Direct Injection and the Two Stroke

Oh no! Not another article about direct injection!

Of all the subjects talked about on the TSM forums, DI is the one that brings out the most emotion.

On one side you have the traditionalists that demand carburetors and on the other those who think DI will save two-strokes. Some even think DI as a technology will destroy the two-stroke.

How could DI create such an uproar?

Ossa DI 2 Stroke

First it would be helpful to understand why DI was talked about in the first place. Plain and simple because of upcoming emission regulations.

Regardless of your political leanings on the subject of emission controls, it’s here to stay and will affect our future. Regardless of the reasons for these regulations to be instituted, they will have an effect on new manufacturing of two-strokes (and four-strokes) in the future. This is how the world works.

Polaris 1200 Direct Injection 2 Stroke

So why is DI so high on the list when it comes to lowering emissions on two-strokes? Due to the inherent design of the current two-stroke, which allows a charge of raw fuel to escape through the exhaust pipe. This aspect alone creates the lions share of the emissions measured at the exhaust pipe.

The use of DI  eliminates this one aspect of the “dirty” two-stroke. Resulting in greatly reduced emissions on two-strokes. Instead of re-hashing the reasons here, take a few moments to read this article;

The EPA regulations state that vehicles manufactured for closed course racing do not have to adhere to these regulations. At first glance this is great news for two-strokes in motocross. That is until you discover that nearly 60% of the motocross bikes sold in the USA are used for recreation and not competition.

When this was brought up during EPA meetings with the manufacturers, there was no easy way to limit sales for competition use only. The move to four-strokes made this task easier in the short term, so that’s what the Big 4 manufacturers chose.

Is DI the savior of two-strokes? It’s difficult to tell the future without a crystal ball. Although from the information presented over the past few years,  indicates the addition of DI could extend the life of two-strokes for a few decades. Unfortunately using the carburetor configuration, only a limited number of machines from select small manufacturers or used machines will be available.

Arctic Cat 900 EFI Two Stroke

If it’s a choice between a DI two-stroke and no two-stroke, I’ll choose the DI every time.

DI kit for the Yamaha Banshee

Recent Related Posts

36 thoughts on “Direct Injection and the Two Stroke

  1. Agreed…DI or no two-strokes, then DI wins. Besides, I’m from the generation that got used to PowerCommenders on street bikes…tune the mix from the laptop. As long as we’re talking about…

    – a core motor with fewer moving parts
    – with cheaper rebuilds as a result
    – having much lighter weight
    – producing a far better power-to-displacement ratio than ‘diesels’
    – maintainable by anyone with basic garage tools and a laptop or I-pod that has the right connectors and downloadable software

    I don’t see the problem…count me in completely.

  2. Direct injection 2 Strokes creates a 4-stroke powerband.For most people that is better. But like I many people like that hit. With Direction injection you can have different power curves. It is possible to make a powerband that is narrower…than a current carborator2-stroke! Aprilia made a direct injection RS250 and did this. They had easy power curves like a 4 stroke, aggressivecurves, and curves that emulated carbureted2-strokes with that very hard hit harder hitting than today’s 2 Strokes. it would be very easy to have a switch on the handlebar that let the rider choose between them for his preference.

  3. A note on Christian’s comment. A wide powerband is not an issue if we get the greater power output at any diven displacement/weight. And, like Christian stated with Aprilia (and Suzuki on their GSXR line), mappable, programmable ignitions and injectors mean creating any kind of powerband you like, tailored to your riding style.

    My love of the smokers is just as much about the sound and power characteristics as anyone who experienced the piston-port world before case-reed induction. However my love of the sport means supporting lower-support-cost motors for amateur use, even if they don’t go “on the pipe” without some reprogramming.

  4. Wouldn’t it be easier to just do away with the EPA all together. After all, it was supposed to have a shelf life of only 10 yrs some 30+ yrs ago. It’s time they stick with what they say and just dissolve the department all together. Problems solved… All DI means to me is a more expensive bike with more crap to go wrong. Guess I’ll just be rebuilding my old bikes until I’m too old to ride anymore..

