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New Toroidal Internal Combustion Engine Promises 20:1 Power-to-Weight Ratio

The Massive Yet Tiny (MYT) engine

A California inventor is developing a new compact and highly efficient engine—the Massive Yet Tiny (MYT) engine—that promises high power output with a very high power to weight ratio (20:1). The inventor, Raphial Morgado, recently won first prize in the 2005 Emhart-NASA Tech Briefs Design Contest for his work on the engine.

The engine moves pistons on different rotors relative to each other to form combustion chambers of variable volume in a toroidal cylinder. The pistons move in stepwise fashion, with the pistons on one rotor travelling a predetermined distance while the pistons on the other rotor remain substantially stationary.

Fuel is drawn into a chamber as one of the pistons defining the chamber moves away from the other, and then compressed as the second piston moves toward the first.

The cycles of the MYT engine. Click to enlarge.

Combustion of the fuel drives the first piston away from the second, and the spent gases are then expelled from the chamber by the second piston moving again toward the first. An output shaft is connected to the rotors in such manner that the shaft rotates continuously while the rotors and pistons move in their stepwise fashion.

The engine fires 16 times on one revolution of the crankshaft, 32 times on two. By comparison, a standard V8 fires four times per crankshaft revolution—one-quarter the number of the MYT. Angel Labs, the company developing the engine, calculates the equivalent displacement of the MYT as 848 cubic inches (13.9 liters), with a 3-inch bore and a 3.75-inch stroke. The company further calculates that the 14" x 14", 150-pound prototype could produce power in excess of 3,000 hp.

[The 3,000 hp rating] is conservatively estimated from 850 CID. A conventional engine can produce 4 hp per CID (when turbo charged). Four times 850 [the equivalent displacement] is more than 3,000. Our data of air motoring (800 lb.ft. of torque from 150 psi of compressed air) extrapolates to more than 4,000 lb.ft. of torque when fuel is ignited, exceeding our conservative estimate.

—Jin K. Kim, Managing Member, Angel Labs

The design is also modular. Additional MYT units can be connected by removing the rear cover of the engine and connecting another ME chamber assembly. With a dual-assembly configuration, the engine becomes a “64-cylinder” engine with 1,695 cubic inches displacement (27.8 liters), raising the power-to-weight ratio up to a projected 40:1.

The engine uses only about 20% of the number of parts normally found in a reciprocating internal combustion engine, and only 12 of the MYT parts are moving parts, reducing friction and parasitic losses.

Unlike a reciprocating combustion engine, the MYT engine permits a piston dwell at the equivalent of Top Dead Center (TDC)—the starting point for combustion. The current prototype is set for a piston dwell of approximately 12 degrees of the crankshaft rotation. By adding in that delay under combustion before permitting the power stroke, the MYT burns a greater percentage of the fuel and air mixture in the combustion chamber, resulting in a more complete combustion.

All we know is that 12-degrees dwell at the TDC, which no other engine can do, will burn all the fuels completely. Therefore, we expect very clean emissions.

—Jin K. Kim

Other features of the engine include:

  • The ability to support a compression ratio as high as 70:1.

  • No valves. The MYT uses open ports with no restriction. Airflow action is one way.

  • The entire engine acts as a heat sink and a radiator. It is both air and oil cooled.

  • There is no thrust loading on piston skirts.

  • Pistons do not touch the cylinder walls, only the rings do.

  • Pistons travel only the same direction. No reciprocation, only stop and go.

  • There are no cylinder heads, no cam shaft, no valves (the ME is equivalent to the bottom end of a reciprocating engine).

  • Intake compression and power stroke and exhaust stroke events are happening all at the same time, so there are no load strokes.

The MYT engine is not the first implementation of rotating pistons in a toroidal cylinder—the 1968 Tschudi engine is very similar in concept. (A newer derivative is by Hoose, 2005.) The key to the MYT engine is its timing mechanism.

The stop and go actions can be generated in many different ways, but you can not have active locking mechanism, because it will break under repeated stress. It took Raphial, who usually can invent in a couple of hours per invention, more than two years to come up with this invention (he threw away about 10 different ways of implementation.)

—Jin Kim, in the Angel Labs forum

Angel Labs is targeting a number of application: autombiles and trucks, pumps and compressors, aviation (helicopter, fixed wing and UAV), and military. Their goal is to license the technology non-exclusively to everyone. According to Jin Kim, Angel Labs is currently in discussions with Lockheed Margin, Boeing, Ford and several smaller potential licensees.

