EcoMotors OPOC Two Stroke Engines – Opposed Piston Opposed Cylinder

EcoMotors OPOC 2 stroke engine

EcoMotors Opposed Piston Opposed Cylinder 2 stroke engine

Two stroke engines are favorites of everyone who wants a really compact engine with lots of power, there are fewer parts and power delivery on every stroke. Of course, the blue haze from the exhaust didn't sit well with the enviro-police so they've pretty much disappeared from use in transportation, but, they are slipping back with new technology applied to the new designs.

EcoMotors has a design called OPOC, Opposed Piston Opposed Cylinder. The design is just what it says, as you can see above, with 2 cylinders and 4 pistons. Peter Hofbauer came up with the idea when he was at Volkswagen, the outboard pistons take the place of the cylinder head and each piston only travels half the distance necessary for the full stroke, allowing higher engine speeds. An electrically controlled turbocharger can be used when necessary with adjustable boost, it can even spin up before the engine starts to give instant boost.

The engine can be built in a modular fashion, allowing more cylinders to be added in pairs with a clutch between the modules so one pair can be used at start or light load with the clutch adding more cylinders when required.

Emissions are said to be very low, meeting EPA standards for both gasoline and diesel configurations.

They're looking for 100 mpg in an automotive application, so just think what you could do with something like this in a motorcycle. Very cool!

(I actually thought I wrote about this engine before but found nothing, probably one of those engines I meant to post that got lost in my stack of post it notes carefully organized filing system)

Link: EcoMotors via New York Times
Related: Two Stroke Shop 1100GP
Related: JJ2S X4500 2 stroke
Related: Pivotal Piston water cooled 2 stroke

Additional Update: Several comments are saying this is not a new design. If you followed the link to EcoMotors I originally included, you would see the designer acknowledges that and refers to a WWII German aero engine from Junkers as one example.

Kim Scholer, comments below he sent me an article about an early NSU motorcycle powered by an engine like this. The article is completely in Danish, so I can't tell you anything else about it. The image is below:

NSU opposed piston motorcycle engine

The motorcycle is shown here but I can't quite figure how the engine is oriented. Perhaps Kim will be able to fill us in.

NSU opposed piston motorcycle

The point here is not that this design is entirely new, but, as I said in the first paragraph of the post, that technology is allowing us to utilize old concepts in new ways with low emissions and high power output. Computerized injection, electric turbochargers, clutches to gang modules together, all of these update the old idea into, essentially, a new engine based on what is obviously an older engine design. I think that's pretty neat.


  1. says

    Looks both plausable, and commercialy viable, ( read; affordable to build). Why is it that noboby has jumped on this attractive bandwagon? Powerful and light weight? Sounds like a winning motorcycle engine design to me. Go Fast. Ride Safe. Be Well, Mark.

  2. scritch says

    Looks cool, but wide. Not so much of a problem for cars, but bikes? Maybe a vee configuration would work? I’m not surprised that this idea is good. There have been opposed-piston diesels on submarines and locomotives for decades. There’s even one, called a “delta” design, that has three cranks with three sets of opposed pistons, all arranged in a triangle with the cranks at the apexes. Lots of power in a small (relatively) package.

  3. Patrick says

    Like the first two responses, the motor makes great sense. While the width may create packaging problems, the layout lowers the center of mass. One concern, however, is the thrust on the outboard pistons due to an offset rod. That seemingly has been addressed looking at the height of the skirt, and perhaps technology like the newer coatings (DLC?) might provide long life. Neat idea, maybe mounted lengthwise in a bike.

  4. Art says

    The concept/prototype is too big for a motorcycle, 40 inches long, weighing nearly 300 lbs dry, but still an intriguing idea.

    One inherent issue with small piston port engines as used in motorcycles was that inlet/exhaust timing was tied together via the crankshaft. The various contraptions devised to sidestep this limitation were ingenious, but still with limited gains and introducing other inherent flaws. This embodiment does not directly address this issue, as both pistons for each cylinder are directly driven by the crank shaft.

