Why 2-Stroke Direct Injection is a Big Deal

This article was written by Phil Mickelson at Snow Goer magazine. More in-depth information about fuel injection on two-strokes. While these are not motocross applications you can see how they could be adapted to MX bikes.

When U.S. Environmental Protection Agency regulations for snowmobiles started in 2006, Ski-Doo already had its 600 H.O. SDI two-stroke engine on the snow for two years. It was considerably cleaner than regulations required and it achieved industry-leading fuel economy. The engine was light, powerful, dependable and clean.


As the Bombardier Recreational Products (BRP) Evinrude group developed the E-TEC system for its outboard motors (BRP acquired Evinrude in 2001), it became clear that this technology could translate directly to Ski-Doo snowmobiles. In the winter of 2008, Ski-Doo released the 600 H.O. E-TEC engine.

Is the E-TEC engine a big deal in the world of snowmobiling? Absolutely. It demonstrates that the two-stroke engine — with all of the advantages it offers for snowmobiling — is far from being axed from snowmobile manufacturers’ product plans. The 600 H.O. E-TEC is available across Ski-Doo’s 2009 lineup and further expansion of the direct injected technologies will prove the strength of the two-stroke engine design and its attributes.

To read the complete article, please click on the following link;

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13 thoughts on “Why 2-Stroke Direct Injection is a Big Deal

  1. This is an amazing article. The two-stroke fuel injected engine with clean emissions seems to be in our future in motorcycles and possible cars if that 1000 cc two-stroke with 220 hp is possible. I love the dyno chart and believe that is easily possible to have the higher curve on the two-stroke curve over the equal size four-stroke. The question is though how useable is the powerband.

  2. With direct injection the powerband is equivalent to that of a 4-stroke. It is just as flat. A 250 2-stroke will have a powerband about the same as a 450 4-stroke. Just as much torque and power throughout the rpm range. So there will be no competition when comparing equal displacement bikes. And if a 250 has the same powerband as a 450 then the 250 has the advantage of weight and the 450 has no advantage.

    What this article leaves out is the 600 E-Tec makes 130hp and gets 21mpg. The 1100cc Yamaha makes 130hp and gets only 18mpg and weighs 85lbs more.

  3. Perhaps someone could answer this question:How much does the parasitic drag of the valve train affect fuel economy in a fourstroke gas engine? What I am wondering is if this is partially responsible for the amazing fuel economy ratings of some direct injected two cycle engines?

  4. The cleaner emmisions and better economy are definately good things. However, dont we ride 2 strokes because of how fun the powerband is and how simple the engine is. I can do a top end in an hour, and its so cheap relatively. And the biggest reason i ride a two stroke is because of the sensation i get when it comes on the pipe and tries to rip my arms out. Why would we want the two stroke to mimic the four stroke. Just seems like less fun and alot more complications.

  5. Nick1881
    I cant see why a DI 2t would have a flat power curve. The expansion chamber should work the same way and charge the cylinder as today. Just more power and less smoke…

  6. @Sachsgs250

    Exactly. There is drag in the cams, valves, and cam chain that the 2-stroke doesn’t have which is one of the reasons DI2t bikes get better gas mileage. The other is the less weight. I may have heard a 5% drag from the cams and such, but I may be wrong.

  7. @nick1881

    Only some people ride 2-strokes for the powerband. Most people in the world prefer a wide powerband, part of the reason 4-strokes took over. The main reason for riding a 2-stroke is not the powerband but the huge amounts of power that come with a very light weight bike. DI2T bikes retain the “on the pipe” characteristics of huge fun power, they just add tons of power to the bottom end. If you ride a bike on the pipe you are not experiencing the power hit and you can ride a DI2T the same way. It will still try to rip your arms out, it just won’t bog down in the wrong gear leaving you helpless up a hill or jump face.
    Most people are on the constant search to add bottom end power to their 2-stroke. One of my favorite bikes is the KTM 300XC because it has a wide powerband. I am trying to jet my 380SX to give it more low end.
    With DI you don’t have to compromise the on the pipe power for low end. With the 300XC I can ride all day in the mid range and at any time I can get on the pipe and rip up anything in my path. DI would improve the top end of that bike. It is just more options without compromise.

  8. @RM500

    The flat curve has nothing to do with the pipe. The Direct Injection is able to provide the precise fuel/air mixture at any rpm. A carb can only do so at about 4 different rpm’s. Adding direct injection will not increase your peak horsepower. But since DI cools the engine slightly and is injected after the compression the compression ratio is able to be increased slightly yielding more horsepower.


    Well DI snowmobiles still have expansionchambers and a ripping powerband.

  10. I like to give much for a onecylinder version of that e-tec 600 on a dirtbike bottom end and gearbox. Mounted in a KTM chassie… Can we have 55-60 hp from 300cc?

  11. DI 2-strokes would still have expansion chambers. The DI will give the 2-stroke a linear powerband and the pipe will be used to tune the powerband. Right now the KTM 300XC has a linear powerband. Expect a DI 250 to have the same powerband and peak power as that bike. Maybe even better.
    KTM makes 49hp in the 250SX and Maico makes 54hp in their 250. I figure a DI 2-stroke with increased compression could easily make 54hp+ with much more low end power.

    I wonder what the comparrison of E-Tec direct injection( High Pressure) vs Orbital’s air assisted Direct Injection. Especially for small engine sizes. Aprilia has an Orbital DI 2-stroke, 50cc scooter. The smallest high pressure DI right now is the E-Tec 600 Ski-Doo. (Evinrude has a 25hp 578cc outboard also)

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