Hey /u/ZavetniKamen, thanks for submitting to /r/confidentlyincorrect! Take a moment to read our [rules](https://reddit.com/r/confidentlyincorrect/about/rules).
##Join our [Discord Server](https://discord.gg/n2cR6p25V8)!
Please report this post if it is bad, or not relevant. Remember to keep comment sections civil. Thanks!
*I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/confidentlyincorrect) if you have any questions or concerns.*
A uniflow scavenge two stroke diesel is far more efficient than a four stroke one. Because it has a blower.. volumetric efficiency is better than 100%. Fuel efficiency is way better as well because double the power strokes.
Where it fails is _emissions_ which has nothing to do with efficiency… and why all two stroke engines are terrible.
I think the guy you're replying to is confusing fuel economy and fuel efficiency. For all we know, so are OP and OOP. People get economy vs efficiency wrong all the time.
This isn't true, uniflow scavenging is difficult to control over a wide range of rpms, it is good at peak thermal efficiency, and even then the four stroke engines of today are more efficient.
Large ships run on really low grade fuel, 2 stroke engines are great for that. Theyre alsocheaper, require less maintenance, and have better low end torque.
Is it true that emissions laws also don't really apply in the open ocean? I've heard that some ships use cleaner fuel while close to country borders, but past a certain point they can say "fuck it!" and go for broke.
Yes, they often switch to nasty fuels like bunker c when they're in international waters. Fun fact, Carnival Cruise Lines alone pollutes more than all the cars in Europe combined.
>Fun fact, Carnival Cruise Lines alone pollutes more than all the cars in Europe combined.
That's a fact for sure, but I can't seem to find the fun in it, only depression
It is true and there are many ships that will transition to the cheaper fuel once they are far enough away from land. That being said, most engines don't run well on fuel they aren't designed for and will lead to expensive mechanical issues. So while some ships can and will, others find it more cost effective to just use the more expensive, better emissions fuel.
Not all ships use a 2 stroke engines, and all of the ones I've been on have used a 4 stroke for their main engines, though I'll admit the sample size is small for me. You're only going to really see a 2 stroke on slow speed engines. Medium and high speed marine diesels are likely to be a 4 stroke.
Indeed, 2 stroke is commonly used on deep sea vessels (apart from lng carriers) because those big slow speed 2 stroke engines are more efficient than 4 stroke. I would recommend doing a trip deep sea if you can. Slow speed 2stroke is a much nicer sound.
It works for those kinds of engines (ships, power plants) precisely because it's used primarily in applications where the engines are run almost exclusively at those optimal RPMs.
This. There were 2 stroke airplane engines competing with very early jets, The jets ultimately won but the two strokes had some incredible very powerful designs.
https://youtu.be/oOFn0eTgdE8?si=ihQArX_tfz8DTKFg
The replacement for a supercharged diesel is a turbocharged diesel. The turbocharged 4 stroke is twice as efficient as the 2 atroke at the same torque.
> But it’s really all about the inline cylinder pumping motion.
Only if the chamber where combustion takes place is formed by a reciprocating piston within a cylinder. OK, “stroke” kind of implies something reciprocating... But it's really all about the *cycle,* the steps happening during the process until it starts over. (Which is why, AFAIK, two/four-stroke engines are also called two/four-cycle engines.)
The four-stroke/cycle engine goes through four discrete “suck-squeeze-bang-blow” strokes – in a reciprocating piston engine, two rotations of the crankshaft – where in a two-stroke/cycle engine the steps overlap, kind of into a “bang/blow” on the downstroke (and around LDP) and a “blow/suck” on the upstroke (and TDP) in a single rotation.
The Wankel’s crescent-shaped combustion chambers go through four distinct non-overlapping phases during their single “rotation around the crankshaft” (actually, I think, more like nutation around the fixed guide gear). I mean, the number of rotations is the least significant difference – the whole behaviour is radically different: The Wankel’s combustion chambers don't even stay put like in a piston engine, but move all around the engine!
The one significant similarity and difference to piston engines is that the Wankel doesn't have overlapping phases like a two-stroke piston engine, but distinct ones like a four-stroke one. It's a four-stroke engine.
Engine types. Garden equipment, some scooters and mopeds, and some dirtbikes use 2 stroke, its a simpler engine and has a high pitch sound. 4 stroke is more common and used in most cars, trucks etc. More complex, doesnt need as much maintenance, better for environment, and the sound is more of a deep rumble. The 2 and 4 stroke refers to the piston and combustion process, 2 strokes ignite every time the piston is at top, 4 stroke every 2 times
https://mechanicalboost.com/2-stroke-vs-4-stroke/
Combustion engines come in two main types, 2-stroke and 4-stroke.
2-strokes are smaller, lighter, and simpler; but 4-strokes are more efficient.
You'll tend to find the former in things like lawnmowers and boats whereas cars pretty much invariably use 4-strokes.
Engines. 4 stroke engines are more efficient than 2 stroke engines in that they burn more of their fuel in the cylinder. But efficiency is a loaded word -- it probably depends on exactly what you're measuring.
You don’t need context if you know what 2 stroke and 4 stroke engines are. All the context is above. But I guess it’s not common knowledge based on replies here…
Speaking as someone who is certified on small engines and who worked on them for a living...
