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ke382TG
Forums Junkie

Registered:
May 2002

Re: Blow Off Valves

Fri, 22 October 2004 01:37

Quote:

my BOV is a tial, and it sorta makes a puring fluttering sound, sorta like compressor surge. this is only when i change gear and there is none or little boost. when i back off at higher boost, say 15-20psi its more of a woosh sound. and before anyone says the fluttering is my BOV not opening causing compressor surge at low boost its definately not. the BOV opens FULLY.

Just to offer some advice (and a minor performance gain of better low boost response between gears Very Happy

if you choose to take the advice).

The Tial BOV is a sweet bit of gear and uses the common BOV design in which there is a piston inside the BOV housing. The chamber on one side of this piston has a tubular line that runs to the manifold allowing both boost and vacuum to be created in the chamber. This side of the piston also houses a spring (adjustable in pre-load).

The other side of the piston will see atmospheric pressure through to boost.

Now the only noise this type of BOV can make is that of air escaping when it opens, this is the woosh or psshhh or hiss you indicate you get at 15 - 20 psi. The fluttering noise can not be created by the BOV as to do this it would have to be opening and closing at a rapid rate or "pulsing" (think about it for a second and it will make sense). Now that you have thought about that do you see what I am saying?? In between your gear changes even after only spooling up the turbo a small amount one side of the BOV piston is seeing vacuum, the other side is seeing boost, so unless the vacuum is fluctuating a great deal then there is now way for the piston to be opening and closing at a rapid rate to cause the fluttering noise.

But this is easy to rectify and will help keep your turbo spinning a touch longer and hence less time to bring it back on boost between gear changes Very Happy

Now I don't know where you have your BOV located but I will assume it's nice and close to the throttle (no problem if it isn't but this is the ideal location). Now with a neat BOV like you have (and most others these days) it is possible to adjust the spring tension (or purchase a different spring rate) to have it set up for your particular vehicle.

The simple thing to do in order to remove this "fluttering" noise at low boost gear changes (I am 99.9% confident you can get rid of it) is to just back off some of the preload on the spring. If this is already at it's minimal preload adjustment then a slightly softer spring is in order (sounds like it is only just a tiny bit too much preload though).

The only other reason I have seen for this flutter on low boost gear changes is that some cars have had such a long line from the manifold to the BOV that the minute delay this causes in allowing the BOV to respond causes a small amount of compressor surge before the BOV is able to open.

The ideal is to have no compressor surge at all, and don't worry about the BOV "leaking" if the sping is set quite soft, it won't happen Very Happy

If you decide to have a play around with it let us know how you go, it's free performance to unleash (even if it is only a small amount Smile