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the 'fluttering' that i think you are describing is called 'compressor surge'. it happens when the bov it sprung too tight or when you don't have a bov (ie not a skyline).

when the throttle body closes (like taking the foot off the accelerator), the comressed air hits and reflects back in the direction it came. in a skyline the bov would open and air would pass out through this making a 'ppsssssshhhhhhhhhh' sound. if no bov, then the air goes back through the intercooler and passes through the compressor side of the turbo in the opposite direction to the spinning blades and as mentioned by obseshn this 'chops' the air up making a fluttering noise. as you can imagine it ain't good for the turbocharger even if it sounds good.

hope that helped.

Waz.

Have a friend who ran a turbo for quite a while with no BOV and it was still fine. Unsure about my car but it's making a fluttering/chattering/chopping noise so either the BOV's pretty tight or the previous owner removed it. Will have to perform a more thorough investigation but everything's in good nick!

definitely not wastegate. on closed throttle there's no air going through the engine so the wastegate opening and shutting wouldn't do much. Either the BOV fluttering or compressor surge with air reverting back through the turbine compressor blades.

This "fluttering" is also a major factor in engine stalls when comming to a stop. I was investigating stalling issues on my car a while back and did some measurements with an oscilliscope on the AFM. I've attached an image of AFM voltage with a "loose" and "tight" BOV. Note that the "tight" setting produced audible "flutter" through the AFM after a rev, and this is seen as the severe oscillations in the trace indicating reversion due to compressor surge....

phantom

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