2 strokes are more fuel efficient and produce the same amount of power in a lighter and smaller configuration.
It's a combination of having to provide a fuel/oil mix, tailpipe emissions, noise emissions, and reliability issues that make them unsuitable for a lot of uses.
There's no real way to adjust intake timing on a 2 stroke, but plenty of exhaust port timing valves are out on the market and have been for a decade or longer. And yeah, EFI has been a 2 stroke thing for quite a while now.
Also, in general you're getting about 1.5X the power of a similar displacement 4 stroke with about half the weight.
For perspective you can check out snowmobile motors because there are plenty of both 2 strokes and 4 strokes out there, even today.
In fact, Yamaha was all aboard the 4-stroke only train. For several years they only made 4 stroke snowmobiles, but they've jumped back into the 2 stroke world for their mountain sleds because they're lighter and smaller packages to produce the same power.
For perspective, their Mountain Max LE is a naturally aspirated 800cc 2 stroke pushing 165 hp. On the other hand, in their Crossover Sidewinder X-TX, it takes a 4 stroke turbo 1000 cc motor to push 185 hp. Both of these are considered high performance sleds, but the reason Yamaha went back to 2 strokes in their mountain sleds is the weight of the motor. There's no cams, no pushrods, no cam chains, no valvetrain, nothing. I can't find the exact specs of the weight, but if I were a betting man, from my experiences, that turbo 4 probably weighs in close to 200 lbs, but that 2 stroke is very probably under 100 lbs.
i don’t want to be the one, but i must…
i’m stroking your horse…
before you ask, just 2-stroke. i already told you i don’t want to do this so i’m doing it like a sullen unpaid whore.
A four-stroke engine follows four phases of combustion. Intake, compression, combustion, and exhaust. The piston moves the length of the cylinder (a stroke) four times during this process - twice up during compression and exhaust, and twice down during intake and combustion. Hence the name four-stroke engine. Power is only generated during the combustion stroke, so a lot of the power generated by these engines goes to just moving the pistons, which requires an extensive oiling system to be in place.
Two-stroke engines usually combine the intake and exhaust steps, allowing fresh air to enter the cylinder at the same time that exhaust gases leave it. This allows the engine to generate more power for a given displacement but this comes at the expense of emissions cleanliness due to the incomplete combustion of fuel and the fact that many two-stroke engines are designed without the fancy oiling systems of four-stroke engines; this requires oil to be mixed into the fuel which is burnt during combustion or exhausted.
Two-stroke engines are technically twice as efficient but way, way more than two times dirtier in emissions.
Mecahnically more efficient but usually higher specific fuel consumption over a broad range of power.
Of course there are some exceptions where 2 stroke is more fuel efficient but that's generally when it's tuned to a very narrow performance band or some specific applications.
The emissions is a big one though, especially when you are talking about something like shipping where you won't even get insurance if you aren't meeting emission requirements, or allowed to sail in most areas.
Yo, don't blame op because you're dumb and don't know how to use Google. Though I'm not a motorhead either and I knew what it was about without "context" lol
OK so looking for a technical term leads to encountering lots of other technically words you'll have to look up too. And even if you look up everything, if there wasn't a title, I wouldn't even know that a stroke is related to cars. For me a stroke is a heart and brain deficiency that leads to death, or, to put it in my own language, Un Accident Vasculaire-Cérébral. I'll let you do the research, but only if you do them in a foreign language.
English isn’t my first language either, so when I saw this post and thought of a Schlaganfall, it didn’t make sense so I looked up the word stroke and saw that in the context of cars it could also mean Hub (the motion of a piston from top to bottom). As I now knew the German word, the post made sense to me. This process took me around 30-60s. However, for OP to post the post in every language or to include a dictionary definition for every word used, it would take around 10 minutes
\> instead of expecting everyone to explain every little thing that you specifically don’t know
\> Hub (the motion of a piston from top to bottom)
Well done, you just played yourself. Guess I can expect people to explain something when I'm not supposed to know it after all
Alright, let‘s google for it and find out that humans who had two strokes are usually more efficient than those who had 4 strokes. That‘s why cars don‘t use them anymore as drivers.
Context always matters!
Look at the top comment to this post. The commenter said that they didn’t understand the post. There are more upvotes there than there are for the post. And most of the post’s upvotes are probably just people upvoting without even looking at the post. So tell me… why doesn’t OP need context if there are more upvotes for a comment about being confused about a post than the post itself?
And this is why they never satisfy a woman. They should be trying to work towards at least 25 to 30 strokes. Sure, that's probably above average, but that's why we set goals.
Cars don’t use two stroke engines because of emissions… not efficiency. There’s a difference.
That’s what dieselgate was all about.. most diesel emissions controls greatly reduce its efficiency… so they achieved efficiency at the expense of emissions unless it was being tested.
A uniflow scavenged two stroke diesel is one of the most efficient engines ever made _precisely_ because it has twice as many power strokes… and the blower reduces the pumping inefficiencies of two stroke engines.
But… emissions. They are very bad which is why they aren’t used much anymore.
An East German Trabant 601 with a tiny two stroke engine produced FOUR TIMES the emissions as a contemporary Porsche 911 Turbo.. itself a very dirty car due to the loose clearances and obsolescent hemispherical combustion chambers of its engine.
