I want to thorw an idea out there for those who think that cold air is going to kill your exhaust valves.
I run antique farm engines under full load. Many of these govern themselves by holding the exhaust valves open between firings when idling. Many of these engines have hot heads (no coolant in the heads). most of these have no mufflers. I have gotten the exhaust valves red hot under load, fire out the exhuasts and everything. As soon as you take the load off the engine, fires only when needed and coasts pulling cool air through the valves. These valves are not modern sodium filled and all of that. They are plain hardened steel valves. I have never warped one through all of this.
I know these aren't high performance engines, but it is something to think about.
Correct. In the early days, before header technology changed the way things were done, we used to run open exhausts on dragsters, circle tracks, and some even on the street. Usually there was about three or so inches of exhaust pipe, and that was mainly for looks, some didn't even bother with that. The mechanics would watch the flame in the cylinders for tuning the engine. They wanted a nice blue flame. These engines were basically stock, some with a few modifications. We would run them for several seasons without problems. When problems did occur, it was from leaning out and burning stuff up.
Also, when the engine is ice, ice, cold, and you start it up, there is some pretty hot stuff going past that ice cold valve. shady