  5. I don’t know where the formal technical spec is that says that DI will end up providing a 4 stroke powerband. When a two stroke is “on the pipe” the pulses from the expansion chamber that reflect off of the back of the chamber push fresh air that is escaping from the exhaust port back into the cylinder before the port closes. There is nothing that DI can do to change this. DI can make sure the fuel/air mixture is more accurate at all revs and that may bring up power a touch relative to a carb at some points in the powerband relative to a carb equipped bike — perhaps this is what people are referring to?

    It is true that with DI the computer is in charge but said computer cannot change the laws of physics. Now if you program that computer to limit ignition advance in a stragegic curve when the exhaust pulses would otherwise cause HP to jump, then you could flatten out the curve — but that would be a design decision, not a design limitation. Also, if one manufacturere did something like this and reduced the power at certain places in the rev range to emulate a 4T, another manufacturer could decide not to do the same and therefore be making more power. I think the “market” would provide whatever curves the consumers would want.

    Count me in for DI if I can have to 2T trail/enduro bike and ride it year round in CA.

  6. I don’t think that the Ossa is DI. DI feeds into the top of the cylinder and not into the case as seen in the photo. I think that it is FI only.

  7. Hey there Rob. I think where the “4-stroke like” thing comes up is that a greater/smoother spread of power can be had due to variable ignition timing, variable fueling, variable exhaust port timing and (in some cases) variable intakes.

    All of these, along with a chamber tuned generally well enough to handle all of these variables, can keep a motor “on the pipe” for such a range that the power becomes quite linear…maybe not to the level of a four-stroke in general, but definitely to the point of a “cammy” four-banger.

  8. DI creates a powerband like a 4-stroke because of the same reasons it reduces emissions and fuel consumption. A car 2-stroke has bad fuel/air mixture at low rpm when it is designed for peak power. DI can provide good air/fuel mixture at both high and low rpm. This is can get you really close to a 4-stroke powerband. The rest is up to porting, pipe design, head, and a few other things.

    But like Christian Arnold said, you can have multiple maps that can provide anything from mild to wild to suit your style.

  9. Also, the Ossa is not DI. It is FI. FI fixes air/fuel mixture problems but not blow through.

  10. What is the Polaris 1200 DI? I have never heard of that engine and i would love to find out more about it and the vehicle it was in. Anyone have info on it? I didn’t know Polaris had DI 2-strokes yet.

  11. Like it or not, if we are to keep/save the 2 stroke, this is what they will look like. It is working fantastic in the sled and outboard industry. It will be possible to control how they “hit” in regards to their powerband as Christian has said.

    The things that make 2 strokes so wonderful are their simplicity, low cost and ease of maintenance and for the naysayers and or those who do not like to adapt to the latest “new” thing, should take heart. I remember years ago when this same kind of talked was being kicked around in regards to electronic ignition. That technology has done wonders for all makes and engine types and will do the same for 2 strokes with DI. I just hope that the engineers keep as their mantra, these simple words. 2 strokers like it “simple, easy to work on and efficient”, all things that endeared us to smokers in the first place.

    Nope, my smoke filled eyes friends, this newset techology is not the enemy, what we have before us is the future and we need to embrace it to move forward.

    However, while this tech is going to take us into tomorrow, it will not be what saves and powers the almighty as a final rendition/savior. This will be……

  12. “The move to four-strokes made this task easier in the short term, so that’s what the Big 4 manufacturers chose.”

    Are you sure that’s why they did it?

  13. i don’t know where you get the idea that DI 2 strokes have a “powerband” similiar to 4 strokes. They idle like a 4 stroke perhaps. But the design of a modern 4 stroke is a hugely oversquare bore/stroke so the engine can rev, and where it finds its horsepower. A 2 stroke does not need to rev to find its horsepower, and that doesn’t change with DI. Will DI fill in gaps in the torque curve that a carb’d bike won’t? Yes. But by all means, if you want DI to have a light-switch powerband, just program the electronics.

    Go to youtube and view the Ski-Doo 800 etec. The DI loses none of the agressiveness of the carb’d 2 strokes. It only loses smoke and emissions

  14. @Chris, I think we are talking the same language, the point(s) being made are that the powerband can be changed to soften the hit for someone who wants an efficient ( MPG ) bike mon. thru fri. and an asphalt scorcher on the weekends, or in the woods trail riding and racing the same machine. The racing sleds are able to do this with a program change by adjusting the powervalves, the ignition timing and fuel injection delivery with a DI system.

