If you get to this year's Silverstone Classic, listen out for the Group C Mazda. That thing sounds as if it's travelling at a thousand miles an hour when idling and you can hear it screaming from the other end of the track.
In fact, it is usually driven by its owner at a somewhat less than competitive pace. When I attend, my car club is usually placed directly on the exit of Bridge. You hear this thing approach and expect it to come hurtling around the corner. But, instead, it sedately trundles past, its engine wailing like a banshee.
Far, FAR away from the best sounding engine. But, one not to be missed.