actual displacement of 80cc kit(well almost actual)

Discussion in '2-Stroke Engines' started by dazed_maunder, Aug 28, 2008.

  1. dazed_maunder

    dazed_maunder New Member

    i pulled my head of today on my 80cc kit and did a few measurements,somewhat rough measurements as i'm in the us right now and my micrometer is back home but there very close,close enough to count anyways what i got for the bore size was roughly 1.84 inches and for the stroke i got 1.53 inches so bore x bore x stroke x .7854=4.06 cubic inches convert that 4.06 x 16.39=66.54cc
    so fore sure the 80cc's are not 80cc and please remember my measurements ar not exact just very close

  2. spad4me

    spad4me Member

    If its a kings engine they use the olde English method and use lines of barley corn, or the length of the king's thumb to measure that is why your measurement may vary from theirs.
  3. dazed_maunder

    dazed_maunder New Member

    well I used those red sticks off of bottle rockets a pair of scisors and a standard tape measure
  4. HI,

    Which engine (brand / supplier) did you measure?

  5. Maxx Ported

    Maxx Ported Member

    I measure my engines with a bore gauge and a depth mic. Thats Why the other day, I said each engine seems different. The bores are usually 1.850, but the stroke varies from 1.6 to 1.63..
    The most cc,s I have found so far is 71.18cc
    I hate being told I can buy 70cc OR 80cc, for the same price.. When I can't even measure one that large.:-x:-x... ( have bought over 40 engines kits)
    even the head bolts vary from 1.7 to 1.825 spacing and .130 to .300 diameter:confused:

    even had one box MARKED 80cc but IS a 49.18cc called to asked WHY?????? OOOOOOOOOOOo so Sorry. and nothing was done:-x:-x

    Why can't the TRUTH be TOLD:(

    Attached Files:

  6. HeHeHe.

    Thats funny right there.:grin:


  7. dazed_maunder

    dazed_maunder New Member

    engine brand supplier

    well Andy it was the 80cc kit i got it from powerkingshop on thEBAY,brand?who knows i have no idea who makes these things they all look the same
  8. HoughMade

    HoughMade Guest

    What is the volume of the combustion chamber? I'm convinced that what is being advertised at times is displacement plus the combustion chamber- that is "cylinder capacity", but obviously that is not the same as "cylinder displacement"- which pretty much all engine guys go by.
  9. dazed_maunder

    dazed_maunder New Member


    volume of a cylinder is height times area of the circle so area of circle roughly but closely being 2.65 and height being roughly 1.53 you get 4.05 inches its all the same convert that into centimeters and you get 66.36cc
  10. HoughMade

    HoughMade Guest

    I passed 6th grade math so I know how to figure volume of a cylinder- but that is not my question. Earlier, you said the stroke is 1.53 inches- that is not the height of the cylinder. That is the length of the stroke.

    The combustion chamber is the area above the piston when the piston is at top dead center....there is and must always be a space there. That space, plus the engine diplacement (bore x stroke) is the actual volume of the cylinder or cylinder capacity. However, engines are usually not measured in cylinder capacity or cylinder volume. They are measured in cylinder displacement.

    Unfortunately, many people use the terms "cylinder capacity", "cylinder volume" and "cylinder displacement" interchangeably- that is not correct. My theory is that the "80cc" myth is due to incorrect language more than a deliberate attempt to mislead. The displacement of the "80" is around 70ccs (or less), but the "cylinder volume" or "cylinder capacity" may very well be close enough to round to 80ccs.

    Of course to call it 80ccs is still misleading because everyone assumes it is displacement, but as we have all seen, the translation between Chinese and English can easily result in mistakes.
    Last edited by a moderator: Aug 29, 2008
  11. dazed_maunder

    dazed_maunder New Member

    so you are talking about the extra space between the piston and in the dome of the head being added to the cylinder displacement?
  12. s_beaudry

    s_beaudry Member

    Not to start a bigger fight with this....

    But to my reasoning, an 80cc HT is actually 65.92cc

    That is how I was taught to measure volume in terms of displacement.
  13. HoughMade

    HoughMade Guest

    I think we all agree with that....that's not the issue.
  14. dazed_maunder

    dazed_maunder New Member

    ok hough what about this,take the head off remove spark plug,drop the piston just a little from tdc fill the void in the head with clay and enough to fill down through the gasket to the slightly lowered piston then reinstall the gasket and torque the head down,turn the engine back to tdc excess clay will come out the plug hole then remove head and collect the clay minus what was in the plug hole and measure the volume of the clay then add that to the displacement reading
  15. arceeguy

    arceeguy Active Member

    I read somewhere that if you add the swept volume (bore x stroke) and the squish band, you end up with a "cylinder capacity" of close to 80cc. Someone even mentioned that the "effective displacement" is even less because they were only counting the part of the stroke when all ports are closed. (making things even more confusing!) It doesn't really matter to me whether it is a "true" 80cc, as long as it is bigger than the "48cc" engine. I am happy because I got an engine with more displacement. They all cost the same anyway, so I don't see what the big deal is. We're talking $99 bicycle engines, not $15,000 Harleys.
  16. Drunkskunk

    Drunkskunk Member

    You could do the same thing with water, or a heavy oil. Less chance of an air pocket, and you could do it without pulling the head off
  17. dazed_maunder

    dazed_maunder New Member

    it would be harder to collect,i know they measure the volume of heads with heavy oil or some sort of sand but thats when the head is off and that wont include the gasket space and the space the piston crown takes up either way this has turned into something it wasent supposed to be i gave a cc measurement based on the way most if not every engine is measured for displacement or volume (same thing) as for they might be different because there chinese or what have you i do believe a dirt bike from china would have the same cc reading as one made in the us either way i still am curious to see if the displacement plus the the combustion chamber volume would actually add up or even closely add up to the manufactures cc rating