The engine that I have is an ABN construction but near the top of the piston there is a groove with a brass looking ring inside it. I know its not an airplane engine. Its a race engine and it turns 43000 rpm's. Im stumped. The company that makes this one also has a high end .12 race engine for about $500. This one goes for about 250. Not that it matters but just to show its not a cheap engine. I would take a picture of it but I dont want to take it apart.