It depends on the type and size of engines that should be researched. In Malaysia, 2-stroke motorcycle engines are common. In this way, you could take 1-cylinder 2-stroke engines with about 100cc displacement.
Engine friction is influenced by several factors, e.g. engine size, engine speed, load, materials, surface treatment, etc. In general, the friction of two stroke engines is lower than those of four stroke engines, because of the reduced number of moved parts (e.g. no valve train required). On the other hand, wear behavior of two stroke engines shows some disadvantages in comparison with four stroke engines because of the different lubrication concept (oil-fuel mixture), different engine bearings and the cylinder shape including scavenge ports. Because of the scavenge ports in cylinder, the piston and piston rings are exposed to increased wear in comparison with four stroke engines.