(A hat-tip to Bob C!)




If this is really practical, the applications for light aircraft should be huge.

Harvey D.

Could it be used for a much lighter weight genset for PHEVs?

John Allison

What is power to weight ratio of other ICEs? 20:1 is a nice ratio but i would like something in which to compare.


I note that this engine has only been run with compressed air, not on a combustion cycle.  This means that the following are not characterized yet:

  • Mechanical loading of the various mechanisms (including the stop/start system).
  • Stress on the cooling system.
  • Thermal efficiency.
This thing sounds a lot like the next Wankel, and could have problems of its own.  Let's wait and see before gushing over it.  That said, 40 HP/lb puts it into territory where it competes with gas turbines!


Er, even 20 HP/lb does.

The state of the art in auto engines is about 100 HP/liter for high performance models (about 1.6 HP per cubic inch).  I can't tell you what the typical power/weight is for cars, but for opposed-piston light aircraft engines it is about 0.5 HP per pound.


Sounds like a bunch of hot air to me. These "im going to revolutionize the internal combusition engine" ideas come out of nowhere every 5 minutes. They haven't even run the engine with fuel yet. Just compressed air so don't hold your breath.


Looks much like the Sarich Orbital engine:

This is what happened to it:


Trying to get electronics TSO'd for aircraft use is enough of a headache. I could just imagine what he will have to go through to get a brand new powerplant certified for aviation use.


"...that promises high power output with a very high power to weight ratio (20:1)."
Sorry but as long as power and weight are not expressed in the same units, such a sentence is pure nonsense. I would certainly never trust an inventor who is not even able to use proper terms to describe his "discovery".


I'm supposed to know a little bit about mechanics. This thing is greek to me.

I don't know greek.


Given that it is an American inventor I would hazard a guess that they are saying 20hp to 1lb, but that is only specualtion since it isn't explicitly defined.

I believe the LS1 from GM weighs ~400-450lbs and developed 400hp in Z06 form that would give 1hp per lb but that is with emissions equipment (catalytic converters & mufflers), emissions requirements and driven accessories. Until they have this engine running in an EPA lab to ascertain compliance with automotive emissions standards the power it produces can't be compared.

For example: A drag car from Puerto Rico, known as Sakura, was running mid 7 second 1/4 mile times using a 2.6L 4 cylinder turbocharged engine developing somewhere around 1000hp (the motor used with turbocharger weighed around 350lbs) but don't expect that engine to meet emissions standards for noise or air.


If this thing can really pull this kind of power to weight ratio, maybe I can finally get a flying car in my lifetime. It looks like this prototype runs on diesel as well - I wonder what the thermodynamic efficiency of this motor will end up being.


Well, if you read the article, you would see that the claim was 150Lbs and 3000hp.

20hp : 1Lbs

Modern high output street legal engines Are between 1:1 HP:Lbs and 1.5. (Some bike engines offer 2:1 but not for very long :)

Someone earlier mentioned HP/Liter, but that is a measurment not useful for anything but marketing.
It bears no relivance to HP:Weight, nor reliability, nor thermal efficiency or emissions. It is a moron's litmus test.

This engine is potentially exciting, but I agree with previous posts, I want to see it run on a fuel, and I have doubts about 150Lbs worth of material handeling the stresses from 3000hp, or even half of that.

tom deplume

Consider this. 3000hp is over 7,500,000 btus/hr. If this engine is a very good 50% efficient a very small surface area would need to dissipate this much heat every hour. The surface temp may need to be over 1000F. Skepticism is very much in order.

Barry R. Guthrie

I agree Tom,

With this much heat thermal cooling is a big problem.
I'm not sure how they are going to achieve good combustion in only 90 degrees CA. This is too short even with hydrogen. The exhaust heat losses will be very high and reduce the thermal efficney. I'm not sure how they are also achieving a high compression ratio with this configuration.

The engine has high surface area for the outer housing this will disapate much of the heat and lower the thermal efficiency. The cooling the center rotor will be a big problem.

You also have a strange split line running down the center of the combustion chamber that separates the two different rotor groups of four. This split line will be prone to combustion gas penetration, especially at very high compression ratios.