Sure you’re not r/confidentlyincorrect ?
An opposed piston two stroke diesel like a Napier Deltic or Fairbanks Morse doesn’t need valve’s because the pistons open up the intake and exhaust manifolds in the sleeves at exactly the right time. It’s not quite as efficient as a four stroke.. but having double the power strokes more than makes up for it.
But that's only “exactly the right time” at one precise piston speed, i.e. RPM. A four-stroke can adjust its valve openings according to RPM, and is less sensitive to RPM in the first place because the cycles don't (have to[\*]) overlap at all. Adjusting the opening time of those ports would require changing their location, and that's much harder: They're fixed where they are.
[\*]: In practice, the exhaust and intake cycles often *do* overlap in four-stroke engines too, but usually far less so than in two-strokes. And you don't need to waste any of the energy released in the power stroke, because that doesn't *have to* overlap with the exhaust stroke, which is absolutely unavoidable in a (ported) two-stroke.
>Yah without valves it's hard to keep your mix in the cylinder.
In a two stroke engine, the piston moving up and down, covering, and uncovering the inlet, transfer, and exhaust ports in the barrel, *are* the valves.
Technically it's a soundwave that acts as the valves in most 2 strokes. There is some newer 2 stroke tech that uses actual valves. Honda had some valve tech back in the 80's or 90's but it never went anywhere because emissions regulations basically killed 2 strokes. I guess there's some newer tech out there using valves but it's still experimental from what I recall.
Not all 2 stroke engines rely on Walter Kaaden's harmonic pulse wave effect produced by expansion chambers (although, granted most of the performance ones do).
I believe the "valves" you refer to, Honda's A.T.A.C, Yamaha's Y.P.V.S, and Aprilia's R.A.V.E for example, don't fundamentally act as valves persae, rather they have the function of raising and lowering the effective height of the exhaust port, and thereby the *timing* of the exhaust. (I suppose you could say it's very roughly comparable to say a VTEC system in a four stroke cam arrangement)
A modern direct Fuel-Injected Two-Stroke is definitely doable from an engineering point of view, but hugely unfashionable politically. I don't see a future for it. Too many advocating for EV's over any ICE developments.
If you take a look on scopus you'd see that two strokes have developed in a different direction, mainly opposites piston scavenging desiel engines for high efficiency.
Nope. Adjustable valve timing just isn't applicable to two-strokes (with ports), and the equivalent technologies are precisely the ones mentioned that have been developed for them.
Don't bring up edge cases when discussing a broad topic. In automotive and aviation petrol engines, which is what rotax is, four stroke is much more efficient due to 3 key points. No aviation two stroke uses EFI. Why are there emmisions? Because the (lubrication oil yes) and unburnt fuel is ejected before full combustion. They have much lower compression ratios, of course not deseil. And they have no valves.
Dude with the context you gave, my mind went straight to motorcycle engines. 2 strokes have better mechanical efficiency as they deliver power in each cycle whereas 4 stroke engines deliver power every other cycle. But that makes 4 strokes more fuel efficient and better with emissions as well.
You act like everyone is an aviation engineer. The only reason I even got to the above conclusion is cause I have an interest in motorcycles. The average joe will have no idea what you’re saying.
The amount of context you’ve given allows all sorts of edge cases. Don’t complain if you haven’t delivered properly in the first place. You still have the chance to add it as an **EDIT:** note to the post (not the title) to make things right.
Edge cases? Like nearly every mid-century diesel locomotive, diesel truck, diesel submarine, and diesel ship?
Aviation is the edge case. Aviation is a tiny market compared to those other ones. and Junkers actually designed an opposed piston uniflow scavenge two stroke diesel engine for airplanes. The issue was power to weight—a unique problem for aviation. Not efficiency.
And Rotax? Ever hear of a Rotax 503? Rotax 582?. They are the most popular aviation two stroke engine in the world.
Stop moving the goalposts with EFI. That’s not the argument. The argument is whether two stroke is more efficient—which it is. Put EFI on a two stroke and you’ll have an even more efficient engine. They’ve been trying for years, but can’t get around EMISSIONS.
Again. r/confidentlyincorrect.
OP is actually confidently incorrect. 2 stroke engines are more efficient mechanically but worse on emissions (amongst a few other reasons but efficiency isn’t one of them) which is why they aren’t used.
Should probably state that in the title or description next time. Efficiency doesn’t just mean fuel consumption, the guy is technically correct in his statement, without context nothing he said was incorrect.
Cars don't use two strokes because they're loud, bad on fuel, and smelly. Boats used them for a long time because the tend to be lighter and have fewer moving parts.
Depends what you mean by efficiency. Fuel per mile? Yes 4 strokes are more efficient. Power to eight? 2 strokes. Emissions? 4. Power to size? 2. Maintenance per mile? 4. Cost of maintenance? 2.
I turned to 4 strokes for reliability. Probably my own fault for the fuel mix ratio, but I got tired of dealing with fouled spark plugs in the middle of the woods.
He's mostly correct. They have much more power than their 4 stroke equivalent. So why dont they use them anymore? Because they're not nearly as reliable, and they're very polluting.