    The 4 stroke powerband comment I think is misplaced, I understand the intent of it, but I think the point ( comments ) were to make a 2 stroke more tractable like a 4 stroke and this would be possible. However, most of us strokers love the hit of a 2 stroke, et al. But it will really be the best of both worlds. Besides, if we can use these points to “sway” some of the ( lost ) 4 strokers back, more power to us.

  15. I do not want a 4 stroke power, that is the reason for owning a 2 stroke.

    ‘You can’t get blood from a turnip’…

    The entire 4 stroke debacle has FAILED miserably, I have never seen so many race-bikes 2-3 years old JUNKED and selling for $200-$400 and they cost $6000-$7000 brand new!

    When it costs $2000-$3000 to rebuild a 250F/450F when they gernade and the amount of money/time wasted on valves, cam-chains, cams that get smoked. Cranks that go out, cylinder heads, holes in cases. You have to ask yourself, who is the who made the poor choice in buying a 4 stroke bike…

  16. Suzuki_RM250_owner
    The reason for buying a 2-stroke is NOT the powerband. (way more people buy enduro 2-strokes than MX)
    The reason 2-strokes are great is that they are light, powerful, reliable, cheap, and easy to maintain. You may like that powerband, and I do in some cases, but most 2-stroke buyers do what they can to eliminate that, and that is the sole reason 4-strokes took over.

    DI will keep all the top end power(increase maybe a couple), but will much improve the bottom end. This will produce the flat torque curve of a 4-stroke. This gives more power down low(improved acceleration).

    Now you say you like the carb powerband. If you read previous comments you would have read that it is very easy to have multiple tunes, even ones that result in peaky powerbands. So you won’t lose anything.

    You also need to understand the difference between torque curve and power delivery. While you can get a 2-stroke with the flat torque curve, it will still have the 2-stroke power delivery. It fires every revolution as opposed to every other. Less time between power strokes means less time for the tire to hook up. This is what causes the rear wheel steer of 2-strokes.

    So even if you had 4-stroke powerband, when ridden on the pipe, you probably wouldn’t know the difference between DI and carb.

  17. You said it. Steering with the rear wheel. I can’t ride 4 strokes nearly as well because they push the front tires instead of sliding the rear around. Just don’t like em. No sir… I need my instantaneous flick of the clutch steering to go fast..

  18. Let’s just hope that when the “good technology” is added that there isn’t a push to add stuff that will really ruin a two-stroke…traction control. I thought I saw articles about Honda testing adaptive traction control on some of their supercross/motocross bikes.

    Steering with the rear wheel would be gone, eliminating the skill advantage of those who aggressively “square off” corners. The average could run with the aggressive, and two-strokes really would behave like four-strokes.

    I could see a manufacturer that doesn’t like “dingers” doing just that should DI two-strokes come into mass-production from anyone.

  19. @DingerJunkie – that’s one of the big complaints in MotoGP. Big 4 strokes + traction control has allowed anyone to be competetive. Guys like Rossi, who run on the edge, are disgusted by the electronics and the way they even the competition.

  20. @DingerJunkie:

    Honda has had traction control from 1998 IIRC, even if it has been a rudimentary form of it.

    What’s funny is now Kawi and the like are jumping on the traction control fun even though it’s still illegal in the AMA, thats one “tech” I do NOT want on my dirt bikes. I have a feeling most MX bikes have had it for a while, though it just wasn’t advertised so much (Honda advertised it when they first introduced it and then never mentioned it again, even though it was always there).

  21. I ride snowmobiles and the the DI-tec twostrokes are light, powerful and explosive. The 4-strokes are heavy and slow… And they are similar in fuelconsumption and exhaust pollution.

  22. Hi all,
    I’ve just sold my KTM 200EXC 2009, and have put in an order for a 2012 KTM 250 XC. Seems like a great alround bike. Whiel researching it, I came across this interview. About halfway through tehy ask about direct injection on 2-strokes and they confirm that KTM are testing and perhaps looking for suppliers. So we may not have it on the 2012 bikes, but it will come in time. Once it is fully tested.

  23. theyve been saying that for 3 or 4 years now buddy….

    one day… but Im not going to hold my breath

  24. I want fuel injection of some type for my cr500! tired of rejetting when i ride at different altitudes.

  25. i dont care what kind of motor it is as long as it sounds like a 2 stroke.

