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/ask-kevin-why-no-modern-two-stroke-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/two-strokes-in-motogp-racing-will-they-ever-return-by-kevin-cameron

[El Camexican]

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

[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.

Sent from my SM-G903W using Tapatalk

[RamsesRibb]

A good Kevin C. article .

http://www.cycleworld.com/2015/08/20/two-strokes-in-motogp-racing-will-they-ever-return-by-kevin-cameron

That guys sounds like a wimp. That 200hp 500 seems like the perfect engine for my Trisport. [emoji12]

[RamsesRibb]

I think this is what someone was referring to about Honda's plans.

http://newatlas.com/honda-two-stroke-with-fuel-injection-patent-filing/38529/?amp=true

[RIDE-RED 250r]

Rotax has been leading the way on 2-stroke advancement and compliance with the more stringent EPA standards with their ETEC 600 and now 850 2-stroke sled engines. Technology they inherited when they bought out OMC who was the umbrella under which Johnson and Evinrude outboards were manufactured. The outboard DI system was a bit different from what I have read, but it wasn't too difficult for Rotax to adapt that system and implement it on their sled mills. ETEC came out in '07 if I recall... at the time of introduction the 600 was claimed to be capable of close to 20mpg and the 800 16mpg under normal riding conditions. Obviously that number can change with riding habits and conditions... I haven't been into sleds and following things in that area for a few years now, they may have improved since then.

The tech is there, the industry is against it, not sure why. Some have hypothesized that the big manufacturers (Honda being the primary offender) are so invested in 4-stroke that they used their influence on the racing circuit to put the final nail in the coffin of the 2-stroke mill. They simply do not want to market 2-stroke engines any more... As I said, I have seen it hypothesized in that way, not sure if I go along or not..don't really care though as my wing-dingers are still in my garage with no plans of replacing with anything "new".

I don't race, but I have ridden all of the major 450's except the Kawi. 86t3 is right, torque all over the place and I can see why they are the choice of so many racers. It makes sense to me.

[cr480r]

All the efficiency and rideability in the world will never make me enjoy 4-stroke sounds... I ride purely for enjoyment. I find the typical 2 -stroke power build very exciting .. I really enjoy the sounds and smells... And I enjoy working on them. They are powerful light, simple, affordable, and reliable... That's all I need

[atc300r]

Honda built a two stroke years ago to meet smog requirments I think it was $650,000 Cr 250 prototype.

[Herboso]

How much do you think California's strict OHV registration program influenced the issue?

[RubberSalt]

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.

Sent from my SM-G903W using Tapatalk

Gearheadtom is right. The sled community has been pushing the envelope of the 2 strokes. Not only with emissions, but all sorts of new technology to help with emissions. The 800s crapping out after 5k is pretty good if you ask me. They are pushed hard, just like the 450s. Expect service life to crap out fast!

Heres an example of the power produced my modern 2 strokes. These are set up to operate in a narrower powerband to take effect of the CVT, but none the less.
2016: Rotax 800r e-tec - 165HP. Thats 82.5HP per 400cc cylinder
2016 Artic Cat XF 6000 - 600cc, 125hp, 62.5hp per 300cc. This is a tame engine. Made to last.
2016 Ski-Doo x with T3 package, 147+hp. 73.5hp per 400cc.
2017 Ski-doo 850 e-tec, 170HP, 85 per 425cc.

These are lean settings used to meet the EPA requirements. Many aftermarket set ups push the 800ccs well into the 180-190hp range. Little.. ridiculous!

These are all fuel injected. They have oil systems that use next to no oil. No more mixing, and i don't mean oil is injected into the gasoline. The oil, is closer to the method used on a automobile. It's pressurized and sprayed directly onto bearings and the places that need it. most cars leak more oil than these use in a season!
Modern sleds have adjustable compression. Yes, compression. As you drive higher in altitude, your compression drops due to lack of air density. To compensate for this, manufactures have begun including adjustable domes. With the turn of a wrench, compression can be increased. Offset jugs are showing up more often these days. Shifting the center line of the jug towards the exhaust a few mm makes a big difference in how much power is transmitted to the piston, opposed to the friction and the cylinder wall.

Any 2 stroke can be tamed the same way a 4 is, heavy flywheels. They help distribute the torque more evenly throughout the revolution of the crank. They rev up slower, but maintain the inertia generated by the piston during the combustion process. A pipe designed for a wider powerband also helps. It drops the amount of power, but broadens the torque. The majority of usable power(with gasoline!!) extracted in both 2 and 4 strokes is in the first 10-20 degrees atdc. The combustion process is complete by 25 degrees atdc. After that, it's mostly rotational momentum carrying the engine to the next power stroke.