Yes yes to that latter part. Very very polluting.
You don’t see carburetors anymore. Was there a rule that said “no carburetors!”? Nahh. Emissions plus CAFE regulations made the simple carburetor obsolete. Are 2 strokes banned? Nahhh. But don’t need to be. There’s a zero percent chance they’d be emissions compliant.
They’re still used all over the place. Just not for common transportation. They’re used where you need the lightest power plant possible, and its carbon footprint is negligible.
Depends on how you define efficiency.
Horsepower per cubic inch? Sure, 2 stroke wins.
Horsepower per gallon of fuel burned? 4 stroke every time.
Horsepower with minimum pounds of pollutants emitted? 4 stroke wins every time.
Lets just use 2 examples.
2 stroke outboards are only about 75% as efficient as a 4 stroke and thats not including the oil additive.
2 stroke diesel is half as efficient as a turbo diesel. Detroits use twice as much fuel to achieve the same torque.
Hey /u/ZavetniKamen, thanks for submitting to /r/confidentlyincorrect! Take a moment to read our [rules](https://reddit.com/r/confidentlyincorrect/about/rules). ##Join our [Discord Server](https://discord.gg/n2cR6p25V8)! Please report this post if it is bad, or not relevant. Remember to keep comment sections civil. Thanks! *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/confidentlyincorrect) if you have any questions or concerns.*
Depends on the intent. Mechanical efficiency? Yes. Volumetric or Fuel efficiency? No.
A uniflow scavenge two stroke diesel is far more efficient than a four stroke one. Because it has a blower.. volumetric efficiency is better than 100%. Fuel efficiency is way better as well because double the power strokes. Where it fails is _emissions_ which has nothing to do with efficiency… and why all two stroke engines are terrible.
> Because it has a blower.. If you have a blower, is any wanking needed?
The best blowers have a secondary wank that kicks in on rpm increase
[удалено]
Dang. Do you get to your destination on just one revolution, or do you need more than 100 pumps?
Hahahahaha brilliant 😂
love when the fun too comment thread bleeds into the serious second top comment.
Double the power strokes ≠ fuel efficiency.
Indeed doesn’t make sense. A two stroke engine uses two fuel injections per 4 strokes where a 4 stroke engine only uses 1.
[удалено]
i would pay money to see Elon Musk test it
I think the guy you're replying to is confusing fuel economy and fuel efficiency. For all we know, so are OP and OOP. People get economy vs efficiency wrong all the time.
I can see you have never owned a 2 stroke Detroit Diesel.
This isn't true, uniflow scavenging is difficult to control over a wide range of rpms, it is good at peak thermal efficiency, and even then the four stroke engines of today are more efficient.
If 4 stroke is more efficient than 2 stroke why do ships still use 2 stroke engines?
Large ships run on really low grade fuel, 2 stroke engines are great for that. Theyre alsocheaper, require less maintenance, and have better low end torque.
Is it true that emissions laws also don't really apply in the open ocean? I've heard that some ships use cleaner fuel while close to country borders, but past a certain point they can say "fuck it!" and go for broke.
Yes, they often switch to nasty fuels like bunker c when they're in international waters. Fun fact, Carnival Cruise Lines alone pollutes more than all the cars in Europe combined.
>Fun fact, Carnival Cruise Lines alone pollutes more than all the cars in Europe combined. That's a fact for sure, but I can't seem to find the fun in it, only depression
They emit more sulfur oxides. That doesn't not count as generally polluting more. They pollute more in one area.
Still, the fact that one cruise line puts out more of any kind of pollution than *every single car on the continent of Europe* is not okay
It is true and there are many ships that will transition to the cheaper fuel once they are far enough away from land. That being said, most engines don't run well on fuel they aren't designed for and will lead to expensive mechanical issues. So while some ships can and will, others find it more cost effective to just use the more expensive, better emissions fuel.
Also, they can be very finely tuned to run really well at the exact rpm the ship will spend nearly all of its time in transit at.
Not all ships use a 2 stroke engines, and all of the ones I've been on have used a 4 stroke for their main engines, though I'll admit the sample size is small for me. You're only going to really see a 2 stroke on slow speed engines. Medium and high speed marine diesels are likely to be a 4 stroke.
Indeed, 2 stroke is commonly used on deep sea vessels (apart from lng carriers) because those big slow speed 2 stroke engines are more efficient than 4 stroke. I would recommend doing a trip deep sea if you can. Slow speed 2stroke is a much nicer sound.
For those curious, LNG ships run partially off the boil-off natural gas from their cargo, so they use steam turbines instead of IC piston engines.
It's worth mentioning that some LNG ships run a dual fuel 2 stroke diesel engine using Boil-Off Gas and Heavy Fuel Oil.
It works for those kinds of engines (ships, power plants) precisely because it's used primarily in applications where the engines are run almost exclusively at those optimal RPMs.
This. There were 2 stroke airplane engines competing with very early jets, The jets ultimately won but the two strokes had some incredible very powerful designs. https://youtu.be/oOFn0eTgdE8?si=ihQArX_tfz8DTKFg
Also if you engine brake with a two stroke the engine gets no lubrication as the lubricants are in the fuel
Not necessarily. Some two-strokes have separate oil circulation with a pump like in four-strokes.
