[urq] Wastegate "Chirp" is *not* a myth? So says Phil from the UK

[Scott Justusson]

Excellent, so it's only the gent across the pond that believes in the myth that the sounds of compressor stall is Wastegate flutter.  So noted in the subject line above.  A 50mm BOV will chirp, as pressure differential does funny things, btdt.  I prefer two smaller adjustable BOV, one set to open with light preload just prior to the t-body, and 1 with heavy preload between the turbo and IC.  This allows a progression of the pressure dump, especially on larger turbos.

The vid you reference is a good one, I too have that and a few more VHS copies that never made the transition to DVD.  

Next time, you can first agree that the sound the OP is referring to is indeed compressor stall, whatever sounds your BOV makes.  My beer tastes much better now.

Thanks for clearing up your understanding Martin!

Cheers

Scott J



-----Original Message-----
From: Martin Pajak <martin at quattro.ca>
To: 'Scott Justusson' <qshipq at aol.com>; urq <urq at audifans.com>
Sent: Sun, Sep 16, 2012 5:25 pm
Subject: RE: [urq] Wastegate "Chirp" is *not* a myth?  So say the boys from UK and CAN


Scott,
 
If you go through my emails I NEVER said my issue is NOT a compressor stall, simply that I have a 50mm BOV and I have (what I hear as) chirping.
I have seen many many hours of rally footage, so I am very much aware of what the chirp sounds like, the best one has to be 
http://www.youtube.com/watch?v=NtWsn8k8Rcw
Nothing but pure sound all the way from A1 to S1.  I have a nice rip of the original VHS, much better qulity than the youtube version1.5gigs of pure sex
My chirping might not be as loud as an S1 car hence my videos are poor reflection of real life, but it is there.
With a nice and large BOV compressor stall did not make sense to me, especially that it is located 2" away from the throttle and acts very fast, woosh comes at the same time as the chirp.
 
What got me is that one minute you said WG flutter, and the next compressor stall, very confusing indeed.
My initial responce to Phil was just an observation, but somehow got you all defensive.
 
When the hell did I say rally cars have wastegate flutter?  I can't show it to you if I don't believe in it.
 
That coffee starting to kick in yet??
 
Cheers
Martin 



From: Scott Justusson [mailto:qshipq at aol.com] 
Sent: 15-Sep-12 20:15
To: martin at quattro.ca; urq at audifans.com
Subject: Re: [urq] Wastegate "Chirp" is *not* a myth? So say the boys from UK and CAN



There was a time when I too thought compressor stall was wastegate flutter.  I found Ned was correct during a great beer discussion on this very topic many years ago.   On the suggestion of a well respected turbo builder several years ago, I clamped a wastegate shut, and found the chirp (as heard in the group B vid, and your vids) was compressor stall, nothing else.  Then I took a 470whp quattro and actually tested various 'leaks' (BOV, BPV, and respective boost references to the WG/IM), and found everything in your video, and everything in the group B vids, and attributed the chirps to compressor stall.  Where I got misled drinking the "myth Koolaid" many years back, is that *a compressor stall event does not require a fully 'closed' throttle*.  In  fact, the bigger the turbo and/or the smaller the engine, only a small amount of 'lift throttle' creates the stall when under load.  

 When I tested this phenom,  I used a Fluke meter with peak and hold memory pressure guages mounted before and after the intercooler, and measured some pretty impressive boost spikes.  On the 470hp quattro, I also tested various preloads of the largest adjustable HKS non-recirc BPV.  With small changes in preload, I could tune the compressor stall events, the amount of boost spike, and the resulting sounds.  Adding in 2 HKS BPV, I still measured compressor stall pressure spikes of over 2:1 (PR:Boost spike) ratios on that engine

I'm sorry if I cut something off that you somehow think 'helped' you.  I was going to start down the road of the difference between BOV and a BPV, but decided your videos both clearly demonstrate compressor stall events.  Reprased:  "Your videos also ("too" - as along with the groupB vid) shows clearly compressor stall events."  Not "in addition to wastegate flutter", just compressor stall events.

Sorry if it wasn't clear enough for you.  If you would like to point me to wastegate flutter events in the groupB vid or yours, please do reference the video and a time base control for me to listen for them.  I assure you, I have the right video and audio equipment to decipher something even close.

Or, we could just look to the group B vid, ask Roland if this is what he was speaking to, and call "compressor stall" what made those cool sounds.  It's unclear to me that you agree the 10min vid I referenced clearly demonstrates compressor stall events by the dozens.  If you agree, then we can move on to your specific application and claims on your car, starting with the difference between a BOV and BPV functions, respectively

Thanks for hangin in there Martin, I'm sure you and Phil can clarify your claims better than you have.

Best Chirps from the Chicago stall

Scott J