Which type of blow-off valve makes the fluttering or pigeon noise?
The short answer is that there is no blow-off valve that makes this noise. Read on to find out why. Without a BOV, the pressurised air being pumped into the engine by the turbo will have only one path when the throttle is closed: back through the turbo compressor. The fluttering sound is the sound of this air against the blades of the spinning turbo compressor as it tries to flow through it the wrong way. Car manufacturers fit recirculating (plumb back) BOVs to give the pressurised air an alternate path when the throttle is closed: back into the turbo compressor inlet. This eliminates the undesirable in a brand-new car’ fluttering noise. Aftermarket BOVs typically vent the pressurised air into the atmosphere for the purpose of making noise, and are characterised by the ‘standard trumpet’ sounds that can be heard here. Some other brands do different things with the air to make different noises, but this is not to be confused with the fluttering noise. Our own whistling trumpet’ is one e