    This concept engine could be adapted where the “head” piston was cam driven and would control the inlet flow, with the geometry designed to hold/lock it nearly stationary in the power phase of the stroke. The “regular” piston would transmit combustion forces and would have the exhaust port. The head and regular piston could have different strokes/phasing, (or even different bores?) optimized between timing, intake/exhaust flow volumes and patterns, mass, force transmission and reciprocating balance considerations.

    Even if the head piston only reduced the regular piston’s stroke by 25%, just imagine… Looking at their animation, you can see ports ringing the bores, eliminating the problem of squeezing charge in and exhaust out through bore-restricted valves.

  5. Paulinator says

    The Junkers and Deltec opposed-piston designs have more crankshafts but fewer moving parts and smaller footprints (in locomotive terms).

    The very old split-cycle engine ties a pair of parallel cylinders to a common combustion chamber. A pair of “slightly out of phase” pistons are connected to one crank shaft and perform assymetric port timing in a kind of “Cross-flow” from one cylinder to the other. This design was used in bikes. I think Porche even played with the concept for Hitler’s “Peoples’ Car”.

  6. Tin Man 2 says

    Looks good to me, The Electric Turbo may help by acting as a variable intake control to increase flexibility and clean up emmissions. Dont count the IC engine out yet!!

  7. nortley says

    The OP engine was built here for decades by Fairbanks-Morse, but more simply than the Eco. I suppose it’s a trade off between two cranks and a bevel shaft or twice the connecting rods and reciprocating masses. Either way it just doesn’t look like it could be built light enough for a motorcycle. Now for the toy hauler….. With no valves to burn and sufficient port and piston cooling, one should be able to stuff in as much air as a turbo will push. So this engine could be a fun way to take one’s bikes to the track.

  8. says

    Before WW2 NSU built a 350 cc 2-cylinder motorcycle with double pistons, alled 351 L. It was a parallel twin with the cylinders longitudally in the frame. It worked ok, but the factory decided to go with a more conventional engine layout. As we can’t add pictures here, I’ve sent the article (in Danish, so good luck) to Paul Crowe.

  9. todd says

    It doesn’t look like it would have any side loading issues on the outboard pistons; they each have two connecting rods. Let’s see, that’s 6 rods for 4 pistons and 2 cylinders. Still pretty cool but I don’t see this as a high / variable RPM engine. More likely you would port it to run at a nice, low, fixed RPM where efficiencies can be maximized. At that point you’re now attaching it to an electric drive train to handle speed variations.


  10. Richard says

    It will be interesting to see the HP/TQ specifics on this smart design, but this reminds me of the Dyna Cam engine. Similar to using pistons moving back and forth in the cylinders of a revolver, the originals were used on torpedoes, weighed 25 lbs. and made something like 100 horsepower using benzene or some other nasty fuel. A modern airplane version made, if memory serves, 180 HP and like 1150 FT-lbs of torque. THAT might scale nicely down to 2 wheels!

  11. Simon says

    But how does this engine solve the oil problem? Does it have a separate lubrication system or must it still be mixed with fuel?
    As far as I know one of the major problems with emissions of two-strokes is the oil-fuel mix.

  12. Paulinator says

    Richard, I followed the Dyna-cam effort, too. I believe that it was killed by voracious piston skirt friction. All that massive torque was grounded by the sliding pistons against the bores. There are other barrel engines without that issue, however.

  13. Michael Purdy says

    Went to school as a Mechanic in for the USCG learned about these engines. all the previous opposed piston engines depended upon blowers to create the pressure in the cylinder. Just as old detroit diesles did. Cant see crankcase charging working here. Detroits and the Fairbanks-Morse engines use in subs and trains were forced asperation engines. I se the need for a supercharger or electric turbo.

  14. Michael Purdy says

    Simon, it apeers that it has a sump type lube system, 2 stroke does not require a mix if it is not a crankcase chared system.

  15. Michael Purdy says

    Art your comment made me think that the Fairbanks-Morse engine had a shorter stroke on the top piston as the design was usually a vertical cylinder, and the accual combustion chamber could be placed anywhere in the cylinder. Rotating and reciprical mass could be juggled to produce an infinite range of performance based on application.

  16. says

    I object to the comments that this is too big or too heavy for a motorcycle.