[christph]

How much do you think California's strict OHV registration program influenced the issue?

Yes, unfortunately California's regulations significantly influence manufacturers because they are the biggest market in the country.

[oldskool83]

Ride both and see which one does everything and then some. Then come back and see if you feel the same about your argument. today 4 strokes are nothing like lets say 30 year old 4 strokes...they remind me of one thing, a sport bike 4 stroke and to that i am fine with everything they do.

I have one 2 stroke left....why, not sure I guess I thought it would be cool to have something old yet.

[Hurley250R]

Blow one up and see how much you love it then. Two strokes about $300 repair while a 4 stroke is $1200+

[oldskool83]

I have no issue with spending the money to build one. blow up a 2 stroke bottom end and top end and you are well over $300. Replate alone is $140 at most placed, plus all your bearings this and that. It's not that simple. I've rebuild 2's and 4's and not had that issues of spending money on a 100% fresh motor, not a new piston and call it a day. In today's day and age good maintenance and not revving the piss out of stuff really goes a lone way.

Maybe i have not learned anything in 27 years of riding about everything.

[RIDE-RED 250r]

It's a fact that the "modern" 4-strokes, mainly the performance oriented 450s are very high strung mills and will not enjoy the service life of your older school thumpers. With anything you build or design, when you push for higher and higher power and RPM potential in a given displacement, you WILL suffer loss of service life and accelerated wear of the major engine internals. This is true of anything from chainsaws to wheelers, to boats, to supercharged BBC's set up for drag racing and making 800hp.

Now I would tend to agree with you oldskool83 that most 450 major components are priced about the same as the old 2-strokes... But where costs with overhauling a 450 can and do climb well past the cost of overhauling a wing-dinger is when you start talking cams and heads. And they do go bad and/or get damaged to the point they need replacement when someone pops one at times. And I agree, good maintenance and not abusing the engine will get you farther down the trail/track.

I remain impressed with how they have designed these modern thumpers to run. I have owned a couple of Z400s in recent years. Liked how they ran, had some trouble with one I couldn't figure out... Did a fresh piston and crank with crank bearings thinking it would cure it and it didn't. Sent them both packing in favor of a 350x and 400ex. Nice quads, run strong, but HATE dual cams and messing with shims to adjust valve lash!

[RubberSalt]

Oldskool is right not overrevving and maintenance will keep both engines going for a long time. Below is some ball part ideas of what it takes in the case of catastrophe and the difference when maintaining the engine. I've decided to compare a trx250r and the yfz450r. The labor cost are from local sources in wichita ks. The key is proper maintenance and not running the engines into the ground... Expect the below the general maintenance about ~100 hours on both machines. You can expect to wear a crank out on a 2 stroke a lot sooner than a 4 stroke. Higher oil ratios augment this greatly, but it's inevitable. Its the trade for the extra HP.

2 stroke typical 250R
Worn top end on iron sleeve=$130 for piston. $40 for a bore.

Worn top end on plated top end, $130 for piston and $140 for replate
Trash a crank.. $75 bearings seals and gaskets, $120 for rod, $90 for labor

Worst case, trashing the bore and crank: $565

General maintenance:
Piston:$130
Gaskets:$25
$155 total


4 stroke -based of the yzf450r
Worn top end on iron sleeve=$150 piston and $40 bore.
Worn top end on coated top end, $150 for piston and $140 for replate

A bad 4 stroke day
Float a valve - $90 per valve<- they are using titanium in the high performance machines these days.
Piston $150
valve guide $150 for Labor+parts
seat $40 for repair +parts
Gaskets $40
$470


Oil pump locks up or oil starvation due to plugged filter
Piston $150
Replate $140
Cam $200
Rod $150+$90 labor
valves(probably fine)
Gaskets $40
$770


Top end wear and tear due to lack of maintenance: 5 valves. $450 + 5 seats @ $40 each
Piston: $150
Timing chain being stretched $20
Worn chain guides: $60
Gaskets $40
$930

Top end general maintenance - assuming all other is maintained properly.
Timing chain: $20
Piston: $150
Gaskets: $40
$210


Grenade a cast piston from over revving for to long. Oh god lets not go there.


Didn't even want to get into covering the transmission causing potential problems on the 450s. or a timing chain that jumps and smashes valves

[RubberSalt]

http://www.3wheelerworld.com/showthread.php/104439-What-does-a-450r-rebuild-cost throwing this out there.

