As many have said above - a Merlin (Spitfire etc great, Balliol at full chat incredible), two Merlins (Mosquito - beautiful), 4 or more Merlins together (wonderful) but best of all 4 Griffons on the Shackleton at max power and water meth engaged (80" of boost) - so long as you're outside not inside.
However, most memorable the sound of a Voodoo passing overhead and reducing power - almost frightening in its noise.