    The most talked about model is probably way too big and way to heavy — however, there are multiple versions of this engine. One such version is small and light enough to be held with one hand 13 pounds (!). The 13 pound version produces 13.5 horsepower (presumably at the crank). It measures 3.6 x 6.1 x 16.2 inches (without a transmission).

    See pictures here:

    The 450 pound version is listed on their website at 350+ horsepower, so it’s really not appropriate to compare it with traditional motorcycle engines in terms of size, weight, fuel consumption, or power.

    While many people feel 13.5 horsepower is not nearly enough to propel a “real” motorcycle, note that this has about 3 horsepower more than the motorcycle I ride and a fair amount more than the millions of Honda Cub/clone bikes on the roads around the world.

    It’s also worth noting that the small engine can also be paired for more power at [still] remarkably low weight.

  17. todd says

    There appears to be a wasted reciprocating volume in the “heads”. This could easily be used to charge the cylinder if a more simple, naturally aspirated version was desired. It would still require a small amount of fuel-borne lubrication for the rings though.


  18. Paulinator says

    Fifty million Honda Cubs have mechanized personal transport for emerging economies over the past half century. The bike is cheap (pronounced s i m p l e) and reliable (also pronounced s i m p l e). When service is required it usually takes place on a dirt floor in an ally with basic tools – the design tolerates those conditions and that is why it proliferated. Does the new OPOC engine fit that bill? Doesn’t look like it based on the exploded view.

    VW introduced the W 8 layout so that they could bundle 8 cylinders into a package the size of a typical 6. This OPOC design ignores physical constraints to persue other benefits. It also overlooks manufacturing and assembly issues, production cost, servicability…damn it must be really good where it counts.

  19. says

    @Paulinator, a Lifan 70cc replacement engine (similar to Honda Cub engine) weighs 42 pounds and puts out around 6 horsepower (not sure if that’s crank or RW).

    These OPOC engines have the potential to do significantly more horsepower with significantly less weight. That sounds pretty good to me.

    If more power isn’t necessary, then one could extrapolate than an even smaller version of the engine could be made to do less horsepower at an even more incredibly small weight.

    I’m not sure it’s really fair to judge the design based on its exploded diagram and animation. For that matter, I’m not sure the diagram of any engine would suggest that it could be disassembled and reassembled in a dirt alley without cause for worry.

  20. joe says

    This is by no means a new design ! In the 1950 and 60’s the design was used by a company called Roote’s who built hundreds of thousands of the two stroke diesel engines.They where incredably compact and put out good power ,and reved high. They where horizontal 3 cylinder units with six opposed pistons,3 fuel injectors,and a three element injection pump, with a Roots shart drive supercharger (blower ) fitted.Most where used in trucks,buses and boats.The down side was they screemed using higher rpm to develop full power.When larger mufflers where introduced to comply with noise output regulations ,the engine was choked and lossed power,so it was discontinued.With the aid of modern technology I can see why the design has been resurected.

  21. Art says

    As for the size of the current prototypes. Scaling down of engines usually results in lower percentage gains in areas like efficiency and power output. Scaling down normally only saves in materials, and may actually cost relatively more in manufacturing and providing easy maintenance. (A 600cc I4 engine costs about the same as a 1000cc one to produce, and a 250cc one perhaps even more. The internals of the Honda production 250-4 from the late 80’s(?) was described as “jewel like”) As an example, large marine engines often can completely disengage one cylinder to allow repairs while the rest of the engine runs. Not gonna see that in a motorcycle engine anytime soon. Just because it works on the larger scale doesn’t mean it will work as well in the smaller scale.

    There are probably a large number of practical reasons why this and similar larger engine designs have never been used in motorcycles and scooters, or even cars. Perhaps the latest electronic controls, materials and imminent reductions in fuel availability will make such designs practical alternatives. Only time and a lot of expensive experimentation/development will tell.

    @Michael Purdy,

    Yes, but I believe the F-M engine still ran crankshafts top and bottom and both handled power transmission. I haven’t seen any design where the “head” piston was cam driven (positive displacement, i.e. drum cam) and had no power transmission role. I was thinking that if the head piston was a very short stroke, moving only far enough to open a ring of ports and provide a small (less than 20%) compression assist it might be possible to take advantage of the best properties of piston port 2-stroke, OP and conventional engine designs.

