Compressor surge is a condition caused, generally when a car with a turbo has a BOV that fails (or no BOV at all). When the driver slams the throttle plate shut, there is still compressed air in the charge pipe.

The turbo, however, has no power to spin, b/c theres no load on the motor ( ~0-5% TPS) so theres no exhaust.

This causes there to be more pressure on the turbocharger to backspin than spin in a forward direction.

I do not have *tons* of handson experience with it, but my take is that the turbo will "surge" making a kinda 'wub wub wub wub' sound (I've heard this) and go between spinning forward and backwards with the unequal pressures.

This causes massive amounts of turbo lag when you get back on the throttle and absolutely DESTROYS shaft style turbos


The other way surge can happen is if a compressor wheel (the cold side) is required to move a volume of air far beyond its capacity (outside the islands on a compressor map, past the surge lines). A similar phenomenon occours, except instead of backspinning the pressure generated by the turbo will oscillate. I have never personally had this occour, and can't say with any assuredness it makes noise. I would guess that it is not only noisy, but makes your boost gauge go psycho.