Got one laying around?- don't want to take the head off mine What is the diameter of a 66 aka 80 cc piston? the 50 I have out here is 40mm at it's widest point-

What do you mean....Nobody?? Bought this,http://www.harborfreight.com/6-inch-digital-caliper-47257.html this past week on special. $10.00 + tx. Just so I can answer questions like this (and anything I might need to measure). It's my first use of it. A 66cc piston diameter is 1. 47 mm 2. 1.85 in 3. 17/9 or 1-8/9 in

Thank you or 117.5% of surface volume of the 50cc piston. So it stands to reason, if the stroke is still the same- and boygofast at least seems to be advertising the same bottom end for both engines- at least with 6mm studs- the 66cc is 117.5 percent larger than the 50cc, or then actually 58.75 cc? What am I missing here?

Here's some math- correct me if I'm wrong- and I don't know the depth of the stroke or the formula for cubic cc's but isn't the surface volume of a piston head pi x radius squared? 50 cc motor- 40mm diameter means 20mm radius 20 x 20 (squared)= 400 400 x pi or 3.14= 1256 square mm. "66" motor 47 diameter means 23.5 radius 23.5 x 23.5= 552.25 552.25 x 3.14= 1613.4065 square mm the second figure should be roughly 117.5% ? This is the surface area of the piston heads It's obviously not - it's almost another 1/3 again- or 33% more- so I guess I'm leaving the pi r squared formula off the percentage figure. 33% more then gives us an 18.888 figure- making the motor, with the same stroke- actually a 68.888 cc motor but of course I've roughed up on the figure to 33- it's not quite and I'm through doing math for the night. so anyway it's then a little bit LESS than 68.888 cc so maybe 66 is pretty acurate I think interesting