    The electronically controlled, electric motor driven turbo charging as described is a great idea to sidestep the inherent issues with conventional mechanical turbo/super charging. Have the boost available when required, not locked to exhaust flow or crank revs.

  22. Paulinator says

    joe, in Tai Chung I saw a Sanyang scooter being “re-ringed” in a crude shop off an ally on a dirt floor at 11 in the evening.

    Can this new / old engine be made more clean and efficient and smooth and power-dense and S-I-M-P-L-E and practical than all other designs? With enough margin to invest the resouces? I hope so. I really really hope so.

    …but I doubt it.

  23. Art says

    There’s two main ways to approach “simple”. One way is designed to be manufactured and repaired using the lowest common denominator of materials, skills, state of tune etc. The very basic engines that can be re-ringed in a primitive shop in the middle of nowhere fit this model. There are situations where this is the best solution, bar none.

    The other side of “simple” is designs that may be very complex, but so well executed that they are easier to use and there is little or no “hardware” maintenance required over the expected life of the mechanism. A modern inline-4 sportbike comes to mind. I have rebuilt and maintained, at a serious hobby level, all manner of infernal combustion engines for over 30 years. Would I dive into a modern FI I-4 engine to refresh rings/bores/valves as I have on simpler designs in the past? Probably not. But then I doubt I will have to, given it will probably never see more than it’s 100,000 km design life. Even club raced in stock from-the-factory condition, these types of engines seldom fail from design or manufacturing issues. Simple to use, appropriate service life/efficiency/emissions, complicated to repair.

    I recently acquired an old Gold Wing with 250,000 km on it. It understandably needs a “freshen-up” to deal slight oil-burning and various niggling mechanical issues. A quarter million km with nothing beyond regular even though regular maintenance is not unusual for Wings. But you’re not going to re-ring this in a dirt-floor shop in a few hours. But did it owe the original owner much? Not by my reckoning.

    As to the age-old question, how much HP/torque is “needed” for a motorcycle application? A modern stock 600cc I-4 sportbike produces well over 100 RWHP into an approximately 400lbs wet package. More than most people “need” or want. Comparing apples, the CBR125-R (essentially 1/4 of the 600) produces about 13 CRANK HP into a 280 lb wet package. If you are expecting the “sport” CBR125R to do the same job as it’s 600cc RR (“race-ready”) sibling you’ll be disappointed. Is the CBR125R to be as easily field repairable as a Honda Cub? Not likely.

    But I’d bet the 600-RR with it’s full FI and stock catalytic converter is “cleaner” per HP produced around town than a carbureted Cub or especially my 3 HP 4-stroke flat-head lawnmower (at the track, all bets are off… the 600 is a pig at WFO throttle). So simple, low absolute fuel consumption and minimum emissions do not always lock together.

    I doubt there is any way the ECO Motor design as presented will compete with Honda Cubs and it’s legitimate and illegitimate progeny. The percentage gains in fuel economy and lowered emissions probably can’t justify the added complexity and subsequent cost, even if the power/weight can be scaled down. But it may be able in some form compete in motorcycle niches where more than “the minimum” is required or desired by the market. Whether those markets/niches will still exist in the future on a scale that they do now is open to a debate which won’t be solved here.

    So place yer bets and take yer chances. As presented, I really think the ECO has the best chance in cars, but maybe that’s just me not wanting to ride 1950’s performance-level/weight motorcycles, even if they are “clean”.

  24. nortley says

    That NSU looks like it may use half of the ECO engine, that is the crank and one cylinder assembly with its rods and pistons. It sits with the cylinder upright and has two cylinders with the crankshaft running fore and aft. It should be balanceable if the upper piston and rods can be kept really light to make up for their greater lenghts. Alternatively, and I would almost expect it of a German bike of that period as an experiment, make one cylinder the pumper and the other the burner. Sometimes looking at an old picture is as good as reading a whole book.

  25. says

    It seems there is much debate over whether the engine is too complex or not.

    It certainly is very complex — and with added complexity there is often public resistance and skepticism. If you didn’t like Honda’s water-cooled v-fours, or SOHC engines, or DOHC engines, or fuel injection, or four-stroke engines when they were new concepts…well, then it’s not surprising at all that you would be reluctant to put any faith in another design that seems quite complicated.

