Anyone in here know how long the R.R. Merlin 66 could run at 3000rpm (or just 3000rpm) before it overheated, this would be on the Spitfire Mk. IX with automatic radiators. And if anyone know please tell me at what altitude to!
I think you're wrong concerning the Mark IX. As far as I know, that Spitfire was powered by a Merlin 61, not a Merlin 66. Unless there is a variant of the Mk. IX that I don't know.