2 stroke technology as compared to 4 stroke

[RamsesRibb]

Everyone has their favorites for one reason or another but I hear all the time about the superiority of the modern 4stroke 450 class over the old 250 2stroke engines. I myself find this comparison completely annoying. For one thing the comparison is like pitting a weed eater against a lawn mower. The displacement is nearly double and the power output nearly equal.?. Sure it has tractability but that's not the point. The 4stroke 450's where basically one cylinder shaved off of a massively researched and engineered Formula 1 engine. With the same amount of research and development things would be different. And displacement being equal there is no contest. Why not put 450 2 stroke engines in the 450 class? Would that then flatten all the hype? I'll bet the 2 stroke is overall lighter as well as outputs more power.

The following is reference information:
Michael Harrison from the DeepScience BIGENZ team has this to say:
Most of what is written on advantages and disadvantages of 2 strokes Vs 4 strokes is not actually correct.

Take for example the lubrication issue of 2 stroke engines, sure small chainsaw engines may have the oil mixed with the fuel but this is not a direct result of the engine being a 2 stroke, this is just a result of someone designing a very simple engine. look at any large Caterpillar, or Detroit 2 stroke they have conventional oil sumps, oil pumps and full pressure fed lubrication systems and they are 2 stroke!

Also, the argument about valves of 4 strokes versus the reeds and ports of 2 strokes is also incorrect. Sure some simple 2 strokes may use very primative systems to achieve the conrol of fuel/air mixture into the engine and exhaust out of the engine but again this is not a function of them being 2 stroke! I've worked on 2 stroke engines that feature poppet valves in the head (like a standard 4 stroke) - but they are definately 2 stroke - it's just that engines like this are not so much in the public eye - next time an ocean liner (ship) pulls into port check out its 2 stroke, turbo charged, direct injected diesel engine!

Finally, the arguments of simplicity, weight, power to weight, and cost of manufacturing are not a function as such of 2 stroke versus 4 stroke engines. The mistake of most of these commentaries is that they are comparing a simple chainsaw 2 stroke engine with a complex 4 stroke engine from a automobile - not a very fair comparision.

As far as the exhaust emmisions of 2 strokes - check out the Surrich/Orbital 2 stroke design that Mercury outboards are using - this is as clean burning as any 4 stroke.

The ONLY correct comparison of 2 strokes with 4 strokes is that a 2 stroke can (in theory) produce twice the power of a 4 stroke for the same sized engine and the same revs.

[christph]

Hear, hear. Like many people I like both 2 and 4 stroke engines--but right now I happen to be on a 2 stroke kick. I think California and the EPA are the primary reasons 2 strokes were replaced with 4 strokes; their emissions aren't as good. KTM still sells and develops 2 strokes. Their 250SX motocross bike has an all new engine this year. I also read that their 2 strokes are their best sellers in Europe. Yamaha still makes 2 stroke motocross bikes but they are less committed than KTM. One benefit you forgot to mention is that 2 strokes are much cheaper and easier to maintain. In motocross circles I've heard people complain that 4 strokes have made the sport too expensive. I wouldn't be surprised if 2 strokes made a come back in the future. I think Honda and KTM are working on fuel injection. The biggest hurdle, I think, is emissions and the relatively weak economy. I hope another golden era of quads is just around the corner. I've always thought that the manufacturer that came out with a 3 wheeler would make a killing. Perhaps Yamaha will. Honda has gotten too conservative.

[Herboso]

They tried to kill the 2 stroke but I think it is making a come back. There is money to be made in keeping it alive too. I think though that it won't be the simple 2 stroke engine that we have come to know. Emissions is definitely the problem. Not just off road vehicles but also for outboard motors. Ever been out on a lake on an early morning fishing trip and see the thick haze floating over the surface from the trolling motors? I'm not an environmentalists but got to admit its kinda detracting to see that. I guarantee engineers are at work redesigning the 2 stroke to be cleaner and yet not lose the advantages of weight and simplicity. It presents an interesting engineering problem. I think the manufacturers first reaction to increased restrictions was to drift away from 2 strokes and put more effort into refining the 4 stroke and getting more performance out of it. It seems there is an effort now to go back and refine the 2 stroke. These are just my impressions. Will be interesting to see.

