The 85 engine has interchangable parts, but the cylinder and ignition are different, and the 85 is faster, but hits harder and is a little harder to ride. Also, the frame is different then the 80. The steering head is pulled in, and the linkage is different on the 85. IMO the 80 is a better trail/play bike, and the 85 is a better racer for a good rider. So, they're almost the same. As far as CC's the 85 has a .5cc or so difference.