    The goal of this engine is definitely not to create the dumbest, simplest, cheapest ICE yet. I hope no one thinks that is the point.

    I can’t state the goal on the designers behalf, but it certainly seems they have succeeded in creating a flexible engine (in terms of fuel and layout) with an outstanding power-to-weight ratio (at least in the smaller engines, the larger version I think still has some proving to do). This is exactly what engine designers of all lineages have been trying to do for over 100 years. This is especially important in motorcycles — perhaps moreso than in any other application aside from airplanes.

    Another thing is fuel efficiency and pollution — it’s hard to say without concrete test data, but they claim it is an improvement over typical engines. What more is there to say? I don’t think there is good evidence to dispute that until more testing is done and made public.

    On the comment of a 600 being cleaner “per hp” than a Honda Cub…what? Does having more horsepower mean you use less fuel or go shorter distance? Measuring pollution/consumption per hp is ridiculous. That’s like suggesting a Hummer shouldn’t have to be tested by the EPA because it’s cooler than the other SUVs on the market.

    It’s true that low fuel consumption and low emissions do not always correlate — however, it’s impossible to have low emissions without low fuel consumption.

  26. Art says

    You take my comparison ad absurdium. Notice I was comparing the Cub and CBR600 on the street. At the same traffic dictated speeds and accelerations, the CBR’s FI and catalytic converter should produce less unwanted emissions than a carbureted Cub, as it doesn’t take much more produced HP to move the CBR than the Cub. Likewise, run a Cub WFO for a while and see how much the fuel economy suffers.

    Testing has been done that shows engine-driven lawn equipment to be the worst polluters by multiples over modern FI/electronically managed auto engines. The carbureted Cub (and the various cheap clones) is more closely equivalent performance/state-of-tune wise to lawn equipment than a modern FI engine, so maybe my premise is not so ridiculous.

    I think Hummers and all big-engine SUV-type personal-use vehicles are a waste of resources on so many levels, with virtually no redeeming factors and a needless danger to others in/on smaller vehicles. But that’s another rant.

  27. Paulinator says

    Thx Art, et al. I enjoy reading informed opinions from fresh perspectives.

    I am seriously interested in clean and s i m p l e ICE technology. I’ve prototyped a weed-whacker with assymetric port timing derived thru an oscillating / reciprocating piston. Yeah, it ran. It ran well!!! The design utilized 90 per-cent of the original 2-stroke engine parts (remember that production tooling and fixtures are a massive investment). Prior art made it a no-go, however.

    When I look at this effort I see a dogmatic adherance to a layout that is not elegant or beneficial enough to overcome inherent disadvantages. A boxer is good, therefore a boxer/boxer must be better? Time will tell.

  28. todd says

    From what I remember the NSU motors ran two pistons side-by-side with a common combustion chamber. As stated, one piston handled the intake, the other handled power and exhaust. I think it was referred to as a “twingle”, i.e. TWin/sINGLE. The pistons ran on a common crank throw but the offset of the two cylinders allowed the intake to open and close sooner for longer duration and less overlap. Puch, DKW, and TWN each had a version. Some motors had differing crankshaft orientations to the paired cylinders.

    BTW, the CUB / Lifan engine is weighed with an integral flywheel/clutch/gearbox/generator and it has been designed to be used as a partial structural member. The weight comparison with this motor is invalid as it has been designed as a suitcase generator.


  29. todd says

    did anyone else notice the 6 connecting rods run on a crank with only 2 mains? I wouldn’t expect this to run at continuous high, motorcycle type RPMs. Still pretty cool though.


  30. Scotduke says

    This is an interesting idea. If it’s tuned for low fuel consumption then power output could be raised to better suit use in a motorcycle. Surely a V-configuration could be used as well to better suit use in a motorcycle. I don’t think this is a complex engine.

    The old Deltic locomotives used in the UK had a great power curve and the engines were compact, but they were noisy, guzzled fuel and had poor emissions performance, as well as having a reputation for unreliability. New technology could certainly deal with the fuel consumption, noise and emissions. It’d remain to be seen whether the reliability of this two stroke engine would meet requirements.

