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by aarsas j on October 5th, 2005

aarsas j

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What are the advantages and disadvantages of a 4-stroke engine compared to a 2-stroke engine?

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Answers. 4 helpful answers below.

  • by Chuquilson on September 22nd, 2008

    Chuquilson

    What I can contribute is that 2-stroke scooters let out about the same pollution per mile as most cars- newer 4-stroke scooters let out significantly less pollutants per mile driven.

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  • by riverrock on September 22nd, 2008

    riverrock

    But which one is better?!? Of coarse "we" 4-stroke people say 4-stroke, but do you know why?? Probably not, so I'll explain. First I'll name some of the advantages of the 2-stroke engine over the 4-stroke engine.
    • When the engine is revving at 10000rpm the 2-stroke engine ignites gasses 10000 times per minute while 4-stroke engines ignite only half. So it should have twice as much power, right?
    • The 2-stroke engine does have channels for air transport but the piston opens and closes the channels, in a 4-stroke engine there are separate valves and a camshaft that do this. This means extra moving parts and a far more difficult cylindered design. Because of this maintenance is more difficult.
    • 2-stroke engines give more power. At 50cc races 2-stroke bikes can reach speeds of over 130km/h while 4-stroke bikes can hardly reach those speeds with 70cc!! The same applies to everyday use. When you remove some restrictors from a scooter it will go 80km/h. You won't reach these speeds with you're 4-stroke bike by just removing some restrictors.

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  • by 8 Jan 2004-10 Dec 2009 on October 11th, 2005

    8 Jan 2004-10 Dec 2009

    One advantage that 2-strokes have is that they need no lubrication system; no oil pump, simpler design due to not needing oil passages, etcetera. However, this requires adding oil to the gas as 2-strokes rely on the fuel for lubrication. A nice side effect is that 2-strokes can run at any angle (sideways, upside-down..). so long as they can suck in fuel. Try that with a 4-stroke and you might seize it.

    Another advantage of 2-strokes is that they make more power relative to their displacement because each cylinder has a power stroke every 360 degrees instead of every 720 degrees. Of course, this means that they suck in fuel on every piston stroke instead of every other piston stroke, so fuel efficiency may suffer.

    2-strokes are prone to the same problems as Wankels with regards to fuel consumption and emisions as both rely on the moving part and stationary ports (either piston/cylinder, or rotor/housing) for "valve" timing, though modern technolgy and QA procedures are reducing some of those issues. OTOH, not needing a camshaft or valvetrain does have advantages in both engine weight and reliability; fewer parts = less to screw up.



    I have also heard of a new engine type that is a hybrid of 2-stroke and 4-storke called the "Z" engine - http://www.aumet.fi/ . You might find it VERY interesting.....

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  • by maddock on October 10th, 2005

    maddock

    Real briefly..

    2 stroke engines

    Pros:
    - Run forever with little maintenance
    - Simple to troubleshoot
    - Very inexpensive

    Cons:
    - Run dirty and pollute the air
    - Usually are loud
    - Oil must be added to the gasoline in a specific ratio
    - Can be very hard to start when cold

    4 stroke engines

    Pros:
    - Very dependable
    - Run much cleaner than 2 strokes
    - Can be made to run very quietly
    - Can produce far more power than 2 strokes because they can be made much larger

    Cons:
    - More complex and harder to troubleshoot
    - Require oil to be changed regularly
    - More expensive than 2 stroke

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