The two-stroke gasoline engine was once a marvel of engineering, offering up huge doses of power in small and lightweight packages. Unfortunately, gas two-strokes also burn oil by design, making them a dirty proposition in today’s world. One startup company thinks that it not only has a way to bring the two-stroke into the 21st century, but also make the engine of your dreams. The Alpha-Otto REV Force is a supercharged two-stroke engine that supposedly runs cleaner, makes tons of power, and will run on pretty much anything from gasoline and diesel to kerosene to hydrogen.
The spec sheet of the REV Force sounds too good to be true. The small 578cc engine weighs just 105 pounds and produces 173 HP. It has a supercharger, doesn’t burn oil, and is lubricated like a four-stroke engine. But the craziest part is a claim that this engine is so highly computerized that it can change compression, displacement, timing, and spark settings on the fly, allowing for the engine to burn darn near anything that will combust. Oh yeah, then there’s a claim about 50 percent thermal efficiency, which also sounds wild.
The REV Force sounds like something magical, like the kind of engine that any gearhead dreams about. This thing is a compact, parallel two-cylinder engine that looks like it can fit into a motorcycle, and its power-to-weight ratio sounds like it would make small cars tons of fun, too. But is this at all even possible? Or is this two-stroke just blowing smoke? Let’s look at the claims.
Alpha-Otto was formed in 2022 in Detroit by John L. Krzeminiski and David D. Dusseau. Krzeminiski is an engineer who has built up a ton of experience working for OEMs, including nine years at FCA/Stellantis, six years at Ford, and three years at FEV Group. Dusseau is a businessman with three decades of experience in managing and directing various technology firms. The company says one of its missions is to secure the future of the internal combustion engine by making one that can burn conventional fuels cleaner, and also be carbon-neutral.
Alpha-Otto has been marketing its potential advancements in ICE technology since 2022, but the company didn’t get media attention about it until this year, when Alpha-Otto began publishing videos showing the prototype engine actually running. These videos look impressive, too, and show the REV Force supposedly running a wide variety of fuels without modification:
Why Two-Strokes Aren’t As Popular Anymore
Two-stroke engines can still be found in use today. Lots of lawncare equipment still uses two-stroke engines, and you can also still find two-strokes powering dirt bikes, some scooters, some boats, and other limited applications. Certainly, the two-stroke is not nearly as ubiquitous as it used to be. You will not find a new two-stroke car for sale in America, and most heavy trucks on the road have been running four-stroke diesels for a while.
Earlier this month, I wrote about how the two-stroke engine has become more of a niche and a piece of history rather than a mainstream form of propulsion. In that piece, I explained how a four-stroke engine works:
During a single full cycle, an internal combustion engine must intake the fuel/air mixture, compress it, ignite it, and allow the exhaust gases created by ignition to escape. As their names imply, a four-stroke engine achieves this with four strokes of the piston, and a two-stroke does it all with just two.
In a four-stroke engine, the piston moves down during the intake cycle (that’s stroke one), pulling in a fresh air-fuel mixture. Then, the valves close and the piston moves up (stroke two), compressing the air-fuel mixture. Once the piston reaches the top of the cylinder, a spark plug ignites the mixture, starting the combustion cycle and sending the piston back down (stroke three). Finally, the piston heads up one more time (stroke four), sending exhaust gases out of the exhaust valve. You only get power every other time the piston reaches the top of the cylinder. Four-cycle diesels work in a similar way, but ignite their fuel through high compression rather than a spark plug.
Then, I explained how a basic two-stroke engine works:
Two-stroke engines combine multiple cycles into the same stroke of the piston. A two-stroke engine combines intake (“scavenging”) and compression into one stroke, then ignites the charge and exhausts it on the next stroke. Unlike a four-stroke and its every-other-stroke power delivery, with a two-stroke you get combustion and thus and power every time the piston reaches the top of the cylinder. The graphics above and below are from Yamaha, a brand once famous for its two-stroke motorcycles.
Critical to this process, at least in the most basic crankcase-aspirated two-strokes, is the operation of the ports. The exhaust port is exposed during the power stroke, and the exhaust begins to exit. As the piston continues down, a fresh air-fuel charge enters the combustion chamber from the crankcase through a transfer port. This charge helps push out the remaining exhaust gases while refilling the combustion chamber.
