ok so does your car have any mods at all? if you posted it and i missed it sorry! when you say blown piston what do you mean? rings, is the piston snaped in half, is there a hole threw it? i dont hear about to many n/a leaning out to the point of melting a piston unless thay have some major upgrades,realy bad tune, or major fuel system failure! did you brake in the engine after it was rebuilt? or did you go out and beat on it right away? that kind of a rebuild needs at least 1k miles to break in. if now ones responded to your question leaning out is lack of fuel in your air to fuel mix to much air not enough gas makes for way to much heat! in turbo and high hp n/a you start to melt threw things! theres not an afc on your car is there?