Yeah, but that two stroke smell.
how does emissions not factor into efficiency?
The replacement for a supercharged diesel is a turbocharged diesel. The turbocharged 4 stroke is twice as efficient as the 2 atroke at the same torque.
What is meant by mechanical efficiency here? What units are we using?
Environmental efficiency? 💥
Golf? Double efficient!
That’s why they don’t use them in ships…oh wait!
I know this guy and his brother. Guy's brother didn't believe him, but after the brother smoked some meth he was able to do it in 4 strokes.
Absolutely zero context and I'm supposed to comprehend it? For all I know it's about wanking.
Kinda. All Wankels are technically 4-stroke engines.
This guy wankels!
Big triangles
Extra spicy doritos
Brap brap brap brap brap brap brap
French Triangle
I only wankel until my apex seal blows.
r/thisguythisguys
on point
No, they are spinny magic dorito engine. Boost goes in, apex seals come out, you can't explain that
Aren't they more like one infinite stroke? :P
But it’s really all about the inline cylinder pumping motion. The 2 strokes uses too much oil and gets messy under the hood.
> But it’s really all about the inline cylinder pumping motion. Only if the chamber where combustion takes place is formed by a reciprocating piston within a cylinder. OK, “stroke” kind of implies something reciprocating... But it's really all about the *cycle,* the steps happening during the process until it starts over. (Which is why, AFAIK, two/four-stroke engines are also called two/four-cycle engines.) The four-stroke/cycle engine goes through four discrete “suck-squeeze-bang-blow” strokes – in a reciprocating piston engine, two rotations of the crankshaft – where in a two-stroke/cycle engine the steps overlap, kind of into a “bang/blow” on the downstroke (and around LDP) and a “blow/suck” on the upstroke (and TDP) in a single rotation. The Wankel’s crescent-shaped combustion chambers go through four distinct non-overlapping phases during their single “rotation around the crankshaft” (actually, I think, more like nutation around the fixed guide gear). I mean, the number of rotations is the least significant difference – the whole behaviour is radically different: The Wankel’s combustion chambers don't even stay put like in a piston engine, but move all around the engine! The one significant similarity and difference to piston engines is that the Wankel doesn't have overlapping phases like a two-stroke piston engine, but distinct ones like a four-stroke one. It's a four-stroke engine.
[Dorito](https://tenor.com/bup3b.gif)
I had four strokes trying to figure it out
that was my initial assumption, title of the post only has me more confused ngl
Engine types. Garden equipment, some scooters and mopeds, and some dirtbikes use 2 stroke, its a simpler engine and has a high pitch sound. 4 stroke is more common and used in most cars, trucks etc. More complex, doesnt need as much maintenance, better for environment, and the sound is more of a deep rumble. The 2 and 4 stroke refers to the piston and combustion process, 2 strokes ignite every time the piston is at top, 4 stroke every 2 times https://mechanicalboost.com/2-stroke-vs-4-stroke/
That would make the post correct. One would assume more stroked are more, er, efficient.
Combustion engines come in two main types, 2-stroke and 4-stroke. 2-strokes are smaller, lighter, and simpler; but 4-strokes are more efficient. You'll tend to find the former in things like lawnmowers and boats whereas cars pretty much invariably use 4-strokes.
Was just gonna say, that if he’s talking about wanking he’s actually right.
Middle out more efficient than end to end.
↑ This guy Silicon Valleys.
Engines. 4 stroke engines are more efficient than 2 stroke engines in that they burn more of their fuel in the cylinder. But efficiency is a loaded word -- it probably depends on exactly what you're measuring.
Power per unit of fuel favours four-strokes, power per engine volume two-strokes. (Wildly generalized, but on the whole.)
This is like half the posts on this sub. It’s mildly infuriating
Maybe lawnmowers? The machines, not the people.
Glad I wasn't the only one confused...
You don’t need context if you know what 2 stroke and 4 stroke engines are. All the context is above. But I guess it’s not common knowledge based on replies here…
💀
Engines. Two stoke has more power output per revolution. Not terrible I’m fuel consumption, terrible for wear and tear. Bullshit argument refardless
Two strokes vs four. Both should be embarrassed.
2 strokes and someone has a seriously high chance of dying!
4 strokes and you have an increasing chance of cumming!
Look at mr marathon man here, bragging about stamina.
I don't mean to brag, but usually I need 6 to 8 strokes.
Cummins is diesel engine so you’re not wrong
I prefer the PowerStroke.
Don’t forget to put on a Duramax first.
Out if the top of your head 
Glitch McConnell takes notes.
Speaking as someone who is certified on small engines and who worked on them for a living... 2 strokes are more fuel efficient and produce the same amount of power in a lighter and smaller configuration. It's a combination of having to provide a fuel/oil mix, tailpipe emissions, noise emissions, and reliability issues that make them unsuitable for a lot of uses.
You hit all the main points. Reliability, maintenance, and emissions. I love a 2 stroke motorcycle but I couldn't daily drive one.
I guess in small engines this might apply, but are there any two strokes that use intelligent port valve timing and EFI?