When the piston begins its upward movement again, the transfer port closes, the exhaust port closes, and the intake port opens. The movement of the piston forces the fresh charge in from the carburetor and into the crankcase, where it will wait for the engine to fire, then to scavenge exhaust gases, and start the process over again. These ports, at least in a very basic two-stroke, aren’t actuated by a valvetrain like the valves in your car. Instead, the movement of the piston is what either closes or opens the ports.
The easy way to remember the difference between a two-stroke and a four-stroke is that a four-stroke fires every second time the piston reaches top dead center, while a two-stroke fires every single time the piston reaches the same position. Two-stroke engines are known for their power density, peaky power bands, and high power-to-weight ratios. Other positives include the fact that basic two-strokes are ridiculously easy to repair and that two-strokes have a distinctive engine note.
One of the biggest challenges faced in the engineering of two-stroke engines is limiting losses during scavenging. In a basic two-stroke, the incoming air-fuel mixture charge is used to push out burned gases. However, this process is lossy, and unburned mixes get exhausted out of the tailpipe, as I note from my piece:
The scavenging process is also one of the two-stroke’s biggest problems. Some unburned fuel is lost during the scavenging process and is sent out through the exhaust, which is bad for the environment. As Cycle World notes, a crankcase-scavenged two-stroke like the one I described above may waste 30 percent more fuel compared to an equivalent four-stroke. The publication correctly points out that such waste would be unacceptable today. However, in decades past, it was seen as a worthwhile trade-off as two-strokes often weighed 40 percent less, had less bulk, and made more than enough power for everything from lawncare equipment to boats.
As Cycle World notes, it wasn’t long before engineers all over the world had discovered a funny limitation in the basic two-stroke motorcycle engines of the 1940s. Cylinder pressure had to be just low enough so that the cylinder would fill itself with a fresh charge when the transfer port opened. Since an early two-stroke’s ports were opened by the movement of the piston, this was achieved by having the exhaust port open sooner. Boom, cylinder pressure drops enough to begin scavenging.
However, the twist is that due to not having any real control over the port, making it open sooner also meant that it would close later than desired. So, the fresh charge would have more time to scavenge, and thus, more fresh fuel would be lost. These limitations meant that the low-displacement motorcycle two-strokes of the 1940s often made single-digit horsepower. If only there were a way to control when to open and close the ports without depending on the position of the piston.
The basic design of what could be considered the “modern” two-stroke dates back well over a century, and since then, two-stroke variations have gone in all sorts of different directions in efforts to produce more power, reduce losses, and improve reliability.
According to Cycle World, the problem of timing the opening and closing of the ports had a neat solution in the form of the rotary disc valve. This part, which consisted of a crankshaft-driven disc with a hole in it, allowed for asymmetrical timing of the ports, which allowed for even greater power numbers. Rotary discs and reed valves were also a solution to one of the two-stroke’s other problems: losing some of the fresh air-fuel-oil charge back through the intake during scavenging.
Oh, and the problem with losing some of the fresh charge through the exhaust? That has a pretty neat fix, too. As Cycle World writes, in late 1951, DKW engineer Erich Wolf was experimenting with two-stroke exhausts. He knew that valves wouldn’t move fast enough to prevent fresh mixture losses during scavenging. In his research, he found that if he used the exhaust pipe design to create a positive pressure exhaust wave, the wave can be used to act like an exhaust valve, keeping the fresh charge in the combustion chamber.
I’ve written about other advanced two-stroke designs, including the Commer TS3 and Napier Deltic diesels. Many two-stroke engines throughout history do not use their crankcase for aspiration, and instead may use a combination of fuel injectors and/or Roots-type blowers.
Technically, two-strokes still have advantages today. They can still build mountains of power with peaky torque curves and do so in small packages. Two-strokes are still beloved by many today, as well. However, a challenge of making a modern two-stroke is getting it to comply with modern emissions, as two-strokes still burn oil, and there are still at least some losses of unburned charges through the exhaust port. Even the expansion chamber exhaust noted above isn’t perfect at the job. Likewise, a high-performance two-stroke may have somewhat short intervals between major services.