    I can’t see volume car manufacturers being keen to switch tooling from four stroke engines to use this new two stroke. perhaps low volume car firms or some motorcycle manufacturers would take the plunge? I’ll watch it with interest.

    I remember the Dyna-cam engine and did wonder what’d happened to it – so thanks to those who mentioned the reasons for its demise.

  31. kim says

    Info about the NSU prototype:

    August 8 1922 engineer Otto Reitz joined NSU, made company develop 2-stroke motorcycles.

    One concept he worked on had two cylinders in line, and a total of 4 pistons and 6 conrods. It had an Amal carb and disc valve. An oil pump for lubricating bearings was placed up front.

    The engine is completely without vibration. (I visited a ship engine museum recently, and saw a one-cyl. Junkers mini-submarine engine; the guide placed a coin standing on its edge on top of the running engine, and it didn’t fall over.)

    The NSU 350 L pictured above managed 120 kph (about 75 mph), 62 mpg, but 0,6 litres of oil per 100 kilometres. Bhp increased from 15 to 17,5 during development period, making it faster than NSU’s other 350 cc motorcycles.

    The smaller displament NSUs like 175 Z and 201 sell well, and NSU decides to stick with well-known tech. Otto Reitz leaves NSU for TWN (and interesting work there) while W.W. Moore from Norton joins NSU.

    All info about this is from the new 200 page book ‘NSU Motorräder 1900 – 1945’.

  32. joe says

    An extremely lightweight opposed piston opposed cylinder (OPOC) engine has been developed under a Defense Advanced Research Projects Agency (DARPA) program. FEV and Advanced Propulsion Technologies (APT) were asked by the U.S. Army Tank Automotive Research Development and Engineering Center (TARDEC) to modify this engine for heavy-truck applications. Analyzing the two stroke scavenging, the side-injection combustion, and the structure of the key components shows the potential of the OPOC concept. It is predicted for the 465 kW (650 hp) OPOC truck engine. The OPOC engine was designed to be modular. Each module is self-contained and delivers 325 hp. The modules are connected together via the Modular Displacement Clutch, which synchronizes the modules for achieving even firing when both modules are functioning. With an optimized scavenging process, the special design features of the OPOC engine offer a significant step towards the potential of the two-stroke engine having double the power density of a four-stroke engine. An estimated 90% scavenging efficiency has been achieved with unique gas exchange characteristics of the OPOC engine and the use of an electric assisted turbocharger. The OPOC engine runs with almost two times the engine speed (3800 rpm) along with a large cylinder stroke (167.53 mm), as a result of the split stroke of the opposed piston structure. This also improves the power density by another factor of 2.

  33. Paulinator says

    And the winner is:pattakon. I’ve got to love all that nothingness plus normal aspiration, too.

  34. todd says

    Yeah Red, like that – except without the huge rocking couple it would have from those two crank webs.


  35. rafe03 says

    I seem to recall Doxford 3 cylinder opposed piston 2-stroke marine engines with 12 throws on the single crank. The bottom pistons had conrods onto the crank for the main power transmission. The top pistons had a yoke that picked up push pods (2) either side of the cylinder from 2 extra throws on the crank. The top & bottom pistons were slightly out of time (about 18 deg) so that exhaust ports opened first & intake ports closed last.
    has some good illustrations & discussions on various Opposed Piston Engines used in marine, avation, stationary, & vehicular duties. I never knew they were so common or so well developed.
    I don’t think thast it matters whether the idea is old or new. Development needs to be done before any proposal can be proven to sink or swim. And that costs money! Maybe a lot of money. Big companies are not stupid when it comes to new ideas, just prudent with their shareholders money.

  36. Benjamin says

    For retrofitting existing engines: Beare! Coz he is an Aussie!
    For sheer ingenuity, reduction of unnecessary components and future scaleability: PATTAKON FTW!!!!

    I can’t see how OPOC is a better design than Pattakon OPRE. More components for starters. Even though the pistons are smaller and lighter, the reciprocating masses are likely to be higher. Serviceability looks to be difficult. Also where are the running prototypes of the OPOC? Pattakon have numerous running demonstrations, there is no substitute for that. Plus they have ideas for halving the concept to make multi-cylinder engines with longer TDC dwell. Bring back the Commer with a big-bore Pattakon OPRE!!!

