Two-stroke engines making comeback

Suter MMX 500 two-stroke

Two-stroke engines were phased out by tough pollution laws and fuel economy targets, but they could be making a comeback with KTM, Honda and boutique builders.

KTM and Honda have both registered patents for direct-injection two-stroke engines.

In 2015, Honda filed a patent for a new two-stroke motor using direct fuel injection for a cleaner burn and better piston cooling.

Their patent injects the fuel close to top dead centre, after the exhaust valve has closed, so unburnt fuel doesn’t go out with the exhaust. The result is higher efficiency, less unburned fuel and reduced emissions.

Valve actuation is by pushrod, so it is unlikely to be a high-performance motorcycle engine. It is more likely to be employed in environmentally sound commuter bikes.

However, we are yet to see this patent being used in production.

Now KTM has filed a patent for a fuel-injected two-stroke engine that they plan to introduce to their enduro range from May.

The KTM system uses Transfer Port Injection with the fuel injected into the intake rather than the compression chamber.

KTM says the engine should reduce or eliminate unburnt fuel getting into the exhaust, which means a cleaner burn.

KTM's two-stroke patent engineS
KTM’s two-stroke patent

The system also dispenses with pre-mixing oil and fuel.

KTM will make 250cc and 300cc versions as early as May.

Meanwhile, German company Ronax and Switzerland ‘s Suter Racing are making super-expense two-stroke racers.

The Ronax 500 is powered by a fuel-injected 500cc two-stroke V4 with 119kW at 11,500rpm but weighs only 145kg (dry) with its aluminium beam chassis, banana-tyre aluminium swingarm and carbonfibre bodywork.

Ronax 500 two-stroke superbike engines
Ronax 500 two-stroke superbike

Only 46 will be built and the price is $144,000 plus taxes, freight, duties, etc.

Suter Racing has developed a 576cc two-stroke MMX 500 which blows the Ronax 500 away with 145.5kW of power and weighing only 127kg.

Suter MMX 500 two-stroke engines
Suter MMX 500 two-stroke

The undersquare engine (56 x 58.5mm) would also have a mass of torque.

It features a six-speed cassette gearbox, dry SuterClutch and tailor-made CNC aluminum twin spar frame and swingarm developed through Suter competing in MotoGP and World Superbikes.

Only 99 will be built and the asking price is $US123,500.

14 Comments

  1. What’s so new about all this? 2 stroke outboard motors have been “Emissions Complaint” for about 15 years now. So are 2 stroke snowmobiles. I’ve seen at least one bike built using an engine & infinitely variable speed transmission snarfed from a unsuspecting snowmobile.

    Apply Lateral Thinking.

    And, while we’re talking about advancing the state of the art using old technology, Bridgestone, (ya. The one who now build tires) built a beauty 350 twin with direct injection back in the 60’s. That’s direct injection into the main bearings.
    Apply only as electronic controls demanded = NO VISIBLE BLUE SMOKE!

    Suzuki T20’s etc. had oil injection back then but only dumped it into the intake manifold. Did eliminate the nasty old fuel/oil mixing however.

  2. Two strokes are dirty not because of unburnt fuel but all the oil they need in the fuel to keep from seizing up as there is no sump oil like in a four stroke. They get their boost in power over four strokes by having two power strokes every four revolutions as opposed to a four strokes one power stroke and from the fuel air mix being compressed in the crank case and forced into the combustion chamber.
    Cleaning up a two stroke mainly means removing the oil from the fuel mix and making the crank case dry by some form of sealed bearings and dry lubricants on the pistons. Direct injection or port injection has very little to do with it. A carby could do almost as good a job but EFI has benefits other than just making an engine cleaner.

    1. Have a look at cutaway diagrams of how the EMD 567/645 series of 2-stroke diesels work with wet crankcases. Hint: they would not run at all without a blower of some sort. Until they see one of these operate, most people don’t know how a 2-stroke can have a 4-valve head. It certainly got me curious.

    2. Al
      Two strokes fire every revolution. Four strokes fire every second revolution.
      I did like riding two strokes. Fast, light, easy to work on. My first was a Bultaco Metralla in ’69.

      1. I got strokes and revs mixed up there, sometimes when you’re trying to remember and think what to write at the same time shit happens.

        I was thinking that they might do a blower and wet sump combo but since they said push rod exhaust valve I thought dry sump and crank case compression most likely..

  3. First bike was a 2-stroke, & I discovered everything 4-stroke riders said about 2-strokes was wrong
    plus my bike was faster than all the equivalent sized 4-strokes.

    Ignorance is bliss.

    1. High RPM they always used rotary valves typically anything over 16,000RPM and below that they used reed valves. Then of course the simple ones used the piston as a valve, but a valve it still is.

  4. The Honda system sounds like it has the best chance of providing clean(ish) emissions. By the scant info provided here, I’m guessing the design is a petrol-powered derivative of the brilliant General Motors Electro-Motive Division 2-stroke diesel design dating back to the 1930’s and still providing sterling if not slightly dirty service.
    The KTM sounds like it is a conventional 2-stroke we know and love but with fuel injection tacked on. Piston and bottom end lubrication may still require an oil mist which is not at all cat-coverter friendly.

    Still it’s nice to see 2-strokes still being improved.

    If only some older road-going 2-strokes had the benefit of improved engine management.. The Suzuki RG500 was a wicked device in its day as many riders who encountered the cricket-bat powerband in the middle of a corner would testify.

    1. Rider gets a little too enthusiastic on a sharp bend, encounters wet leaves while riding the powerband, spins up the rear, loses traction, gets high-sided off into the bushes…
      There’s nothing quite like that slightly terrifying apprehension you get as you fire up a big stroker for a ride and it crackles into life. Especially on a skinny 120/90/17.
      145.5kW of two-stroke power in a 127kg bike sounds awesome, but for $125,000 I’ll stick with my 30 year old RG – which, incidentally, still gives today’s 600s a good run for their money!

      1. Actually O.J., no… 2T’s have very little inertia, & if you shut the gas, will not continue to ‘drive’, – or ‘engine brake’ like a 4T will… of course you need quick reaction times though..

        What you’d note as “apprehension” – I’d call a thrill of anticipation, since you have to be
        up to the demands of the quick responses of the 2T engine, which many cannot manage..

        4T race bikes require complex electronics & ‘slipper’ ( no back torque) clutches to deal
        with this same problem…

        Lets hope KTM does EFI 2T Duke road bikes – say, a 300 single, 600 twin & 900 triple…

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