Some awesome advancements have been made here, including fuel injection. For example, motorcycle manufacturer KTM has what it calls Transfer-Port Injection, which uses a fuel injector located behind the transfer port. KTM also has Throttle-Body Injection, which places the injector in the throttle body. In both cases, KTM can achieve a cleaner burn than the old carburetor setup thanks to more modern tech. Bimota famously tried out two-stroke fuel injection decades ago.
This finally brings us back to Alpha-Otto, which is proposing one of the biggest advancements to two-strokes yet.
The REV Force
Alpha-Otto is claiming to have improved the modern two-stroke in a number of key ways.
One of the biggest changes is the inclusion of an electric rotary valve in the engine’s exhaust port. As I noted above, various two-stroke designs have had rotary valve intake discs for a century now. Powered two-stroke exhaust valves are a newer technology, with Honda, Kawasaki, Suzuki, and Yamaha having each experimented with changing exhaust timing through powered exhaust valves in decades past.
In theory, putting a rotary valve here can not only prevent air-fuel mixture losses, but allow for more flexibility in timing. To Alpha-Otto, this whole rotary exhaust valve deal is so important to the development of the engine that the engine gets the first half of its name, “REV,” from “Rotary Exhaust Valve.”
Alright, that’s pretty neat. Next, Alpha-Otto also changes the two-stroke configuration by deleting the transfer port and repositioning the intake. The REV Force engine does not get its air-fuel mixture from the crankcase, and thus, the fresh charge does not need to have oil to lubricate the engine. Instead, the crankcase can be filled with oil, like you’d get in a four-stroke. Likewise, the air-fuel mixture now no longer has oil in it, which is a positive for cleaner burning. However, the REV Force is still a two-stroke at heart because it fires every time the piston reaches top dead center.
A basic two-stroke uses the piston to draw in a fresh charge, but this design doesn’t really allow that. So, that’s where the supercharger comes in, and it controls the air going into the engine and handles the pumping that the piston would normally have to do.
If this sounds familiar to you, it’s because it’s very close to how two-cycle diesels work. Except in this case, the REV Force is using a rotary exhaust valve rather than the poppet valves and valvetrains often found in two-cycle diesels. Alpha-Otto is going with this configuration because rotary valves have a greater airflow capacity than poppet valves. They’re also simpler to implement, leading to less weight. In other words, the belief is that the rotary exhaust valve is better for performance.
Alpha-Otto’s next change comes in the form of fuel injection. This is important because while the rotary valve is decent at reducing unburned fuel losses, it’s not perfect. If the incoming charge of air from the supercharger becomes infused with fuel, some would be lost during scavenging. However, adding fuel injection means that the fuel can be squirted in after the rotary exhaust valve is closed, and thus no unburned fuel would be lost.
Alpha-Otto’s functioning prototype is a water-cooled 578cc twin and has been run up to 220 HP and 130 lb-ft of torque. It measures 15 inches long, 13.7 inches wide, and 11.8 inches tall, has a static compression ratio of 10:1, and has been tested up to 7,000 RPM. The production model is supposed to redline at 8,000 RPM. Alpha-Otto says the expectation is a time between overhauls (TBO) of around 2,000 hours.
Finally, Alpha-Otto claims that since the rotary exhaust valve, supercharger, and fuel injection are all computer-controlled, it allows the REV Force to change timing and compression on the fly. As a result, the engine is supposedly capable of running everything from gasoline and diesel to hydrogen and compressed natural gas, and pretty much most burnable fuels in between.
To put it all together, the Alpha-Otto REV Force is more or less promising to have the big power of a small two-stroke with the reliability and emissions of a four-stroke, with the added fun of the flexibility of a multi-fuel engine. I told you that this engine is trying to be the stuff of dreams here.
Alpha-Otto sees itself putting these engines into stationary industrial equipment first, like generators. Later, it wants to target the transportation space. Could we see a REV Force-powered motorcycle or car?
