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colVR4
09-08-2006, 06:35 PM
When running my car at 1+ bar (about 1.00 to 1.05) I sometimes get a fluttering sound from the turbos. It ususally happens when I don't have it on WOT but it is still spooling up quickly and then lift of the gas suddenly.

It reminds me of the old group-b rally cars :leer: but what is causing it? I have read some other threads on the subject that say it is the BOV having insufficient boost to work properly. Will it cause any long term damage?

If I need to fix it, what do I need to get?

All answers gratefully received. :thumbsup:

colVR4
09-08-2006, 06:42 PM
A bit like this

http://video.google.co.uk/videoplay?docid=1876888814667202488&sourceid=zeitgeist

or this

http://video.google.co.uk/videoplay?docid=8826265081370207991

Free kleenex provided.... dribble!!

The Vee
09-08-2006, 08:05 PM
Havn't listened to your links but from your description, sounds like dump valve no worky proper like. Check vacuum hose to it first of all.

bradc
10-08-2006, 01:41 AM
Yeah I'd check the BOV too. If you still have the stock one, I'd get it replaced.

Kieran
10-08-2006, 08:10 AM
That 'fluttering' sound is usually the compressor blades in your turbo 'chopping' the air charge as you come off throttle (turbo stalling)- and this is usually because the BOV isn't working correctly - can you adjust the spring tension so that it opens sooner?

I seem to remember you had a Forge BOV??... you can get various colour springs (that have different tension and therefore opening pressures)... is your spring too stiff?

colVR4
10-08-2006, 09:07 AM
I bought a replacement aluminium recirc valve. I have done some more experimenting and I have found that it actually happens when I put on full boost and almost immediately life off the throttle slightly.

This means that the BOV doesn't open, but there is a decrease in pressure that the turbo is producing as opposed to the increased pressure past the turbo that it has just created, making the chopping sound. I can now even recreate it. Sounds sooo cool. I just want to make sure that I am not going to damage anything though.

colVR4
10-08-2006, 01:31 PM
More info

"The “flutter” noise reported by many excited enthusiasts may sound good but is actually very unhealthy for the turbo. The “flutter” occurs when upon shutting the throttle, air caught between the free-spinning turbo and the shut throttle. The consequent back pressure forces the air back through the turbine blades. This process, more commonly called “cavitation” places enormous loads on the turbo and can lead to premature wear of the turbo bearings and other load-bearing components. The cavitation or “flutter” can be fixed by either fitting a blow-off valve onto a system that hasn’t got one, or making sure the blow-off valve is matched to the output of the turbo and is not working outside its flow capacity and ensuring the blow-off valve is set up correctly."

I am going to see if I can get an EVO recirc valve and try it with that. I am not sure that the cheap aftermarket BOV that I have can cope with the flow.

Kieran
10-08-2006, 04:34 PM
I think it's more a case that you need a BOV that's more sensitive to pressure changes, so that it will open earlier. It sounds like it's working okay when you step off the throttle completely? If it was being overwhelmed by the amount of air, the turbos would still be stalling when you snapped off the throttle, even when the valve would be at fully open.

That make sense anyone?:undecided

colVR4
10-08-2006, 07:37 PM
Good point. I think that you may be right. I am currently pricing up a Forge/Bailey EVO closed loop valve. They do cost a bit though!!

bradc
10-08-2006, 08:39 PM
Yeah I'm with Kieran, I think it just needs a little bit of adjusting and it will be fine.