Gentlemen, I've been trying to find a reputable source for the cause of this but I'm having little luck. There seems to be a well known idea that running an engine with just open headers or just a collector with no long exhaust will eventually "burn the valves." The idea is that they warp and then lose enough contact with the head for heat dissipation. I've also seen people saying that exhaust leaks can do this also. The theory is that upon shutdown, cold air can reach the valves and warp them especially if they are open (unseated from the head). One counterpoint to this theory is that losing an exhaust causes the engine to run lean, and this is what actually causes damage to the exhaust valves. Does anyone know the truth behind this?
Also, during the valve overlap portion of the combustion cycle, isn't a fresh dose of cold air hitting the exhaust valve anyway?
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