The Next Steps
Well, the answer is that I’m not sure. On one hand, it’s awesome that Alpha-Otto has a working prototype of its engine. However, there are tons of steps between making a proof of concept and actually putting said concept into production. Those steps require lots of money.
Alpha-Otto is currently relying on crowdfunding and other investments for the next stage of its development, and has thus far earned $571,909 from its current WeFunder campaign. The company said that it had $25,622 in cash on hand as of June 2025 and had previously received $1.2 million in federal grant money. According to the crowdfunding campaign, Alpha-Otto expects to need around $3 million over the next three to five years. After that point, the company is hoping to turn a profit. There is no hard release date for the engine at this time.
Alpha-Otto also hasn’t released information such as the emissions or fuel economy of the engine, either. But that stuff aside, it does seem like what Alpha-Otto is doing here is technically possible. The company isn’t inventing new technology, just using existing two-stroke technology in different ways, and then adding a multi-fuel spin to it. So, it’s not really magic.
That said, I do have one concern, and it’s the expected TBO of 2,000 hours. Alpha-Otto says that this is about twice as good as the TBO of an older high-performance two-stroke, which seems about right. This is about the TBO of a high-performance four-stroke used in powersports, like an engine from Rotax. However, a 2,000-hour TBO would seem incompatible for use in a car. It wouldn’t even work that well for a commuter motorcycle.
The emissions question aside, there are other unanswered questions like how much this engine would cost, and whether OEMs are even interested in a new two-stroke design in an era where EVs are trying their hardest to take over. The practicality of hydrogen is extremely limited in many regions, too. Of course, Alpha-Otto also still needs money to put it into production in the first place. I’m skeptical about this, but I suppose we’ll see.
So, there are lots of important questions that remain, but I do like the concept, at least. I love the idea of a two-stroke engine that will run on whatever is the cheapest fuel at the gas station. I adore the idea of two-strokes making a comeback. But these are mammoth promises for a startup company to fulfill, so who knows? At the very least, I’ll be watching this unfold.
Top Image: Alpha-Otto
The rotary barrel exhaust valve will absolutely be this engine’s undoing. So many people and companies have tried to make rotary engine valves work, and they’ve all failed. For the valve to seal it will need tight precision tolerances and constant lubrication to prevent excessive wear. That’s just inherently incompatible with hot exhaust gasses loaded with carbon always flying through it.
Shoot, race engines using barrel/rotary throttle bodies that only move 90° open/close have a hard enough time keeping them sealed and operating properly, let alone something spinning around at engine speed.
The rotary disc intake valve on two-strokes, made famous by Rotax (and others), didn’t have to deal with hot exhaust gas, and was constantly being bathed in lubricating oil from the incoming air/fuel/oil mix.
Despite many advantages in 4-strokes, AFAIK, rotary valves have never made it to market because nobody has been able to solve the issue of sealing. How would this be different? (Crowd sourcing: harvesting money from dupes.)
ME: ChatGPT, turn this headline into snark about heat engines or the 2nd law of thermodynamics
ChatGPT:
“This Wild Supercharged Two-Stroke Engine Promises to Run on Gas, Diesel, or Hydrogen — But Still Can’t Outrun the Second Law of Thermodynamics.”
“Runs on Gas, Diesel, or Hydrogen — Still Converts Most of That to Heat, As Ordered by the Second Law.”
“This Engine Eats Anything — and, Like All Heat Engines, Still Belches Out Entropy for Dessert.”
ME: More sarcasm
ChatGPT:
“This Supercharged Two-Stroke Will Burn Anything You Feed It — Except the Laws of Thermodynamics.”
“Runs on Gas, Diesel, or Hydrogen — Miraculously Still Manages to Waste Energy Like a Champ.”
“Bold New Engine Claims Fuel Flexibility; Still 100% Compliant With the Second Law’s Strict No-Fun Policy.”
“Will Run on Anything! Except Hope, Dreams, or an Efficient Carnot Cycle.”
“This Engine Might Burn Three Fuels, But It Still Can’t Cheat Physics — Nice Try, Though.”
Thought I would give this a go and then use the first result to enable my favourite ChatGPT prompt.