How does this keep the combustion rotation in the desired direction? It looks like it would just produce center pressure that would go both forward and backward.

I think that they use some elaborate gearing system, but this will add friction and be prone to wear. This will add to the reduction of the brake thermal efficiency.

You might somehow get high power density, but you won't be able to maintain it for very long due to the thermal loading and you certainly won't get very good fuel efficiency from high surface heat and exhaust losses. This would be something that the military might try, but I can't see what it will do to help reduce our oil and fuel consumption.


This invention rings in very high on my "baloney" meter. Conceptually, toroidal combustion engines that work on the basic principles noted here have been around since the 1920s. See: U.S. Patent #1329625. Their theoretically high power-to-weight ratio is not a new discovery.

Plenty of inventors have been at work over the years trying to come up with improvements in design to make such an engine practicable (you can search the patent records for for examples), which it does not yet seem to be. If Mazda was willing to give the Wankel engine a try back when, I find it hard to believe that they did not stumble upon the toroidal concept and decline to pursue it for good reasons.

Reading between the lines, it seems that if anything new has been invented here, it would be some sort of stop-and-go mechanism, to get the variable speed piston movements needed for the concept to work. Not surprisingly, they disclose virutally nothing about the actual mechanics of that system, though I imagine that likely involves elliptical gearings linked to the central shaft(s), or some such.

What really limits engines of this sort is not the lack of a clever mechanical solution to the piston timing and speed issues, but the fundamental materials science problems that previous postings have identified: heat exchange, sealing the piston walls and toroidal assembly, building an assembly strong enough to withstand the forces generated by the production of that much power in that small a space, etc. I also notice that no mention is made of its fuel economy, and would tend to believe that it would not be good for very fundamental physical reasons.

I would be surprised if this amounts to anything more than an attempt to get misguided investors to put money into a venture of dubious merit.

Roger Pham

Hmmm, power to weight ratio is 20hp/lb,eh? This proves that the inventor of this thing is an idiot when it comes to material science. Power is force times distance. Aluminum, Titanium and Steel can withstand certain amount of stress before they will break. The best heat engine (Diesel) is around 50% thermal efficient. This means that a lot of heat will need to be ejected from the engine before it will melt. A race-car engine is at the forefront of power-to-weight ratio, and at no more than 3hp/lb ratio, the limiting factor here is metallurgy, as the material cannot handle any more heat nor stress. A race car engine must be rebuilt after every race. A Wankel rotary engine is even simpler than the toroidal engine and it has no reciprocating parts, either, and a good Wankel engine has about 1hp/lb to 2hp/lb, no more.


It would be great if this engine had said power to weight ratio; however, I have to remain a skeptic. If you take a look at some of the other advanced rotary engines that have recently come out you will find that they do not get anywhere near such figures. The design that comes to mind is the randcam engine that has many more power pulses per rotation in a compact and efficient design. They are getting great numbers, but they are nowhere near what this gentleman is claiming. Also, on paper the randcam seems to be a better design, but I may be wrong. I have not done an in depth review of either engine. Another thing to consider that pumping efficiency does not necessarily translate into the efficiency of the engine with the complete combustion cycle. Combustion efficiency is quite different. I read through some of the discussions on the MYT engine site and as I recall there was a question posed as to why they had not run combustion test. I encourage you to go to the source to get the reply 100% correct; however, I recall it being to the effect that they did not want to damage the engine as they had experienced damage in a previous combustion test. If such is the case they may indeed have problems with the engine parts being able to withstand the stress of the process. I have to admit that this design is quite interesting. I wish them the best of success. I hope they overcome all of their engineering hurdles. Don't we all?


This design does have better thermal properties than the Wankel; the ratio of surface to volume is much lower, and there appears to be no period where the intake and exhaust are interconnected.  The big issue appears to be the mechanical arrangements for moving the vanes.

This may have more potential as a topping cycle for gas turbines than as a stand-alone engine.  In a gas turbine, combustion occurs at constant pressure and the gases expand, increasing entropy.  Now consider a gas turbine blowing through an engine like this, running at 1:1 compression ratio and a larger expansion ratio.  The fuel would burn in a closed chamber and the gases would increase in pressure, deriving work from the expansion before being released to run the turbine.  An adiabatic engine built with silicon carbide combustion-chamber surfaces could eliminate most need for cooling, too.

