I've heard rumors that the absence of a muffler can burn up the valves in an engine. Is this true? If so, what causes this mechanically? i.e. the reduction in back pressure, too much heat, etc. Also, I'd like to take a stock SV650 can and shorten it by approx. half. Then powder coat it black to match the new black frame. Is this the same scenerio as not having a muffler at all? Will it ruin the valves?