in comparison.

  4. Andreas R says:

    Saab developed a variable compression engine and implemented working prototypes which combined with a turbo gave high efficiency and octane tolerance.

    Ironically, GM scrapped the idea when they bought Saab.

  5. evo says:

    Slightly off-topic but hey… SAAB had a variable compression engine ( ) Even been tested in 9-5’s and than GM ditched it. Probably because size mattered to them… more than efficiency (and in the end power…)

    Ah.. somebody beat me to it ;)

  6. Sean says:

    Sounds like a Michael Moore documentary waiting to happen – anyone contacted the fellow, seriously?

  7. Mike Love says:

    I think if you view the animation : of its functioning you’ll see it all better. It’s incorrect to say “no cylinder head” it has valve mechanisms regulating flow…its simply integral to the main case/combustion chamber. It’s more of an engine inside out design. The key advantage as I see it is the higher Compression Ratio vs Stroke Length. This engine achieves the same CR with half the conventional stroke. This means less mechanical stress, higher RPM possibilities, better vibrational characteristics since its inherently self balancing in each bore, etc. It also may be possible to affect dynamic CR is by changing the valve timings, without the necessity of changing the base volumes swept per stroke. Otherwise it would require the central case/combustion chamber volume be changed to suit the fuel and applicaton.

  8. Larry Steiner says:

    Radical New Design? Variable compression ratio may be of advantage but Fairbanks Morse built OP engines for years. It’s not really that radical or new.

  9. That was very well written and thanks very much for the info! I’ve been searching for quite some time but it’s hard to find quality content. Keep up the good work!

  10. Ian says:

    Best of luck with your endeavors in Asia. If only the big auto makers in North America didn’t have that not invented here hang up the tax payers might not have had to bail them out a few years back