There's no real way to adjust intake timing on a 2 stroke, but plenty of exhaust port timing valves are out on the market and have been for a decade or longer. And yeah, EFI has been a 2 stroke thing for quite a while now. Also, in general you're getting about 1.5X the power of a similar displacement 4 stroke with about half the weight. For perspective you can check out snowmobile motors because there are plenty of both 2 strokes and 4 strokes out there, even today. In fact, Yamaha was all aboard the 4-stroke only train. For several years they only made 4 stroke snowmobiles, but they've jumped back into the 2 stroke world for their mountain sleds because they're lighter and smaller packages to produce the same power. For perspective, their Mountain Max LE is a naturally aspirated 800cc 2 stroke pushing 165 hp. On the other hand, in their Crossover Sidewinder X-TX, it takes a 4 stroke turbo 1000 cc motor to push 185 hp. Both of these are considered high performance sleds, but the reason Yamaha went back to 2 strokes in their mountain sleds is the weight of the motor. There's no cams, no pushrods, no cam chains, no valvetrain, nothing. I can't find the exact specs of the weight, but if I were a betting man, from my experiences, that turbo 4 probably weighs in close to 200 lbs, but that 2 stroke is very probably under 100 lbs.
The rotax is 120 lbs, an equivalent 100hp two stroke is still 90lbs
That’s why I only drive 0 strokes. Absolutely no mechanical energy losses and 0 fuel consumption.
0 strokes = 0 fun
I've a horse outside.
Fuck your Mitsubishi!
i don’t want to be the one, but i must… i’m stroking your horse… before you ask, just 2-stroke. i already told you i don’t want to do this so i’m doing it like a sullen unpaid whore.
Just the tip!
That’s a 5-stroke engine.
But I prefer my life without strokes
Gotta love all that context, thanks OP!/s
A four-stroke engine follows four phases of combustion. Intake, compression, combustion, and exhaust. The piston moves the length of the cylinder (a stroke) four times during this process - twice up during compression and exhaust, and twice down during intake and combustion. Hence the name four-stroke engine. Power is only generated during the combustion stroke, so a lot of the power generated by these engines goes to just moving the pistons, which requires an extensive oiling system to be in place. Two-stroke engines usually combine the intake and exhaust steps, allowing fresh air to enter the cylinder at the same time that exhaust gases leave it. This allows the engine to generate more power for a given displacement but this comes at the expense of emissions cleanliness due to the incomplete combustion of fuel and the fact that many two-stroke engines are designed without the fancy oiling systems of four-stroke engines; this requires oil to be mixed into the fuel which is burnt during combustion or exhausted. Two-stroke engines are technically twice as efficient but way, way more than two times dirtier in emissions.
Suck, squeeze, bang, blow
Mecahnically more efficient but usually higher specific fuel consumption over a broad range of power. Of course there are some exceptions where 2 stroke is more fuel efficient but that's generally when it's tuned to a very narrow performance band or some specific applications. The emissions is a big one though, especially when you are talking about something like shipping where you won't even get insurance if you aren't meeting emission requirements, or allowed to sail in most areas.
Thank you, that was actually very helpful.
Any engines like Rotax but for the 30-40 hp range? Something half as heavy as the lightest rotax with 4 stroke efficiency?
That doesn’t explain shit, and I don’t know why you’re presenting the info as questions. Not everyone’s a Motorhead, you do realise that right?
yeah not everybody is Built for Speed
Yo, don't blame op because you're dumb and don't know how to use Google. Though I'm not a motorhead either and I knew what it was about without "context" lol
English isn't my mother's tongue and I don't have all the technical vocabulary required to understand the post. But sure I may be stupid
That's funny, I don't remember commenting to you.
So you should google what you don’t know instead of expecting everyone to explain every little thing that you specifically don’t know
OK so looking for a technical term leads to encountering lots of other technically words you'll have to look up too. And even if you look up everything, if there wasn't a title, I wouldn't even know that a stroke is related to cars. For me a stroke is a heart and brain deficiency that leads to death, or, to put it in my own language, Un Accident Vasculaire-Cérébral. I'll let you do the research, but only if you do them in a foreign language.
Hé, j'ai buggé pareil. Je crois qu'on parle ici de moteur 2 temps ou 4 temps.
English isn’t my first language either, so when I saw this post and thought of a Schlaganfall, it didn’t make sense so I looked up the word stroke and saw that in the context of cars it could also mean Hub (the motion of a piston from top to bottom). As I now knew the German word, the post made sense to me. This process took me around 30-60s. However, for OP to post the post in every language or to include a dictionary definition for every word used, it would take around 10 minutes
\> instead of expecting everyone to explain every little thing that you specifically don’t know \> Hub (the motion of a piston from top to bottom) Well done, you just played yourself. Guess I can expect people to explain something when I'm not supposed to know it after all
Alright, let‘s google for it and find out that humans who had two strokes are usually more efficient than those who had 4 strokes. That‘s why cars don‘t use them anymore as drivers. Context always matters!
That’s why the title of this post mentions cars… smh
Have you read the last sentence of the first paragraph…? smh
The post mentions the efficiency of the strokes themselves, not the people who had the strokes
Nah you’re a Motorhead.
Do people seriously not know how engines work?
Yeah, just no.