[86T3]

Maintenence is more expensive on the new 450s, that is true for sure. I got a ridiculous deal on a full mx ready 08 yfz this year with a motor in a box. I bought it because I have a rebuilt yfz motor that has been stolen from me along with the rest of the quad, and I hoped that I would be getting it back this summer. I haven't gotten it back yet, it's a whole other story, so I took the mx motor in to my shop to get it checked out. It came with a new piston and top end gasket kit, I was hoping it could just be put back together and I'd be good to go. Well, it was a race motor and even though it didn't blow up it needs practically everything. The timing gear on the crank was getting wore into or something so it needs a new crank. Needs a ton of bearings, all the valves are out of spec, it came out to around $1500 in parts and like 250 for labor. I picked it up and payed for disassembly, I couldn't swallow that bill. And thats not including the price for a new piston because I had one! They said a yfz came in last month that needed a a rebuild and a new head, that guy ended up doing the same thing I did. I still think the 450s last longer than 2 strokes though, there are examples of each motor that have been together for many years with good maintenence and still run good. But I would like to know where you guys are getting cylinders replated for 140, that's a really good deal

[RIDE-RED 250r]

Still haven't got your quad back eh Joe?? That sucks! Here's still holding out hope for ya... BTW, good post...other than the stolen quad part...

[yaegerb]

Maintenence is more expensive on the new 450s, that is true for sure. I got a ridiculous deal on a full mx ready 08 yfz this year with a motor in a box. I bought it because I have a rebuilt yfz motor that has been stolen from me along with the rest of the quad, and I hoped that I would be getting it back this summer. I haven't gotten it back yet, it's a whole other story, so I took the mx motor in to my shop to get it checked out. It came with a new piston and top end gasket kit, I was hoping it could just be put back together and I'd be good to go. Well, it was a race motor and even though it didn't blow up it needs practically everything. The timing gear on the crank was getting wore into or something so it needs a new crank. Needs a ton of bearings, all the valves are out of spec, it came out to around $1500 in parts and like 250 for labor. I picked it up and payed for disassembly, I couldn't swallow that bill. And thats not including the price for a new piston because I had one! They said a yfz came in last month that needed a a rebuild and a new head, that guy ended up doing the same thing I did. I still think the 450s last longer than 2 strokes though, there are examples of each motor that have been together for many years with good maintenence and still run good. But I would like to know where you guys are getting cylinders replated for 140, that's a really good deal

Agreed, that is a CHEAP nikasil price.....spill the beans guys

[oldskool83]

Agreed, that is a CHEAP nikasil price.....spill the beans guys

powerseal in PA and eric gorr racing. just email or go to their web sites. eric gorr did my last motor and it was about 140 for welding rebore and replate.

[yaegerb]

powerseal in PA and eric gorr racing. just email or go to their web sites. eric gorr did my last motor and it was about 140 for welding rebore and replate.

Wow, that's competitive pricing. Is that nikisil on any size bore or is it more for bigger bores?

[86T3]

You must be better friends with him than I am, it says $180 for 50-150cc and $250 for 175cc and up on his site. I still think 250 is a reasonable price though, and he does quality work

[86T3]

Power seal is $184 for a replate. http://www.powersealusa.com/prices/

[oldskool83]

I had other work done so maybe that's why I got it cheaper not sure. All the dealers around me use power seal but I like EGR due to him being able to port and redone the heads also in 1 place, kinda nice he was factory yamahas engine builder thru the good years too.

[JesseA420]

great thread.

21st century 2 stroke technology is easily obtainable now on our 30 yr old bikes thanks to cp cylinders and the amount of knowledgeable builders specializing in 250r and banshee based motors today. to the folks that prefer 4 strokes with the argument "they simply can do everything, compared to 2 stroke" has never rode a properly setup 70+ hp 250 based bike with a broad power curve. along with the power to weight ratio and the power per displacement ratios, they are just as capable, just as reliable, and light years more fun. if you're not riding for the fun and the thrill, what are you riding for? for clarity this is excluding work purposes.

[RubberSalt]

Unfortunately, Jesse, It's not as simple as that. Forced oiling and fuel injections are a couple things we can't easily adapt to our old machines. When oil is being pumped through the crank, and into the bearings, that's something we can't easily adapt. Once you switch to this set up, you also can't switch to any off the shelf 2 stroke oil. Viscosity comes into play now.
Fuel pumps alone also require more power than most stators can put out.

Many of the cylinder's arn't offset either, but this can be corrected with the CP Cylinders.