If a gas turbine could get an extra 3:1 pressure ratio in the expansion stage, it would improve the efficiency considerably.  It would also let the turbine idle with much lower fuel consumption, as the compressor would not be required to generate sufficient pressure to keep the engine operating.

Roger Pham

The thermal problem of this engine is pale in comparison to the sealing problem for this engine, since the power can be scaled back to reduce heat. The most fundamental problem is the sealing of the cut out in the donut hole that may render it totally impractical. This is because there is no piston rod on the underside of the piston, so the pistons must transfer their power laterally to the engine shaft through a cut out groove around the donut hole, as the pistons move circularly in the toroidal cylinder. Now, imagine trying to seal this groove against leak of oil and hot exhaust gas. The sealing problem of the Wankel is pale in comparison to this problem.
No, Ceramics like silicon carbide, are brittle, and would not be a good idea here due to the rapid changing in temperature in the combustion chamber, hence tremendous heat stress, leading to cracking. Metal can withstand temperature changes much better. Gas turbine blades would be much better candidate for ceramic due to the lack of sudden temperature variation. Even metallic high-temp nickel alloy of gas turbine blades does not like rapid temperature change, either, and so, turbine engines are limited to a finite number of cycles of throttling up and down in a jet aircraft.


This design has MUCH worse thermal efficienies vs a Wankel, Engineer-poet, at least as described: the "dwell" of 12-degrees means the effective engine surface area at it's "TDC" is probably doubled, and since that is the point of highest temp/pressure, it'd have roughly twice the energy loss from heat as a conventional engine.

That 12-degree also reduces the angular distance for getting a good expansion ratio. If they were able to reduce the "dwell" and increase the expansion ratio, though, perhaps the efficienies would come back up. However, the reason they probably won't be able to, if they manage to build one, is that they have a terrible arrangement for the flame kernal at the spark plug. It's at the cylinder wall!! They'd get terrible incomplete combustion without the dwell, I'd imagine. And it gets worse: the gap of the plug can't extend into the swept area at all(!!) - so the rings will be going over a gap, which is not possible with current ring technology... you'll get immediate wear and strain to the rings.

The other problem to the rings & sealing is that the "cylinder wall" halves are moving in relation to each other, meaning these would have to be sealed to each other, which would be a HUGE source of friction that isn't mentioned. In an ICE, piston/cylinder wall friction is about 70% of total friction, but in this engine it'd be under 50% because of the addition in the friction from one-half of the cylinder wall to the other!!

Several technical points of the article are in error, under "features":

1. There is no way a gasoline engine can reach 70:1... and it's not a diesel since I see spark plugs. People have worked on high-compression gas-detonation engines, but this design isn't suited for it with its sealing issues.

2. Open ports with no restriction is not a benefit (one-way airflow is, though). I've seen the data from Lotus's cam-less high-pressure hydraulic valvetrain, which can mimic any profile, even square-wave... open values with a square-wave, though, and they actually have worse airflow. I also believe (though it's not mentioned) that this would be a very low-rpm, low-mean-piston-speed engine, so to salvage air-flow with some fancy variable-length-runner intake system may be difficult, due to the extreme length of the runners required. Probably measured in feet, not inches.

3. Air/Oil cooled? Are you kidding me. Everyone has already pointed out extreme cooling a 3000hp 150lb engine would require... of course what we really want is a 300hp 50lb version, I guess, but either way cooling requirements are basically bhp over thermal efficieny, so you'd need a larger cooling system than a normal 300hp engine, not a smaller/non-existant one.

4. No thrust loading?? Ok, take a bucket of water, and swing it over your head on a rope... do you feel loading on your arm? These piston skirts will as well... its centrifugal. There should be much less than the load caused by the kinematics of a connecting rod, especially if this is a low-rpm engine, but it's not zero.

5. Pistons don't touch the cylinder walls? Please. See #4

6. No reciprocation? The momentum loss in a "stop and go" system described here is EXACTLY equal to the momentum loss in a reciprocating engine, so this is technically accurate, but of exactly ZERO benefit.

7. There 6th bullet point is actually somewhat correct, cheers!

8. They almost had a run, there! But no... while it's true all the strokes happen simultaneously, this is not a benefit... because there are a lot of off-axis forces because every-other piston is moving together, but adjacent pistons are moving with opposing motions, and extreme & opposing forces. Note that the "upper cylinder head" function is being performed by the bottom-half of the trailing piston!! so these forces will require extremely robust construction, perhaps heavier-duty than a convention ICE engine that has seperate power/intake/etc strokes.

