A type of muffler that is used for shitty cars (mostly rice burners such as toyota and nissan) that makes a very low-pitched hum. Shit whisltes are used to make the cars seem to have a sizable amount of power and/or speed. When rubber meets the road however, the car proves to be a heap of shit.
Dumbass: Dude, that supra sounds awesome! I bet that thing could tear it up on the quarter mile!
Smart person: No, that's just a shit whistle. The car will actually run about a 15 second quarter mile.