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Supercharger makes a Poof sound when engine turned off ??

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2010 Shelby GT500

Can anyone confirm that an Air Release sound coming out of the Air Filter when the engine is turned off each time is NORMAL? Not heard while in the car with the hood down, but with Hood up and standing near the engine. It happens on every engine shut down.
-- A POOF like sound escaping from the Air Filter
Again - My Local Ford Dealer Mechanic informed me that this is a normal occurrence with the Supercharger. And since I have an Aftermarket K&N Air Filter, it is even louder.

Was told by another Senior Service ADVISOR - that K&N air filters are not very good and that they allow more dirt to enter the fuel system and destroys vehicles.

Would like to know thoughts on K&N air filters and if this Air Poofing sound is in fact NORMAL.


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  • Well, this is every time the engine is shut down. Not noticeable from inside the car with the hood down.

Just a Pssshhhhhh. sound - like an air brake being released. Definitely not an explosion thank god.

Can you check your Shelby? Hood up and standing in front near engine. ( I guess if you lean out the Drivers window, you could hear it too)

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  • 3 weeks later...

These cars have vacuum-powered brakes that store vacuum while the engine is running. That vacuum is developed right behind the throttle butterfly and before the supercharger. There is a check valve on the brake booster to hold that vacuum in case of power loss. But the line from the booster and the throttle body area has a vacuum in it. When the engine is shut off, the throttle blades close and that small amount of vacuum built up behind the blades vents into the intake tube, probably sounds like its coming out of the air filter. This is quite normal.


As to K&N filters, that's all I have ever used, and have currently in all five of my vehicles. They work great and last essentially forever. Your service advisor wants to sell you a new air filter every time you stop in. Ignore them.

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