Twist the key and the exhaust erupts with a ferocious bellow. In enclosed garages, it is a fearsome explosion that sets off car alarms and nasty looks. Out in the open, its thunderous note turns heads and raises eyebrows.

"This can't be legal" is your first thought.

The idle is too lumpy, too raspy, too loud. It's a dull rumble that becomes a guttural roar -- at quarter throttle. Declutch a cold engine and coast to a stop, and the exhaust crackles and sizzles -- the sound of raw fuel hitting hot metal...Continued