I'd love to see direct injected 2 strokes. There's plenty of room in the dome. Think of how much the pollutants would drop then!. Next to nothing due to the oil injections, and incredible efficiency due to direct injected fuel. Gasoline would no longer be pulled into the pipe. Just air and exhaust gases.

We can reach the same power levels, but pollute a bunch more.

[JesseA420]

i obviously was talking about modern port tech, not direct injection.

[RubberSalt]

Even our port work hasn't changed drastically. We're a little more refined, but that about it. Our 125's hit a pinnacle in 98. KX250s were pushing 50+ hp from the factory in the mid 80s. The difference, is manufacture's are consistently producing the same power from machines. We've got better metals.

Powervalves originated in the 80s. Pipes made good power then. Pipes make better power today. Our head's have gotten better designs since the 80s, more refined today. Almost every aspect is better today, but not astronomically better than it was 30 years ago. We're not making much more HP, but more usable power now.

Lets take a look at the YZ125. The older information is more difficult to find. This should be fairly accurate though. It shows how we still use similar technology in one of the ever evolving engines introduced.

1974 - the OG, the YZ125 - air cooled Used a 7 port design
1977 - 56x50 bore x stroke - 32mm carburator
1980 - 33hp - air cooled
1981 - 33hp - liquid cooled
1982 - Power Valves added
1985 - 9 port design
1986 - 10 port design
1989 - plated cylinders - 9 port design
1990 - Stroke increased to 50.7mm
1994 - Stroke increased to 54.5mm, new powervalve design
1996 - 36mm tmx carburator - decreased crank case volume - redid the intake tract and air filter. - 7 port design
1998 - 34HP
1999 - 38mm tmx carburator
2000 - 30:1 oil mixture - Oldest manual I could locate.
2001 - 7 port design
2005 - Got a constant mesh gear box
2006 - 34HP
2013 - 30:1 oil mixture
2014 - 34.01 HP

The HP are claimed levels. The port designs are the number of ports. It doesn't reflect the shape, but you can search cylinders and see how they slowly evolved over the years.

[oldskool83]

Yep, reason next seasons bike for me is a fully built 1987 YZ250 vs a 2002-2004 because it's gonna do the same darn thing, just look cooler lol

[RIDE-RED 250r]

We certainly can greatly reduce emissions with different porting. Look up "stratified" porting for chainsaws. Along with Auto tune found on Husqvarna, and Mtronic on Stihls (both are electronically controlled carbs) these newer saws are more fuel efficient, and put out less emissions. These saws run faster and stronger to boot because the auto tune carbs keep them tuned for peak performance in terms of emissions which gives the side effect of peak running performance. They will adapt to any altitude, temperature, and pressure. Pretty cool stuff really. But i suppose that direct injection 2-strokes probably don't need strato porting as the fuel is introduced directly into the combustion chamber if I understand it correctly.

[El Camexican]

There must be a millions opinions on this subject, but along with them come a million variables as well. My thoughts (which may not be facts) are as follows.

Cost to Power Ratio

Power output plays a huge role in determining the life of an engine. Compare an XR400 to a SX450-F: One makes 30hp and the other makes 70+. Depending on the way either is ridden these next estimated numbers could vary a lot, but generally speaking one will run for hundreds if not a couple thousand hours on a few oil changes and the occasional valve and cam chain adjustment and the other has 15 hour oil change intervals, 50 hour (or less) valve adjustments and will need a piston and rings before the 200 hour mark as well as fancy valves, seats and many other parts soon after. And even if both engines were to wear out at the same time the cost of rebuilding the racer is much higher due to the exotic parts that are required to achieve the power levels it makes.

Now compare the air cooled 125cc two strokes still sold down here and used to deliver pizza with a 125 MX bike. Again, the racer makes more than double the power and wears out a lot faster due mainly to the RPM levels it’s used at and the MX bike will be needing a piston and rings well before 100 hours if run hard.

What doesn’t vary as much in the 4 stroke comparison is the cost of the engine rebuild between the two stroke examples. It’s just a piston, rings, wrist pin and 4 bearings every time. The cost of properly rebuilding race version of an “F” engine is outrageous. They’re also much more complicated and require tools and equipment that many of us don’t have.

As far as the rule of thumb about a 4 stroke needing double the displacement to match the power output of a 2 stroke I think that’s outdated info. A modern 250-F race bike makes more power than a 125 pinger and a 450-F race engine will tear the decals off a 250 two stroke as it wheelies past it. Reliability and cost be damned, modern race four strokes are impressive beasts.



If I weigh the benefits of either design as it applies to my riding situation it's like this...

