Most powerful exhaust I've ever heard was a Saturn V lifting off. If that doesn't count, I too miss the sounds of Matras, Alfa 33/3s and under-three-liter anythings at full song. Top fuel still amazes, so does a full-on NASCAR field blasting by. But in the modern era of sportscar racing it's got to be the Mazda 787. Those really did sound like a dentists drill focused on your skull.