For those wondering, the average exhaust manifold/header operates at about 600-800 F [315-425 C] (your engine's combustion chamber reaches temperatures of 3,600 F [2000 C], albeit very, very momentarily). This glowing is usually the result of running at a high rpm for a continuous amount of time, usually after racing on a hot day or dyno-testing, and is actually not imminently dangerous to the engine.