My outdated KTM 300EXC 2 stroke makes about 50hp and 40 pounds of torque.
The sister four stroke of the day, the 450EXC made 42hp and 38 pounds of torque.


On the 300 I can get up to 150 hours on a set of rings and 300 on a piston. The crank and rod on my oldest engine has seen 3 pistons come and go over the last 7 years of use and is still good.
I see the 450’s smoking by 400 hours of moderate trail/endure riding and then they get sold off for $2,000 rather than rebuilt.

So a top end on my 300 engine costs me about $300 and 3 hours working at a leisurely pace while watching a hockey game and sipping on rum. If I needed to do the crank it would take a day and add another $300.
If I owned the 450 and wanted to do just a piston and rings the cost would be about the same, but I’m sure the time would go up and I may have to lay off the rum to make sure I don’t screw the timing up. Now if the valves and crank were spent things change a lot. Cost would be in the $1,500 to $2,000 range and I’d need to ship the head to the US. My riding time would be diminished as would my bank account, but the engine would likely last me another 400 hours and even more if I would do the rings somewhere around the 200 hour mark.

So up to this point the 2 stroke looks a lot cheaper and has a better bang for the buck, but there are other factors to consider. For example, the cost of the fuel & oil. The following is based on 100 hours of riding at an average speed of 20mph.

300
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/25mpg = 80gal. X $2.00 = $160
2 Stroke oil cost per gallon = $1.25 X 80gal. = $100
Transmission oil = $10 X once per 100 hours = $10
Total cost to ride for 100 hours is $270

450
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/30mpg = 67gal. X $2.00 = $134
Engine oil @ $7.00 per liter = 1.5 Liters X 20 hours = 7.5L X $7 = $52
Filter(s) $16 = 5 X $16 = $80
Total cost to ride for 100 hours is $266

So much for better fuel economy and not having to mix gas equating to lower four stroke operating costs. That fancy synthetic 4 stroke engine oil and frequent oil and filter changes the high power thumper needs eats it up.

Consider this as well:

You're stuck in a swamp and overheat and seize your engine. If it’s a four stroke you’d best start walking back up the trail to look for a quad to pull your broken bike out of the mud. If you have a 2 stroke you can just wait 15 minutes for the piston to cool off and kick it loose. Depending on how you ride you may not even notice a power loss and you could keep riding it until your next planned rebuild.

Now let’s say you’re a “ride till it breaks” guy. If you do that with a high powered 4 stroke the moment it “breaks” it will may take the head and cases with it, so your best bet is to part out what’s left on eBay when it happens. If you do this with a 2 stroke odds are the only additional cost to fix it that you’ll incur over a normal full rebuild when it “breaks” is to get the damaged cylinder plated, or sleeved.

Here are a few more comparisons:

The 300 starts first or second kick hot or cold. Kick starting a hot 4 stroke can lead to suicidal thoughts
The 300 weighs less that the 450
The weight of the 300 engine is situated much lower in the frame

So when I add up my two cents of opinion and calculations I think I’m better off spending them on a 2 stroke for how & where I ride and for my level of mechanical aptitude.

[Hurley250R]

There must be a millions opinions on this subject, but along with them come a million variables as well. My thoughts (which may not be facts) are as follows.

Cost to Power Ratio

Power output plays a huge role in determining the life of an engine. Compare an XR400 to a SX450-F: One makes 30hp and the other makes 70+. Depending on the way either is ridden these next estimated numbers could vary a lot, but generally speaking one will run for hundreds if not a couple thousand hours on a few oil changes and the occasional valve and cam chain adjustment and the other has 15 hour oil change intervals, 50 hour (or less) valve adjustments and will need a piston and rings before the 200 hour mark as well as fancy valves, seats and many other parts soon after. And even if both engines were to wear out at the same time the cost of rebuilding the racer is much higher due to the exotic parts that are required to achieve the power levels it makes.

Now compare the air cooled 125cc two strokes still sold down here and used to deliver pizza with a 125 MX bike. Again, the racer makes more than double the power and wears out a lot faster due mainly to the RPM levels it’s used at and the MX bike will be needing a piston and rings well before 100 hours if run hard.

What doesn’t vary as much in the 4 stroke comparison is the cost of the engine rebuild between the two stroke examples. It’s just a piston, rings, wrist pin and 4 bearings every time. The cost of properly rebuilding race version of an “F” engine is outrageous. They’re also much more complicated and require tools and equipment that many of us don’t have.

