Now that's what I'm talkin' 'bout. I have a McCullock 450 chain saw that I will be using the engine for my kart. The saw barn find I mentioned seems to have a broken ring. I made a crude measure of the diameter (across the piston) of this saw and compared it to the 450, and both measurements seemed to be the same. Both saws had the larege "pancake" style carb, but each carb has a different number. I dont know what determines the horsepower of these old Mac engines, but my thinking is if the piston is the same diameter and the carbs are very similar (only has different numbers) they should be the same horsepower and CC. I think the 450 engine , according to one source, is 5.5 cubic inches, and about close to 90cc. I am going to google this engine info again. The other engine I bought recently that has the broken ring has a larger (wider) surround at the carb area and a larger fuel tank, but the engine looks exactly like the 450 when completely disassembled. It does not look any bit different from the 450, but the I.D. plate was gone and absolutely no other numbers or I.D on either saw, other that the carb numbers. Does anyone know how to find out what this saw is. I can identify what the saw looks like. It has the starter on the crankshaft side and a black screen like cover over the flywheel side. It is not a geared saw, chain runs straight from the clutch to the blade, and the carb cover is wider than the 450, with the flange inside the carb area that the cover hold down screw threads into, is secured to the sides, not the top of the carb. The flange on the 450 fits over a machined -in bolt that is actually a part of the carb on top of the carb. The carb on the other saw does not have a bolt machined into the carb. Everything else is identical looking. If both engines are the same, then no use to replace the broken ring on the engine I just bought.