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If you’ve heard turbo flutter, you’ve probably thought it was the coolest thing you’ve ever heard, and if you also have a car with a turbo, you were probably wondering why yours doesn’t sound like that. Unfortunately, there’s a cost to that beautiful noise, and we’re going to go over it here, along with some other turbo noise options.
How it works:
When a turbo builds boost, it does so by spinning a turbine that sucks in air and compresses it. When you have the throttle open, this compressed air is rushing into your engine, but when you let off the throttle and the plate closes, your turbo doesn’t just stop making boost immediately because that turbine has to slow down, and now you have a plate blocking most of your boost in your intake. This pressure needs to go somewhere, and you have three options for how you manage that excess air:
Bypass Valve (BPV):
A bypass valve, or BPV, opens when it senses this pressure differential from before and after your throttle, and recirculates the pressure back to your intake. This is what turbo subarus come with from the factory. Installing an aftermarket BPV on your car does not require a tune, as all it does is put that air back into the system. You normally can’t hear this operating without an aftermarket intake, and when you do have an aftermarket intake, it sounds like this: https://www.youtube.com/shorts/RH2EP26iyB4
Blow Off Valve (BOV):
A blow off valve, or BOV activates in the same way as a BPV does, but the difference lies in where it puts the excess boost. A BOV vents that excess boost to the atmosphere. These can vent pressure faster than a BPV, but require a tune. They are also louder, and can be heard with a stock intake. The sound greatly depends on the specific model you choose, with some companies making BOVs that simulate turbo flutter, and some sounding like a louder BPV.
Neither:
If those two options aren’t for you, you technically don’t have to use either. If you choose to delete the valve, the boost will push past the turbine and out of your intake. This is the classic flutter that you hear. The high pressure air fights against the rotation of the turbine, and makes the turbine “flutter” back and forth, creating the sound. This is hard on your turbo, and reduces its lifespan. There’s no specific number for how much, so it entirely depends on the risks you want to run. It sounds like–you already know.
If you want to dive into this topic a little more, here’s a video from someone far smarter than myself: https://www.youtube.com/watch?v=BFXIgME_5UA
Cover Image from VividRacing.