As far as the rule of thumb about a 4 stroke needing double the displacement to match the power output of a 2 stroke I think that’s outdated info. A modern 250-F race bike makes more power than a 125 pinger and a 450-F race engine will tear the decals off a 250 two stroke as it wheelies past it. Reliability and cost be damned, modern race four strokes are impressive beasts.



If I weigh the benefits of either design as it applies to my riding situation it's like this...

My outdated KTM 300EXC 2 stroke makes about 50hp and 40 pounds of torque.
The sister four stroke of the day, the 450EXC made 42hp and 38 pounds of torque.


On the 300 I can get up to 150 hours on a set of rings and 300 on a piston. The crank and rod on my oldest engine has seen 3 pistons come and go over the last 7 years of use and is still good.
I see the 450’s smoking by 400 hours of moderate trail/endure riding and then they get sold off for $2,000 rather than rebuilt.

So a top end on my 300 engine costs me about $300 and 3 hours working at a leisurely pace while watching a hockey game and sipping on rum. If I needed to do the crank it would take a day and add another $300.
If I owned the 450 and wanted to do just a piston and rings the cost would be about the same, but I’m sure the time would go up and I may have to lay off the rum to make sure I don’t screw the timing up. Now if the valves and crank were spent things change a lot. Cost would be in the $1,500 to $2,000 range and I’d need to ship the head to the US. My riding time would be diminished as would my bank account, but the engine would likely last me another 400 hours and even more if I would do the rings somewhere around the 200 hour mark.

So up to this point the 2 stroke looks a lot cheaper and has a better bang for the buck, but there are other factors to consider. For example, the cost of the fuel & oil. The following is based on 100 hours of riding at an average speed of 20mph.

300
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/25mpg = 80gal. X $2.00 = $160
2 Stroke oil cost per gallon = $1.25 X 80gal. = $100
Transmission oil = $10 X once per 100 hours = $10
Total cost to ride for 100 hours is $270

450
Fuel @ $2.00 per gallon = 100hours X 20mph = 2,000miles/30mpg = 67gal. X $2.00 = $134
Engine oil @ $7.00 per liter = 1.5 Liters X 20 hours = 7.5L X $7 = $52
Filter(s) $16 = 5 X $16 = $80
Total cost to ride for 100 hours is $266

So much for better fuel economy and not having to mix gas equating to lower four stroke operating costs. That fancy synthetic 4 stroke engine oil and frequent oil and filter changes the high power thumper needs eats it up.

Consider this as well:

You're stuck in a swamp and overheat and seize your engine. If it’s a four stroke you’d best start walking back up the trail to look for a quad to pull your broken bike out of the mud. If you have a 2 stroke you can just wait 15 minutes for the piston to cool off and kick it loose. Depending on how you ride you may not even notice a power loss and you could keep riding it until your next planned rebuild.

Now let’s say you’re a “ride till it breaks” guy. If you do that with a high powered 4 stroke the moment it “breaks” it will may take the head and cases with it, so your best bet is to part out what’s left on eBay when it happens. If you do this with a 2 stroke odds are the only additional cost to fix it that you’ll incur over a normal full rebuild when it “breaks” is to get the damaged cylinder plated, or sleeved.

Here are a few more comparisons:

The 300 starts first or second kick hot or cold. Kick starting a hot 4 stroke can lead to suicidal thoughts
The 300 weighs less that the 450
The weight of the 300 engine is situated much lower in the frame

So when I add up my two cents of opinion and calculations I think I’m better off spending them on a 2 stroke for how & where I ride and for my level of mechanical aptitude.

You forgot the most important part. Two strokes are fun as hell to ride!!!

[Ghostv2]

You forgot the most important part. Two strokes are fun as hell to ride!!!

That's anything with a motor.

[RubberSalt]

you forgot the most important part. Two strokes are fun as hell to ride!!!

bbbrraaaaaaaappppp!!!!!

[TwiZ]

This is a cool thread. Besides weed eaters and my huskuvarna and homolite chainsaws the only 2 smokers i ever owned was a old kx400. I was like 15 yrs old,cant remember the year but the exaust ran down below the frame and had dual shocks in the rear and it was freakin turbo fast,but never been much for bikes so i sold it. About 6 months ago i got a polaris 250 trailblazer that needed work for $300. I put new rings and bottem end bearings and seals,rebuilt carb and put a different primary clutch with heavier weights to make low end better along with a 11 t front sprocket,engine as basic as it gets,its abit of a turd, i bought it for my girlfriends son and its perfect for a 12yr old,and has proven to be very reliable.It will use 2-3 gallons of fuel (plus the cost of mix oil at $10 a quart) compared to my X using about half gallon to a gallon tops. Any of my friends that ride their 250 R or dirt bikes usually gotta break off early because they run out of fuel after a couple hours. Ive always prefered a 4 stroke,love the sound,for the trails we run you can lug em down where a smoker is in and out onthe clutch. So for me and where and how we ride i prefer a 4 stroke. I do have a question for the two smoke guys...would the polaris benefit from a pipe to get a lil more snot out of it,basically is the cost worth the gain?

