Lancman
The best engine sound ever as heard from the cockpit had to be that of four Merlins coming on song during take-off.
I can't speak for four Merlins but the loudest engine noise I have ever heard was four Griiffons from
inside a stripped out Lincoln I was quite moved by the sound of 8 Merlins when overflown by two Lancasters during the visit of the Canadian one.