[John Tice]

YOU are Rite on; I was in the submarine service for a couple of years; Our power plants were 2 Fairbanks opposed 10 cylinder 2 stroke engines. I believe the same power plants which are in today’s railroad engines. Every time a train rolls by I reminisce about the boat USS Pickerel SS524.
This write-up needs to be forwarded to as many places as possible. 2 strokes twice the power as a comparable displacement 4 stroke. Commen sense for Dummies. It all boils down to $$

John Tice
503-593-2908 Alternate 541-508-3944
www.smallenginemachineworks.com & www.nwsleeve.com
Turning Custom Cylinder Sleeves Since 1971

[Herboso]

Just read this interesting article. Clearly there is a lot of potential for this technology.

http://www.cycleworld.com/2014/02/07...e-streetbikes/

[86T3]

4 strokes are easier to ride, plain and simple, that's why they are taking over. My Tecate 500 is faster in a drag than my 450 but I'm twice as fast on the 450 on anyour other race. 500cc 2 strokes are more like a 4 stroke with their broad power band, but they are still harder to ride. The tourque on the 450s is insane from idle on up, youre never in the wrong gear with one.

I'm sure the emissions helped start the change though, I won't doubt you there. But, 2 strokes can be made to run clean, look at the new 2 stroke outboard motors. They barely use any oil and don't make much smoke.

As for the lubrication, 2 stroke diesels are completely different than 2 stroke gas engines. They have regular valves and are obviously fuel injected, but they need a blower to force air in the cylinder because they can't make vaccum. They also are very inefficient. My bus has a non turbo 8v93 (that's 744 cubic inches) and it's only 400 hp. I go up hills at 17mph and get 4.5 - 6 mpg depending on it I want to do 68mph on a highway or 62. A modern 4 strokes diesel will cruise at 70 and get 10 mpg.

I own 2 strokes and enjoy them greatly, they are more fun to ride, but when I go out a race I bring the 450.

[RamsesRibb]

4 strokes are easier to ride, plain and simple, that's why they are taking over. My Tecate 500 is faster in a drag than my 450 but I'm twice as fast on the 450 on anyour other race. 500cc 2 strokes are more like a 4 stroke with their broad power band, but they are still harder to ride. The tourque on the 450s is insane from idle on up, youre never in the wrong gear with one.

I'm sure the emissions helped start the change though, I won't doubt you there. But, 2 strokes can be made to run clean, look at the new 2 stroke outboard motors. They barely use any oil and don't make much smoke.

As for the lubrication, 2 stroke diesels are completely different than 2 stroke gas engines. They have regular valves and are obviously fuel injected, but they need a blower to force air in the cylinder because they can't make vaccum. They also are very inefficient. My bus has a non turbo 8v93 (that's 744 cubic inches) and it's only 400 hp. I go up hills at 17mph and get 4.5 - 6 mpg depending on it I want to do 68mph on a highway or 62. A modern 4 strokes diesel will cruise at 70 and get 10 mpg.

I own 2 strokes and enjoy them greatly, they are more fun to ride, but when I go out a race I bring the 450.

Well your examples prove the point of my post. You are comparing old technology 2 stroke to new tech 4 stroke. Not even considering the chassis that they are built on. Same with the diesel. You are comparing modern turbo diesel 4 stroke to 1950s tech 2 stroke.

The EPA is not even constitutionally allowed to dictate what citizens may bring to market and use. They are supposed to have power only over commercial operations. We the people really need to start taking the authority away from these people.

[86T3]

It's not the chassis that makes my 450 better, but I can agree that the 500 is old tech and so is the Detroit. I do think that 4 strokes are more efficient though, and that's why 2 strokes have been abandoned.