[Mosh]

I personally have no interests in the 4 stroke versus 2 stroke category, as each has their own merits. and call me an old fart resistant to accept any new changes, but as being a professional auto tech and mechanic for almost 30 years, there are some designs that just never will be as bulletproof reliable and easier to squeeze power out of as back in the days of old. Personally, there is really not much room for improvement on a 250R engine, banshee engine, or even rock solid blaster engines and the like. sure, there are ways to bolster more power and efficiency, but usually that comes with a sacrifice of dependability.

I personally have seen some bone stock 250R blaster, banshee and older air cooled 4 stroke, engines be opened up for the first time in over 30 years in some cases. I personally have gotten over 10 years on some of these engine configurations without a rebuild. The same could be said for the old 300/250x 4 strokes and XR based 4 stroke engines.
While their is light years in improvements in power, weight reduction, etc, with newer designs, personally I don't feel many things are built near as well as what we have seen in the years past. And that is not limited to just ATV's. You can have all the technology in the world pushed into something, but when the raw materials are a fraction what they used to be in quality from decades ago, stuff just does not last, nor is it near as rebuildable as older stuff is.
The days of us seeing washing machines, small blocks, atv's and other items rolling off the line and still pumping after 20-30 years with limited service, are gone.

[RamsesRibb]

As far as the rule of thumb about a 4 stroke needing double the displacement to match the power output of a 2 stroke I think that’s outdated info. A modern 250-F race bike makes more power than a 125 pinger and a 450-F race engine will tear the decals off a 250 two stroke as it wheelies past it. Reliability and cost be damned, modern race four strokes are impressive beasts.

I don't think that is a fair comparison. You said yourself that your KTM300 was outputting more HP than the comparative 450 at the time of manufacture. I dare say that more energy and research has been placed into the current crop of 450 racers pushing it to a new pinnacle. That doesn't mean that equal increases are not possible on the 250 2strokes. I just finished watching endurocross and it appears as though even on a tight ultra technical track the two stroke bikes are easily capable of winning over 4 strokers. I'll bet that most of the focus to superiority of 4 stroke bikes was purposeful when the factories pushed their new products in the 90's. More money to make from parts is my guess.

On a side note, I don't know how common knowledge this is, but Mr Soichiro Honda despised the 2 stroke engines that he was manufacturing because of the noise and smell. I wonder if that belief was passed down?

[RamsesRibb]

I personally have no interests in the 4 stroke versus 2 stroke category, as each has their own merits. and call me an old fart resistant to accept any new changes, but as being a professional auto tech and mechanic for almost 30 years, there are some designs that just never will be as bulletproof reliable and easier to squeeze power out of as back in the days of old. Personally, there is really not much room for improvement on a 250R engine, banshee engine, or even rock solid blaster engines and the like. sure, there are ways to bolster more power and efficiency, but usually that comes with a sacrifice of dependability.

I personally have seen some bone stock 250R blaster, banshee and older air cooled 4 stroke, engines be opened up for the first time in over 30 years in some cases. I personally have gotten over 10 years on some of these engine configurations without a rebuild. The same could be said for the old 300/250x 4 strokes and XR based 4 stroke engines.
While their is light years in improvements in power, weight reduction, etc, with newer designs, personally I don't feel many things are built near as well as what we have seen in the years past. And that is not limited to just ATV's. You can have all the technology in the world pushed into something, but when the raw materials are a fraction what they used to be in quality from decades ago, stuff just does not last, nor is it near as rebuildable as older stuff is.
The days of us seeing washing machines, small blocks, atv's and other items rolling off the line and still pumping after 20-30 years with limited service, are gone.

I agree with the reliability issue. I have a stock 1980 ATC110 which is still running ok. It leaks all over but no smoke and still has good power. I also had a 185S which was never opened up as long as I had it which would be early 2000's. Same with my dads 93 Fourtrax 350. I had to did a rat next out of the air box but never had to open the engine.

That being said, this thread is not really a which is better match. I meant it to be informative about the research and development of this technology and just a current state of the industry. I don't believe we are getting all that is possible concerning 2 stroke technology.

