roboldham Posted February 27, 2003 Share Posted February 27, 2003 Hi folks Posted about this a few weeks back - still not got to the bottom of it. I am gonna get Leon to have a butchers / listen but thought I'd try my luck here again first. Basically, when coming off a sustained and heavy boost on the second turbo - dropping down past 5K revs, in 4th mainly, but also in 3rd to a lesser degree I get a really unpleasant engine noise. It grows from a quite rasping noise, grows in volume to something not ulkike a WWWII spitfire engine sound - its in synch with the engine revs, and quitens off again after a few seconds as I let off the gas. If I push the boost back up again (throttle) (have only risked this a couple of times) it increases slighty then sometimes 'pops' - like a vent shutting. It seems to be the left side of the engine (as you look fwd) - and kind of sounds like plastic fan catching on metal, or a diaphragm flapping, or even just a piece of plastic flapping against someting - but its not speed dependent - but revs. Thought about dumpvalves, cams, belts all sorts - cant place it and cant immediately see anything loose (although I cant really get a proper look) Odd I know - and REALLY bugging me now - enough to stay off the second blower for serious time. R Link to comment Share on other sites More sharing options...
Ian C Posted February 28, 2003 Share Posted February 28, 2003 Aeons ago I got a really loud screeching wail from my MkIII when I hit high boost high revs. I thought the turbo was on the way out, but I wasn't going to get it looked at until I got the rearmost manifold stud recoiled - the threads had stripped and the exhaust manifold was blowing. Turns out, it was the exhaust gasket oscillating in a reed-style manner - when the exhaust gas was flowing hard and fast enough it would leak past the gasket and vibrate it. Anyway - sound a similar pressure related thing. If it's when you come off a high boost moment, it might well be the intake side being pressurised when the throttle closes and leaking past something, causing the reed effect. Perhaps your BOV is not opening and it's the turbo's stalling under the sudden back pressure? A start for you, anyway -Ian Link to comment Share on other sites More sharing options...
Alex Posted February 28, 2003 Share Posted February 28, 2003 Isn't it just caused by a sort of 2nd turbo stall... Link to comment Share on other sites More sharing options...
roboldham Posted February 28, 2003 Author Share Posted February 28, 2003 These sound feasbile - BOV could be the culprit. What pressure is the standard JSPEC one rated to? R Link to comment Share on other sites More sharing options...
Alex Posted February 28, 2003 Share Posted February 28, 2003 Think its actually VSV related or something like that.... 'cause it happened on my stock bov and my HKS SSQV Link to comment Share on other sites More sharing options...
roboldham Posted March 1, 2003 Author Share Posted March 1, 2003 VSV . . . eh, elaborate dear scribe. please! R Link to comment Share on other sites More sharing options...
Alex Posted March 1, 2003 Share Posted March 1, 2003 Erm can't, don't have the technical ability/understanding, sorry. But in laymens terms I think it gets itself (the sequential system) in a knot when slowing down gently with the throttle still gently applied. Link to comment Share on other sites More sharing options...
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