  37. todd says

    Ben, if I remember correctly, OPOC has been building these types of engines for US military for a few years now.


  38. Benjamin says

    I read that they were pitching the technology for US military, didn’t realise they actually succeeded. Either way I would really like to see one of these things running, yet there are no videos to be found.

  39. todd says

    I guess it’s gone now. There used to be a couple pages dedicated to showing the cartridge type suitcase generators. They fit inside an 19″ equipment rack were bridgeable and ran off diesel. Maybe they started getting too many public inquiries.


  40. zam says

    Kim, please send us the link on the NSU 350 cc 2-cylinder motorcycle with double pistons, alled 351 L. Same one you sent to Paul Crowe. Thanks. This one has got me intrigued. Very little info exists.

  41. Will13 says

    As the author stated, it’s great to see old ideas come back to life. The 1930s were a very productive time as far as engine designs go, and no doubt, Germany had several designs that were far ahead of their time.

    However, teknolaphex is spot on, in my opinion, with his comment. You can see for yourself at that Russ did a great design right here in America. He was even featured in Hot Rod magazine in the early 1950s, as a possible powerplant for land speed racing. It’s my understanding that he even advised Porsche in the 1960s on some of the designs they were working on.

    Both the OPOC and the Bourke engines have strong possibilities in the 21st Century, as the designs benefit from far fewer moving parts, modern light-weight metals, and offer the potential to burn fuels other than pump gasoline. All this and the added thrill of high rev action and potentially big horsepower numbers. Very, very cool indeed!

  42. Peter says

    This would make a good aero engine and opposed piston designs have a long history.
    The German Jumo designs of the 1930s had 10s of thousands of flight hours, used in JU88 bombers and transports in WW11. Development stopped when Turbo prop engines came along. At the moment there are two small opposed piston 100hp aero diesels in development a 2 cyl 4 piston and a 3 cyl 6 piston, both geared twin crank shaft designs like the Jumo. There are other 2 stroke aero diesels in development a 300hp 8 cyl 2 row radial which has about 1lb/hp a 200hp 4 cyl V4, a 120hp 3cyl inverted 2 stroke with poppet valve.

    All these designs have both a super & turbo charger to overcome the low rev problems with turbos. So one of the secret of this design is the electrically driven turbo. Which is copied from an idea from a Continental Aero engines design in the 1990s a 2 stroke design.
    This design being a 2 stroke it is like putting a 2 to 1 gearbox on a 4 and with the
    opposed pistons that is another 2 to 1 so 2000rpm is like a 4 at 8000rpm.

    Full power at such low revs is good on aero engines, as turning a prop over greater than 2700rpm gives problems, with prop tips going supersonic. The only problem is with the 325hp 2 cyl design, very large torque pulses, with the prop driving the engine 30% of the time, can give dangerous resonances, not good for prop life.
    On this design 4 cyl are a minimum, this would always give positive torque pulses and lower torque ripple per rev.

    For a diesel bike this would give the BMW boxer formate with good power output.

  43. Eric says

    I didn’t read all the comments, but this is a diesel engine. No oil fuel mixing. It’s also very simple. Far fewer moving parts than a 4 stroke engine. Crank, 6 rods, 4 pistons, blower. Probably some gear drive assembly out back for water pump, oil etc. This example is turbocharged also, but that is not necessary for operation. The parts in this design are just larger.

    Compare to a 4 stroke engine. valves, cams, rockers or cam followers, something to drive the cams, etc.

    The older detroit diesel 2 strokes engines have similar intake ports in the bottoms of the cylinder walls but with conventional exhaust valves. The DD 451 had a second set of ports in the cylinder wall for exhaust. It was an extremely smooth engine. Still had a cam to operate the fuel injectors.

  44. Eric Jameson says

    I am slightly confused – is the black-and-white picture immediately above the picture of the old NSU bike the old NSU’s engine or the OPOC engine? It appears identical to the OPOC engine.

  45. kim says

    Eric; The pic of the opposed piston version was probably only to make it easier to see how the concept works. The was no info in the article about its origins.