Best sounding engine I'VE heard...A fully built, race-prepped 1.8 liter Alfa Romeo 8 valve DOHC all aluminum 4 cylinder strung out at 8000 RPM. Music to my ears. (I guess I'm being partial because that's the engine my dad has in his Austin Healey Sprite.....) But man, I guess it's the fact that it's a roadster, but when he gets past 5k rpm, the thing just sings--sounds absolutely gorgeous!
I think any race-prepped 4 cylinders wound out at incredibly high rpms sounds awesome. (besides honda engines, of course :pface) I had a video of a Lotus Elise that must have been at 9000 RPM racing against a corvette on a road course--sounds GORGEOUS, especially with straight-cut gears.
I like the sounds of formula one v12's as well....
EDIT--found a sound clip of the 1.8 liter I was speaking of (technically a 1.95 liter)
beautiful