Not the BOV noise the other one?

[Moschops]

Mine does this as i'm CLOSING the throttle, not when it's closed. If i'm accelerating in, say, 5th and ease off fairly gently (not snap it closed) then I get the HKS BOV whistle at the same time the wastegate flutters. I know the fluttering on my car is the wastegate and not the BOV as the BOV sound is of constant pitch.

My understanding of the sound you describe is the wastegate swing valve opening and closing to balance the pressure.

Could be wrong, I was once.

[ApacheX]

Originally posted by the phantom

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

so r u sayin if u put the bov on "tight", it will reduce the stalling?

[the phantom]

No, the opposite. If its tight you will get reversion as the BOV doesn't open unless you have been at full load i.e between gears at redline, or otherwise drawing a huge vacuum. For low and medium loads insufficient engine vacuum will exist to overcome the spring, rendering the BOV useless. The subsequent reversion (compressor surge) event will lead to instability as the ECU attempts to follow the wildly varying AFM voltages with your fuel map. If this happens as your comming to idle, a stall is likely to follow, particularly if your AAC valve isn't quite what it used to be, and you have a larger than stock turbo. Therefore a slack BOV will guard against reversion and allow the AFM to provide a 'smoothe' response to the ECU. This is what the traces show in my previous post.

In other words....leave it slack....even to the point of it being open at idle. As soon as you get on the power the boost will assist the spring and keep the BOV shut. The trick is to adjust it appropriatey at low/medium loads if street drivability and an extended turbo life are part of your agenda.

It is also worth mentioning that even though I have a PowerFC on my car, and swear by it, it has an inferior idle control strategy compared to a factory ECU in regard to AAC valve operation...this may be more relevant to the 'other' thread however, and is a whole other story....

[ApacheX]

ah crap, time to change the bov...again ehhe

thanks phantom

[the phantom]

I forgot to stress the assumtion that the BOV be plumbed back to the intake....

[Cool Hand Luke]

If your getting a "fluttering" sound under high boost, that is also compressor surge.. a result of a mis-matched turbo/engine combination. Read a few zoom issues ago, its power robbing and also bad for the turbo.

I admit the choo choo choo sound is unreal, when i bought my 180 the guy had the blow off valve hooked up in-correctly and didnt work at all (he had no idea it wasnt working). It runs high boost and has big piping so there was alot of air in there, and made a better sounding and far louder sounding noise than any blow off valve i've heard. Im interested to see how the turbo is now after 6 or 8 months of driving around like that running 26psi, but it cant be good for it and made it laggy as hell between shifts.

[Cubes]

Those of you with bigger turbo's and have upgraded the BOV to a larger higher flowing item, have you noticed any decrease in lag between shifts?