“Because who needs the 2nd law of thermodynamics when you’ve got a wild supercharged two-stroke that runs on gas, diesel, or hydrogen — apparently defying efficiency and sanity all at once.”
More nihilistic.
“This wild supercharged two-stroke prototype runs on gas, diesel, or hydrogen—because why bother respecting the 2nd law of thermodynamics when entropy’s already winning and nothing really matters anyway?”
MORE!
“This wild supercharged two-stroke runs on gas, diesel, or hydrogen—because in the end, the 2nd law of thermodynamics will reduce it all to meaningless heat death, so why not burn every fuel possible before oblivion wins?”
Ahhh, much better.
I can think of many VW owners that wish they could go 2,000 hours between engine rebuilds… at an average of 50MPH that’s 100K miles 🙂
Also, what does a rebuild entail? Is it more complicated than changing the timing belt guides in a Mercedes V8 or a V10TDI that may be a 40 hour job, or more like what can be done to a Honda where in about 5 hours you can replace everything but the block without taking the block out of the car? If everything that needs servicing is easily accessible a full rebuild may end up cheaper and faster than replacing spark plugs on some transverse V6 crossovers simply because you can reach it.
“Sounds like something magical” could have been this entire article. Every few years some group claims to have revolutionized internal combustion and every time it comes back as either a series of wild math errors, an earnest but poorly funded daydream, or an outright scam. Often all of those things in sequence. This thing would be fun if it was a youtube video of someone’s hobby, but it’s very silly that anyone at the company or in the press imagines it might amount to anything more than a pleasant diversion.
The tricky part about 2 strokes in modern applications is aftertreatment compatibility. Engine oil in the exhaust poisons catalysts, making them inert and thus not able to do their job of converting the harmful constituents of exhaust gas into harmless stuff (NOx into nitrogen, CO and hydrocarbons into CO2, things like that). All engines burn a little bit of oil, but 2 strokes tend to burn quite a bit more than 4 strokes for a simple and frustratingly difficult to solve reason – the piston rings must travel past the exhaust port, so any of the oil that they are scraping back down into the crankcase can go out the exhaust. Many companies (see Achates for one example that has gotten pretty far down the industrialization track) have tried to fix this with very precisely controlled lubrication of the cylinders, trick materials on the cylinder walls and piston rings, all sorts of neat stuff – but the fact remains that the 2 strokes will pass more oil out the exhaust than 4 strokes.
If they can fix that issue, then they have something marketable on their hands. Otherwise this will be another engine tech that, best case, will be limited to niche applications like military, drones, stationary off-road use, or other scenarios where they can either pass more lax emissions regs, or side step them completely.
First question with any alternative valve design, how does it handle carbon build up? Second question, how well does it hold tolerance? Apparently they’re saying, good for 2000hrs.
Think we will see better BEV options to keep them ahead.
Cool concept.
Won’t be productionized unless purchased by a larger engine Tier 1 manufacturer, which is a lot harder than it sounds.
“However, a 2,000-hour TBO would seem incompatible for use in a car. It wouldn’t even work that well for a commuter motorcycle.”
That would be fine for an EV range extender though.
My thoughts exactly. How did this article about “REV” make it past the gauntlet of EREV disciples of the Autopian staff? It’s only one letter off!
Someone who obviously regrets switching to decaf this morning.
I’m disappointed that the image doesn’t say 2 stroke of genius, but I do find this whole thing interesting. That 2000 hr issue might make this a versatile choice for an EREV that’s expected to be on battery most of the time, but I don’t know how you’d make that work right and how much consumers would buy in. It’d certainly be messy for warranty.
Cool idea, though.
Think of how much more powerful this engine would be if the pistons were dimpled!
What’s the typical use case for this thing? 2000hrs TBO makes this a disposable engine in consumer applications. I guess for emergency generators that don’t get used regularly it might work? but why reinvent the wheel nobody was asking to be reinvented?
Unless this is also magically quieter than a 4 stroke I wouldn’t want it powering a generator outside my bedroom window.
Drones. High dollar military and border patrol drones with long ranges and high loiter times. Same as LiquidPiston.
I predict it will revolutionize the 3 wheeled flying car market.
Finally, an engine for my Elio!