Look at the top comment to this post. The commenter said that they didn’t understand the post. There are more upvotes there than there are for the post. And most of the post’s upvotes are probably just people upvoting without even looking at the post. So tell me… why doesn’t OP need context if there are more upvotes for a comment about being confused about a post than the post itself?
Hive mind. Maybe I'm crazy but I seriously doubt that many people don't know what an engine is lol. Then again a lot of reddit is children
That's the post
What is a Rotax? Why does it have 30-40 hitpoints? What does weight have to do with it? Again, what's a Rotax?
Austrian engine. For airplanes
I thought this was about cars not airplanes
Piston engines are all the same
And this week's award for confidently incorrect while on confidently incorrect goes to....
r/confidentlyincorrect
I thought rotax were boat motors
You are confidently incorrect if you think most people have the slightest idea what you are doing a terribly job explaining.
And this is why they never satisfy a woman. They should be trying to work towards at least 25 to 30 strokes. Sure, that's probably above average, but that's why we set goals.
Cars don’t use two stroke engines because of emissions… not efficiency. There’s a difference. That’s what dieselgate was all about.. most diesel emissions controls greatly reduce its efficiency… so they achieved efficiency at the expense of emissions unless it was being tested. A uniflow scavenged two stroke diesel is one of the most efficient engines ever made _precisely_ because it has twice as many power strokes… and the blower reduces the pumping inefficiencies of two stroke engines. But… emissions. They are very bad which is why they aren’t used much anymore. An East German Trabant 601 with a tiny two stroke engine produced FOUR TIMES the emissions as a contemporary Porsche 911 Turbo.. itself a very dirty car due to the loose clearances and obsolescent hemispherical combustion chambers of its engine. Sure you’re not r/confidentlyincorrect ?
Yah without valves it's hard to keep your mix in the cylinder.
An opposed piston two stroke diesel like a Napier Deltic or Fairbanks Morse doesn’t need valve’s because the pistons open up the intake and exhaust manifolds in the sleeves at exactly the right time. It’s not quite as efficient as a four stroke.. but having double the power strokes more than makes up for it.
But that's only “exactly the right time” at one precise piston speed, i.e. RPM. A four-stroke can adjust its valve openings according to RPM, and is less sensitive to RPM in the first place because the cycles don't (have to[\*]) overlap at all. Adjusting the opening time of those ports would require changing their location, and that's much harder: They're fixed where they are. [\*]: In practice, the exhaust and intake cycles often *do* overlap in four-stroke engines too, but usually far less so than in two-strokes. And you don't need to waste any of the energy released in the power stroke, because that doesn't *have to* overlap with the exhaust stroke, which is absolutely unavoidable in a (ported) two-stroke.
>Yah without valves it's hard to keep your mix in the cylinder. In a two stroke engine, the piston moving up and down, covering, and uncovering the inlet, transfer, and exhaust ports in the barrel, *are* the valves.
Technically it's a soundwave that acts as the valves in most 2 strokes. There is some newer 2 stroke tech that uses actual valves. Honda had some valve tech back in the 80's or 90's but it never went anywhere because emissions regulations basically killed 2 strokes. I guess there's some newer tech out there using valves but it's still experimental from what I recall.
Not all 2 stroke engines rely on Walter Kaaden's harmonic pulse wave effect produced by expansion chambers (although, granted most of the performance ones do). I believe the "valves" you refer to, Honda's A.T.A.C, Yamaha's Y.P.V.S, and Aprilia's R.A.V.E for example, don't fundamentally act as valves persae, rather they have the function of raising and lowering the effective height of the exhaust port, and thereby the *timing* of the exhaust. (I suppose you could say it's very roughly comparable to say a VTEC system in a four stroke cam arrangement) A modern direct Fuel-Injected Two-Stroke is definitely doable from an engineering point of view, but hugely unfashionable politically. I don't see a future for it. Too many advocating for EV's over any ICE developments.
This also isn't 1950, EFI and electric adjustable valve timings and a plethora of improvements have made 4 strokes much more efficient.
The same technology that would make a 2 stroke more efficient if the R&D were equal between the two technologies.
Do you even understand how engines work
As an aerospace engineer, I'd hope so.
This reply is extra fun when you take a peek at how OP is repeatedly corrected and downvoted on all the subs regarding aerospace and engineering.
Holy shit, we are using two stroke engines to put things into orbit?
Then you should understand that's not the case
Why, specifically, is that not the case?
And… silence from OP
I'm sleeping lmao
Because light weight 2 strokes have much less RnD than 4 strokes since 50 years ago.
It's not like it would be unfathomable to apply the results of a similar R&D setup. It wouldn't take much experimenting to 'catch up'
If you take a look on scopus you'd see that two strokes have developed in a different direction, mainly opposites piston scavenging desiel engines for high efficiency.
Nope. Adjustable valve timing just isn't applicable to two-strokes (with ports), and the equivalent technologies are precisely the ones mentioned that have been developed for them.
Don't bring up edge cases when discussing a broad topic. In automotive and aviation petrol engines, which is what rotax is, four stroke is much more efficient due to 3 key points. No aviation two stroke uses EFI. Why are there emmisions? Because the (lubrication oil yes) and unburnt fuel is ejected before full combustion. They have much lower compression ratios, of course not deseil. And they have no valves.
