My 69 Firebird 400 with it stock replacement (Gardner) exhaust. It had a nice rappy snarl to it. My stock Fuelie 283" 283 HP Bel Air was the one I loved best. The clatter of it .008 and .018 lifters, the piston skirts when they contracted a little bit when cold and the fuelie's whistle at idle. It was awsome!
A lot of 2-stroke diesels had a very distinctive sound. Detroit, Commer TS3, etc. So do Deutz air-cooled V8s, though 4-stroke.