it'll say the displacement on the sticker on the cover part that's over the muffler. if it is an 18cc, the port timing isn't that great... I had one that I wanted to run but it was too scored to run, I had it all ported and set up for gas/glow and realized the compression was too low to fire off (was at 60psi on the gage, and it just refused to start), so I'll use the crankcase to put another jug on at some point. this does end up being a light engine all set up though, I had mine down to under 2lbs with everything attached to it including prop, but I did kinda go extreme on trimming the jug...