I agree that the .455 is a better engine than the .46NT. Mine it totally reliable. I got it used. My .46NT ran slightly rough on the first tank of fuel, but was running great after that. I never had any problems with it, though I did notice that it kept getting smoother and stronger the next 4 or 5 tanks of fuel. Remember, these are chromed sleeves that are breaking in instead of nickel. It could also have something to do with the pinch between the OS and Evo engines....maybe, but I'm betting it is the chromed sleeves as they are much harder.