However overall, not having looked at the patents yet, and seen the air-engine demo, won't write this off yet. Well, I'll write it off for fuel efficiency and clean-burning, but if the sealing, intake, and combustion issues can be overcome, which is certainly possible, it would be very compact for it's power output, if not for it's weight. That is useful in some applications - tanks, airplanes, etc.

And it is original, at least to a wankel/orbital... I haven't looked at the referenced patents from '69 though, but even if it's not completely original to those patents, at least those patents have long expired.

Good luck to them I guess. Most of the errors I pointed out are just on people writing articles about engines who aren't engine people, or haven't thought through their own inventions I guess.



Sorry for the typos above. It occurs to me you could fix the spark plug problems I mentioned above, by housing the spark plug _inside_ the pistons, which would position the plug properly, and leave no gap in the cylinder wall to give the rings problems. You should be able to wire/insulate the plug through the attachment of the piston to the power transmission ring (maybe). Kills 2 birds with one stone. Hmm, if that is an original idea, maybe I shouldn't have disclosed it here. *wink* *wink*



Under the hood of almost all modern automobiles there sits a four-stroke internal combustion engine (ICE). Though the efficiency of the design has been improved upon significantly in the intervening years, the basic concept is the same today as that used by the first practical four-stroke engine built in the 1870s...But the automotive industry may soon be revolutionized by a new six-stroke design which adds a second power stroke, resulting in a much more efficient and less polluting alternative.
...After the exhaust cycles out of the chamber, rather than squirting more fuel and air into the chamber, his design injects ordinary water. Inside the extremely hot chamber, the water immediately turns to steam– expanding to 1600 times its volume– which forces the piston down for a second power stroke. Another exhaust cycle pushes the steam out of the chamber, and then the six-stroke cycle begins again.

The Six-Stroke Engine


Kevin:  without more info on the mechanisms (as opposed to the combustion chamber) of the toroidal engine, it's hard to conclude that it's either great or fatally flawed.  Besides, there are lots of ways to alter the other pieces while leaving the basics more or less the same.  And I don't see sealing as the big issue you do; inertial forces are never going to force a vane against the wall as they do in a piston engine, so the seals can be built with very different mechanical properties which would not work (or even survive) as piston rings.

CharlesWT:  I saw that too.  I'm not sure if it has a future, but if it does it's going to need a second exhaust valve for the steam stroke, a separate manifold for steam and a condenser.

Roger Pham

Thanks, Kevin for a thorough analysis, and especially in explaining that the two cylinder halves are moving against each other. I kept thinking erroneously that some kind of transverse cut out at the center of the torus allows the pistons to transmit their force to the center shaft. Now, then, the issue is even more interesting:
1) For the kind of pressure involved in generating decent horsepower in a IC engine, a cylinder half will be pushed away from the other half with the greatest of force. Let's say 500-600 psi at the end of combustion point, then the cylinder halves are pushed away from each other with forces of thousands of pounds. Now, let's see what kind of seal and lubrication would be able to hold up against that kind of force in that kind of heat without breaking down and excessive wear? not to mention heavy construction need at the junction of the seal, causing high inertial mass that must be stopped and go continously, thus accelerating the wear on the gearing mechanism that allows such a weird motion to occur. In a standard piston Otto-cycle engine, the piston pin and crankshaft are also exposed to high force right at the point of combustion, but the difference is that the piston pin and crankshaft are protected from the extreme combustion heat so that the oil won't get degraded, and that they are generously lubricated by fresh oil forced in under high pressure.
2) Dwell time of 12 degrees for complete combustion? Pure fantasy. This much time and 3000-5000 degrees F of heat generated and tremendous amount of force necessary to restrain the piston movement until the dwell time is over means tremendous thermal stress and mechanical stress on all the involved parts, such that, if this design will ever work at all, it won't last very long. How long can one expose lubricant to extreme heat of 3000 degrees F?
If you think that Wankel engine is having problem with rotor seal and efficiency, don't look toward this new design for salvation.
GOOD LUCK, MYT engine and Raphial Morgado, you are gonna need a lot of it!!!

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