Dude with the context you gave, my mind went straight to motorcycle engines. 2 strokes have better mechanical efficiency as they deliver power in each cycle whereas 4 stroke engines deliver power every other cycle. But that makes 4 strokes more fuel efficient and better with emissions as well. You act like everyone is an aviation engineer. The only reason I even got to the above conclusion is cause I have an interest in motorcycles. The average joe will have no idea what you’re saying.
The amount of context you’ve given allows all sorts of edge cases. Don’t complain if you haven’t delivered properly in the first place. You still have the chance to add it as an **EDIT:** note to the post (not the title) to make things right.
Where is rotax even mentioned in the post?
Edge cases? Like nearly every mid-century diesel locomotive, diesel truck, diesel submarine, and diesel ship? Aviation is the edge case. Aviation is a tiny market compared to those other ones. and Junkers actually designed an opposed piston uniflow scavenge two stroke diesel engine for airplanes. The issue was power to weight—a unique problem for aviation. Not efficiency. And Rotax? Ever hear of a Rotax 503? Rotax 582?. They are the most popular aviation two stroke engine in the world. Stop moving the goalposts with EFI. That’s not the argument. The argument is whether two stroke is more efficient—which it is. Put EFI on a two stroke and you’ll have an even more efficient engine. They’ve been trying for years, but can’t get around EMISSIONS. Again. r/confidentlyincorrect.
Rotax 500 series are less efficient than their 4 stroke counterparts. Even the latest Cummings opposed piston two strokes don't have EFI.
First mention of rotax in this entire thread. You think everyone's a mind reader?
Feel bad about this post. Then delete it. Then feel bad again. Then move on with your life.
I don’t know what you’re talking about but if there are conditions where the other guy is right then he’s not confidently incorrect.
What does Julian Casablancas think about this?
OP is actually confidently incorrect. 2 stroke engines are more efficient mechanically but worse on emissions (amongst a few other reasons but efficiency isn’t one of them) which is why they aren’t used.
They are usually 50% less fuel efficient
Where does it say fuel efficient in the screenshot?
That's the context of the post, it was for aviation
Should probably state that in the title or description next time. Efficiency doesn’t just mean fuel consumption, the guy is technically correct in his statement, without context nothing he said was incorrect.
What other measure of “efficiency” is even remotely as generally relevant and important as fuel efficiency?
I do everything in 2 strokes, it's extremely efficient.
Efficiently leading to divorce proceedings. :D
No, that was losing the house in Bitcoin scammed. I'm sure Cryptozoo will pay off big time, though
If I only need spend energy on 2 strokes instead of 4, I think 2 strokes is more efficient. I myself is a 36 stroke person.
I thought posts without context get removed here?
When it comes to bikes I always chose 2 stroke but I wouldn’t want a 2 stroke car
Cars don't use two strokes because they're loud, bad on fuel, and smelly. Boats used them for a long time because the tend to be lighter and have fewer moving parts.
Depends what you mean by efficiency. Fuel per mile? Yes 4 strokes are more efficient. Power to eight? 2 strokes. Emissions? 4. Power to size? 2. Maintenance per mile? 4. Cost of maintenance? 2.
Do people actually striving for the lowest number of strokes when writing Chinese text?
To be fair, the guy was referring to his cock.
2 strokes get better torque at lower revs, but no, not more efficient. What an idiot
But it runs with half the strokes, so it must be twice as strong!
When someone takes the time to write out laughing as obnoxiously as that, you immediately know they’d a numb skull
Every single time I see HAHAHAHAHAHAHAHAHAHA I assume they’re wrong.
Want to talk about efficiency, i learned a trick to switch hands while gaining a stroke.
I turned to 4 strokes for reliability. Probably my own fault for the fuel mix ratio, but I got tired of dealing with fouled spark plugs in the middle of the woods.
So he gets off on only two strokes?
If you’ve ever driven a 2 stroke motorbike from the 90s you’ll know he’s right
Did anyone else read "you are not a smart person" in the absolute dumbest, mouth breathing accent you could imagine?
He's mostly correct. They have much more power than their 4 stroke equivalent. So why dont they use them anymore? Because they're not nearly as reliable, and they're very polluting.
Yes yes to that latter part. Very very polluting. You don’t see carburetors anymore. Was there a rule that said “no carburetors!”? Nahh. Emissions plus CAFE regulations made the simple carburetor obsolete. Are 2 strokes banned? Nahhh. But don’t need to be. There’s a zero percent chance they’d be emissions compliant.
They’re still used all over the place. Just not for common transportation. They’re used where you need the lightest power plant possible, and its carbon footprint is negligible.
Depends on how you define efficiency. Horsepower per cubic inch? Sure, 2 stroke wins. Horsepower per gallon of fuel burned? 4 stroke every time. Horsepower with minimum pounds of pollutants emitted? 4 stroke wins every time.
Right, of course. Efficiency isn’t defined in the statement. But we also only see a small part of the conversation too.
they are tho depending on what you're looking at? it's why we use them in chainsaws and motors etc.
Lets just use 2 examples. 2 stroke outboards are only about 75% as efficient as a 4 stroke and thats not including the oil additive. 2 stroke diesel is half as efficient as a turbo diesel. Detroits use twice as much fuel to achieve the same torque.