Is there such a thing as an 80cc 2 stroke?

Discussion in '2-Stroke Engines' started by bikejock, Nov 5, 2015.

  1. bikejock

    bikejock Member

    I know most vendors will often call their kits 66cc/80cc but from what I understand there's no 80cc 2 stroke that I can find anyway. They only seem to make them in the 66cc and under range. The only engine that comes close to an 80cc is the 79cc predator but that's a 4 stroke. I'm just curious though, has anyone ever made an 80cc 2 stroke bicycle engine? I imagine an 80cc 2 stroke bike would be pretty fast.

  2. butre

    butre Well-Known Member

    80cc is child's play, here's 800cc

    Last edited by a moderator: Dec 15, 2015
  3. bikejock

    bikejock Member

    Nice! Engine like that would never fit on a bicycle though.:icon_cry:
  4. crassius

    crassius Well-Known Member

    all the motors between 66cc & 69.4cc are 80cc when measured by the asian standard rather than the western standard
  5. butre

    butre Well-Known Member

    it's still 66cc by the asian standard, it's only 80cc by the vendors lying about their cheap chinese engines standard
  6. crassius

    crassius Well-Known Member

    haven't filled one with water to check, but I believe combustion chamber is 80cc
  7. butre

    butre Well-Known Member

    if I remember right a slant head is 7cc, meaning it'll be either 73cc or 76cc depending on whether it's 38 or 40mm stroke. the straight plug head on a 40mm stroke might be 80cc

    in any case, my theory is that the "80cc" thing came about as a misinterpretation of what the markings on an FM80 rod meant.
  8. bikejock

    bikejock Member

    That makes sense. Most countries rely on the metric system or some other alternative measuring system. I remember looking at a street tire I'm thinking of getting for my 29 mountain bike but in the description it says 28x2.1 when in fact it's a 29x2.1 tire. From what people say its because of a different measuring system the manufacturer went by.
  9. KCvale

    KCvale Motorized Bicycle Vendor

    For those that never learned geometry in school...

    No, there is no such thing as an 80 Cubic Centimeter 2-stroke engine in the bike engine context.

    Engine Cubic Centimeters (cc) DISPLACEMENT is measured in a cylinder by geometry math.
    The Volume of displacement is measured by the Bore width in centimeters of the cylinder * the Stoke length in Centimeters the piston can travel, period.

    The simple volume that can be displaced with the pistons movement in the cylinder.

    The head is where all the 66 Cubic Centimeters of compressed air/fuel mixture is shoved into and ignited.
    The smaller that area, the higher compression ratio and usually, the bigger the bang (power) you get.

    Most 66's are like 8:1 compression, that puts the heads CC size ~8.25cc give or take how your measure it, but regardless of size, the head IS NOT part of an engines displacement number.
    That is the Compression Ratio and what matters when the 2 numbers are combined.

    And just because something can displace more fuel mix does not make it stronger or better... All that is decided in the head by compression and spark timing and measured in any numbers of ways like Horsepower or Kilowatts.

    Heck, a 48cc sent up right with an expansion chamber and such will run with a stock 66.

    That's what really irritates me about the marketing BS specs and try to get others not to go along with it.
  10. butre

    butre Well-Known Member

    specific power is more complicated than just bigger=better. assuming two engines of different displacements but same build quality are both tuned to make as much power as they possibly can without exploding immediately, the engine with the larger displacement will likely make more torque, which means more power at a given RPM. that's especially true if only the bore is changed, and not the stroke. but then, a lot of racers destroke their engines, which makes the displacement considerably smaller, but greatly increases the RPM potential, meaning it'll still make more peak power, but at the cost of torque.

    there are a few guys boring out China girl jugs and sleeving them, usually doing 50mm bore which makes the displacement 78cc. I've heard of people going up to 52mm, which is good for 84cc, but from what I hear that requires a good bit of additional modification. Mark Clyde Stewart I think was selling 50mm bore jugs made by Bert Rod. Bert knows what he's doing, but he's the kind of tuner who keeps secrets, and since his stuff is out of my price range I haven't been able to get my hands on it to reverse engineer it.