When I get off the gas pedal under hard aceleration I hear a noise as if a fan blade is hitting something, I was told it might be a butterfly valve. Is it? What is a butterfly valve? What else could be the problem?
It is not the fan as I thought it might be.
More likely the sound of the turbo unspooling which is normal. Becomes much more noticiable when you go to an open air filter or a larger turbo.
I guess that's possible but I'm not sure this noise is normal, I wish I could explain it better or have you hear it. It is a very distinguishable noise and I'm sure yuo would know what it was as soon as you heard it. I'll try to think of a better explaination of the noise.
Thanks for your input.
Its likely what's called 'compressor slam' or 'turbo sneeze'. Basically, what Steve is describing. Its a noise made by the fast-moving air running into the deaccelerating compressor wheel. A very distinctive sound, and much louder when the stock airbox is exchanged for an open element filter system.
hmmmm, you guys are the experts, I guess I can drive it without any worries of breaking anything.
Thanks for your help, I'm a new GN owner and I'm sure many questions will follow.
Thanks Again!
I was going to post this question also. Glad I read this. Is there anyway to stop this noise. It doesn't sound real "cool". If it's the nature of the beast then so be it, but I don't like it....sounds cheap.
The stock airbox system is designed to minimize this sound. If you are running an open element air filter, replacing it with the stock airbox setup will quiet things down. Of course that'll limit your airflow, too...
During normal driving this really shouldn't be happening anyway. Only when you rapidly let off the throttle while under boost. This rapid change can in time be hard on the turbo bearings, so I would discourage anyone from making a habit of trying to cause the sound.