[RIDE-RED 250r]

We might not be getting all that is possible in 2-stroke tech in dirt bike and ATV world, but other industries previously mentioned absolutely are. ETEC direct injection, stratoported chainsaws being top on the list.

[RubberSalt]

We're building better machines, but pushing them very hard. If we built our 450s with the quality of metal from the 80s, there a good chance the life span would be cut by atleast 30%. It isn't the quality, it the level of stress were pushing on them.

The 350x was around 26hp. But the 450r is around 46hp. Thats ~76% more power and only a 28% bigger motor. Get a 350x to push around 36HP and see how long it last. On pump gas!

[El Camexican]

I don't think that is a fair comparison. You said yourself that your KTM300 was outputting more HP than the comparative 450 at the time of manufacture. I dare say that more energy and research has been placed into the current crop of 450 racers pushing it to a new pinnacle. That doesn't mean that equal increases are not possible on the 250 2strokes. I just finished watching endurocross and it appears as though even on a tight ultra technical track the two stroke bikes are easily capable of winning over 4 strokers. I'll bet that most of the focus to superiority of 4 stroke bikes was purposeful when the factories pushed their new products in the 90's. More money to make from parts is my guess.

On a side note, I don't know how common knowledge this is, but Mr Soichiro Honda despised the 2 stroke engines that he was manufacturing because of the noise and smell. I wonder if that belief was passed down?

What’s not fair? Both examples were EXC models (Enduro X Country) and both were considered to be the pinnacle of technology for that class back in the day. Or better put, if I were to trade my 300 for a 4 stroke that bike would be the closest thing to a direct swap.

Fast forward a little more than a decade and the 300 now makes about 16% more power with an even smoother power band and the 450 enduro claims 20% more hp. The 2 stroke still spanks the enduro line of 4 stroke bikes, but it’s no match for the 450SX and it doesn’t need to be. The 300 has more than enough jamb for an enduro bike and so does the tamer EXC version of the two 4 strokes mentioned. I doubt we’ll ever see another 500cc 2 stroke mass produced. Very few riders could handle them back them, even some factory riders were detuning them, so what’s the point? Even KTM realized the 380 was overkill back in 2002 when they dropped it.

I have no idea what drove the Japanese manufactures to the 4 strokes, but I’m guessing it was a combination of all the PC correct global warming hype and the opportunity to cut the cost of R&D by putting all their attention on 4 strokes which make up all their street bikes, automotive affiliations, GP bikes, F1 programs etc. Keep in mind a lot of these companies work with others. The 5 valve engines from Yamaha and Toyota were a joint effort.

In the grand scheme of things snowmobiles and dirt bikes are a pretty small piece of the pie, but looking on the brighter side of things, the Big 4 stepping back from the smokers (and a strong yen) has allowed the Europeans to get into the game and build some pretty cool bikes. The more manufactures there are out there, the more innovation there will be.

[RamsesRibb]

I was referring to the 250 vs 450 comparison as not being equal footing. I inferred that your KTM comparison was a realistic comparison.

Also regarding the reliability of a 350x as compared to a modern 450, again totally unrelated but mostly due to the rotating mass and stresses created by the older designs more massive piston And less efficient timing system.

[BOB MARLIN]

To get back to the original topic, I had a boat with a modern 2 stroke outboard on it . It was a 225 Mercury "Optimax". It was direct injected and actually has an air compressor that was belt driven off the fly wheel that it used kinda like a blower on a car. The oil injector was computer controlled and could run as much as a 200:1 ratio. This engine would push my 26' off shore fishing boat well over 40 mph. It was quiet, sipped gas and was almost smokeless. I don't know what displacement it was but it was dyno'd at one of the shops I took it to and it put out just over 250 hp.

But the problem was that it was so "hi-tech" I just couldn't keep the thing running, and it was unreliable. When it ran, it ran fantastic, but it ended up spending so much time in the shop I had to get rid of it.

[RIDE-RED 250r]

I'm guessing they dynoed the Merc at the crank?? If so that makes perfect sense that it dynoed 250hp actual vs the advertised 225hp. Way back in the day, outboard motors were rated by crankshaft HP and sometime in the mid 80's they started rating by popshaft HP. So that's why it makes sense that your high tech modern Merc 225 was rated at 225hp (propshaft) and the actual dyno test showed 250 (at the crank). Sounds like about the right amount of loss from the power taking one 90 deg turn in the lower unit.. (If I'm correct in assuming they dynoed at the crankshaft)

Either way...interesting sounding outboard!