Maybe I'm weird, maybe not. Both of my 4-cycles have a distinct smell that seems very different than the 2-strokes. Granted, I don't run much nitro in most of my engines so I don't know if that may be why I notice such a difference. I know the combustion process is hotter in a 4-stroke so it would make sense that the oil coming from the exhaust is hotter is more of it is burning versus a 2-stroke that tends to spit more unburned fuel out the exhaust. I am curious to hear what you find out.