[christph]

The Constitution--what's that? We're now governed by army of un-elected bureaucrats whose sole job it is to make regulations. Personnel is policy. Just look at the EPA. It used to be that they only regulated navigable waters. Now they want to regulate puddles that form in your backyard when it rains.

[yaegerb]

Love the title. Bring on the discussion, because I often wonder where do we draw the line between what's better 4 vs 2....

I have taken it upon myself for the better part of 3 years to understand the workings of the 2 stroke power plant and one conclusion I have drawn is it's anything but simple. Rather, in my humble opinion it's a very complex system where math is your friend, port timing is king and squish velocity can be your antithesis among many other factors that will downright kill your beloved 2 poke friend.

I have also learned they are anything but efficient. The mere fact that a expansion chambers first purpose is to ensure adequate cylinder stuffing should give you a clue that power lost through your exhaust ports in the hope to regain on the next up stroke. However, like 86t3 suggested, the newer marine 2 strokes are light years more efficient than its earlier cousins. The only reason I know this is we have two fishing boats, one with a fully overhauled 1987 Johnson 25 hp motor and a newer Lowe boat with the E-tec G2. You can mix them with the same oil to fuel ratio and the Johnson will smoke like a freight train and still soot (not foul) up the plugs. The e-tec has run all summer and the plugs look like they had been sitting in a four stroke power plant. One thing is for certain, The newer 2 stroke definitely have cleaned up their act....but I digressed only to make a point. How far could two stroke ATV technology have come if they kept improving their power plant.

86t3 is correct on another front. 4 strokes (450 is the argument here), are just easier to ride, argument over....ask any racer with a few years seat time on either machine. Their torque is massive and their rideability is unquestioned. I have raced and trailed both and I can tell you the 450 is like riding a couch. In today's world, everyone wants what's easier, and that sucker IS easy to ride. I also might add that it's predictable power (no RPM hits to really speak of) and that power is easily obtained in any gear. Thus, a plus for the weekend warrior.

Man, this sounds like I am for 4 pokes...lol

I love both, but my heart is with the 2 stroke. There's nothing like the hit of the 2 stroke and trying to stay on the throttle while carving a bowl or taking that blue line to try and pass the guy in front of you. It's just in my genes I guess. Also I would add that they are a cheaper power plant to work on by far, but again, don't think that implies simplicity. Imagine where the 2 stroke would be today if the Yamaha engineer (his name escapes me right now) had spent 5 years developing a two stroke power plant instead of the 4 for the YFZ 450.

Oh, and I heard some rather interesting news a few months ago from my buddy at my local stealership. Apparently Honda is doing some r&d on a new 2 stroke power plant. For what use I have no idea. May be another false lead...but what if it isn't

[arlaunch]

A good Kevin C. article .

http://www.cycleworld.com/2015/08/20...-kevin-cameron

[El Camexican]

Ring-a-ding ding is what makes my heart sing

[barnett468]

...squish velocity...

4 strokes also have an optimal squish/quench clearance on closed chamber heads that reduces the potential for detonation.

I have also learned they are anything but efficient. The mere fact that a expansion chambers first purpose is to ensure adequate cylinder stuffing should give you a clue that power lost through your exhaust ports in the hope to regain on the next up stroke.

The exhaust on a 4 stroke is also designed to increase cylinder filling through a process called "scavenging" . If you remove the exhaust from your bike or car etc, it will run like crap.

The intake system on a 4 stroke is also designed to work as a complete system on a 4 stroke . If you Google "Tuned port intake" you will find some info on the subject.



PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR

[towboater]

EMD 2 stroke engines are still going strong today,but they have put alot of research in the development of injectors and piston ,liners and exhaust to meet epa emmissions,but this is a hole defferant breed of 2 stroke engines.

[Gearheadtom]

Look at modern snowmobile engines. 2 strokes have come a long way, long gone are the days of the piston ported slobbery gas spitting engines.
They're really not any harder on gas than a 4 stroke, and the emissions aren't much worse. Fuel injection directly into the transfer ports, electronic power valves, and electronic oil pumps. Only hard parts seems to be keeping any 800 from grenading evey 5000 miles.

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