  26. @ serpent moves you would really waste your money on a 4-choke if it sounded like a 2-stroke?!? Come on you’re on TSM’s site & we all support 2-strokes 100%!!! That statement you made was just dumb.

  27. An article in Scientific American mag said that the millions of small engines
    used in 3rd world countries each emit copious nasty stuff. What good does it do to regulate the relatively few engines in the USA? The EPA once again performs rectocranial insertion!

  28. Em 2-STROKES

    twice quick, twice as powerful, twice as much fun!

    of course a 4 stroke isnt going to out do a 2 stroke

    halleluyah for DI cant wait to buy a kit for my rd 350 or rz 350 depending were you are in the world.

    Its better for the enviroment half the size engine for same power of 4 stroke less weight, smaller engine, less parts, eaisier to maintain!

    so 2 strokes will be around for ever.

    now with DI and all that micro chip stuff cant wait to turbo or supercharge as well!

    help the world and carbon foot print buy perfecting the emissions of the 2 stoke !!


  29. I owned a carbureted 2009 KTM 300XC and I felt the bike had a lot of 4 stroke traits thanks to the ignition curve and power valve spring adjustments. I sold the sucker. The one thing that changes is that the power delivery is limited to within approx. 3000 RPM from 5000 to 8000, whereas the 4 stroke can rev to the moon. Making a two stroke rev like a 4 stroke I dont know if its possible even with DI etc.

  30. To Richard Brokaw, did you actually run out of power on the 300? I’ve spent a lot of time on 450s and 300s. A 300 will outpower a 450 pretty easily; it doesn’t need to rev to the moon. Again, this is probably why 450 motors explode.

    The Ossa is not DI. DI goes straight to the cylinder. The Ossa’s injection goes into the crankcase just in front of the reed cage. Its kind of a hybrid of port and direct injection. There is still a substantial amount of fuel blowing out of the exhaust, which will still cause emissions issues in more strict areas. Though the bike runs on 100:1 which helps tremendously with emissions. Ossa is making a step in the right direction, and I love their bike.

  31. @gus zap. That’s a very silly comment, you’re a developed country. For this assume that global warming is true science fact (whether or not you believe that it’s the reason for emissions control). To cut emissions globally, developed countries need to be the leaders in cutting emissions. Countries like china are developing rapidly, and their cheap labour means they have insane amounts of industry that polutes, unlike the larger technology and finance sectors of developed countries. I’m not being condescending, you most likely already know this, move with the times!

    I’m seriously excited for DI 2 strokes. The tech is mature in the general automotive IC market, it just needs to make the price point for the bike market specifically.

    Also, someone was arguing that DI 2 strokes wont improve the fuel charge escaping, the idea is that the point at which the fuel is injected can be altered, so that it is injected as / when the exhaust port is closed. The later it can be injected in the cycle before ignition, the less escapes. There is obviously a trade off with the air fuel mixture’s ‘mixing’ / homogenity.

    Ossa are making a serious statement with their bikes, and KTM have been claiming investment and testing for a long time. Exciting times for 2T in the next few years!

  32. Rob C:
    When a two stroke is “on the pipe” the pulses from the expansion chamber that reflect off of the back of the chamber push fresh air that is escaping from the exhaust port back into the cylinder before the port closes.

    Completely correct Rob, but with DI, you could inject after the exhaust port has closed, providing you have a means of oiling the bearings and pistons.
    That way, its not mixture escaping into the exhaust, its just fresh air. And fresh air has no NOX, CO2, CO or particulates that I know of…
    I did hear rumours of an experimental motor that does this, oil pumped main bearings, and a feed into the crank that feeds a metered amount into the big end (which is a sealed bearing) up a hole in the conrod and into the smallend, and out through the gudgeon pin into a gallery around the piston ( which had three rings- a pressure ring and two oil rings.)
    What I heard was that it was a total loss system for the top end, feeding a small shot of oil out with every rev, although the mains ran in the same oil as the gearbox. Which would mean that you wouldn’t do the old sieze on the overrun/when downchanging trick… (I raced 250 production streetbikes when NSR/RGV were all the rage)
    If true, this design would still have some problems with particulates etc from the total loss oil system.

Leave a Reply