[urq] Wastegate "Chirp" is not a myth? So say the boys from UK and CAN

Sat Sep 15 17:15:27 PDT 2012

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

-----Original Message-----
From: Martin Pajak <martin at quattro.ca>
To: 'Scott Justusson' <qshipq at aol.com>; urq <urq at audifans.com>
Sent: Sat, Sep 15, 2012 4:25 pm
Subject: RE: [urq] Wastegate "Chirp" is *not* a myth?  So say the boys from UK and CAN

So what is then, wastegate flutter or compressor stall?  As per both of your responces on this matter.  
Oh wait, you just conveniently erased it from the bottom.. ;)  Not to worry, I added it back in for reference.
Can you make up your mind finally?  That coffee is not working....

Regards
Martin, chirping and fluttering apparently, must be getting old

From: Scott Justusson [mailto:qshipq at aol.com] 
Sent: 15-Sep-12 11:54
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

I guess this topic should have been on the trivia contest at urq25!  I say 'yuk' when I hear nonsense about turbo theory and operation.  You or the laddie across the pond are welcome to write up a rebuttal to *any* accepted tribute to this phenomenon.  I look forward to the Wiki correctlon too!  Use the video I referenced, but I'll warn you it won't help!  It's so easy to test this phenom without any pizzo(tm) electronic sensors, it becomes nothing more than perpetuating a myth.

Martin, the BOV or BPV could be 200mm, and compressor stall will still be measurable, and it's also audible in both your vids.  If this was indeed a WG phenom, then you could change the sound by WG variables, boost profile, WGFV application, wastegate size, wastegate exit, backpressure, etc.  Amazing when all those variables change, remove a bypass valve, and the compressor stall will still be present and audible.  Try putting a sound/heat shield on the WG, and make the same run....

Martin, you couldn't have this more wrong.  Come on out to Steamboat, we can show you compressor stall in stock Scars (because of altitude and constant tire load of low cf).  The videos you present on a closed test track, could even look better! ;)

I hope you and the esteemed gent from the UK carry this on intensely, so we can isolate the two dissenters on  the *only* forum on the net that gives the impression that this wastegate chatter myth, may be in fact:  True?!  

Carry on...  Please!   My coffee is tasting better with some chuckles this morning!

Scott "chipin' away in his junk urq's

-----Original Message-----
From: Martin Pajak <martin at quattro.ca>
To: 'Scott Justusson' <qshipq at aol.com>; urq <urq at audifans.com>
Sent: Sat, Sep 15, 2012 10:26 am
Subject: RE: [urq] Wastegate "Chirp"

I guess you can't read either, really Scott??  I have a 50mm Tial BOV
In my vid it is not from behind, but side.

Yuk is a word I would use when looking at your old blue '83..  ;)
It was for sale again not long ago.  Poor thing... someone should just put it out of its misery.

Good luck with this thread, I'll just go out an drive my car, for real.

Regards
Martin

From: Scott Justusson [mailto:qshipq at aol.com] 
Sent: 15-Sep-12 10:39
To: martin at quattro.ca; urq at audifans.com
Subject: Re: [urq] Wastegate "Chirp" on Rally, SCCA and IMSA Race Cars

Yuk again. Your vid shows compressor stall too. Add more bypass valves, you can make it go away, take the bypass valve out, you can increase the stall sound. What most don't realize is that pressure spike under load is *massive*, more than a 1in, 2in, and even 3in bypass valve can dump fast enough to prevent some stall when the throttle slams shut. I've measured peak spikes on a k2610vt in the 70-100psi range. That's gonna make a lotta noise if you then take a 650hp S1 with a monster turbo, and slam the throttle shut as it's ramping up, under load. 

Look at any groupB rally vid. You can never hear the sound from behind the car, where the WG dumps, you ALWAYS hear it as the car comes at you. That's because it's happening at the compressor side, not the exhaust. Take all 10minutes of that video below, and point me to WG 'chirp' or WG flutter. 

You guys are making my coffee taste funny, but appreciate the chuckles

Really Martin?! 

SJ

From: Scott Justusson [mailto:qshipq at aol.com] 
Sent: 15-Sep-12 10:00
To: martin at quattro.ca; urq at audifans.com
Subject: Re: [urq] Wastegate "Chirp" on Rally, SCCA and IMSA Race Cars

Yuk. Wastegate 'flutter' is not the 'chirp' being referred to. Wastegate flutter (an open throttle pheonomenon) can't be heard on any rally car, even if you left the WG exhaust open to atmo. Go :40sec into this vid, then tray again at 5:50-6:10... Better yet, watch all 10 minutes and find an instance of WG chatter, I sure couldn't do it. But I'm sure you guys know better.....
https://www.youtube.com/watch?v=ejIhA2UhfNA

Come on boys, I mean... Really!?!?

Scott 'chipin' J

-----Original Message-----
From: Martin Pajak <martin at quattro.ca>
To: phil <phil at isham-research.co.uk>; urq <urq at audifans.com>
Sent: Sat, Sep 15, 2012 8:26 am
Subject: Re: [urq] Wastegate "Chirp" on Rally, SCCA and IMSA Race Cars

Hi Phil,

Must be something to it, I have a stock wastegate, a big 50mm Tial dump
valve (setup with proper spring for nice pssssh, it is open at idle).
3071r turbo with mushroom HKS filter.  Yet I still get the chirping sound
from the exhaust side of the engine, in addition to the whoosh from the dump
(so I do not think it is a stall).  You can sort of hear it here, but it is
much better in real life.
http://www.youtube.com/watch?v=qIyj8El8jkA

Cheers
Martin Pajak

http://www.quattro.ca 

1982 Audi Ur-quattro, SQ project
1983 Audi 80 quattro, Euro 2-Tür
1983 Audi Ur-quattro, Stock Helios Blue
1984 Audi Ur-quattro, 20vt with 6-speed
1993 Audi 90 CS quattro, 2.5 TDI with 6-speed
1993 Audi 80 quattro Avant, 2.5 TDI with 6-speed

-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf
Of Phil Payne
Sent: 15-Sep-12 03:56
To: 'Scott Justusson'; ub3ratl4sf00 at gmail.com; koenigj at comcast.net;
urq at audifans.com
Subject: Re: [urq] Wastegate "Chirp" on Rally, SCCA and IMSA Race Cars

Well, here we go again.  I once had a long history of disagreeing with
Scott.

The chatter that I hear is almost always wastegate.  I've had Snap-off
piezo-electric microphones all over the engine bay and that's where it's
coming from.

However, I do very much agree with the problems that turbo stall can cause
on turbos - especially the K24.  What exacerbates this problem (in the UK)
is that the dominant turbo rebuilder (http://www.aet-turbos.co.uk/ - good
guys) won't accept a turbo with a broken shaft as an exchange item.  Having
seen them strip one, I can understand why.

I also agree with the comments about bypass valve capacity.

I've got other reservations.  Over here, Bailey is a dominant supplier of
bypass (and blow-off) valves, but their product has a non-linear opening
characteristic that I believe results in some back pressure before it opens.
The unit Audi fitted to the ur-quattro 20V (035 145 710) has a much smoother
opening profile but - as Scott implies - does have a restricted capacity.

Nevertheless - I do agree that fitting such a valve increases turbo lifetime
and is in general a very good, cheap and easily reversed modification.  For
most untweaked 10Vs I recommend the 20V part (number above) but do make sure
that you don't impede airflow over the turbo and exhaust manifold when you
fit it.

-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf
Of Scott Justusson
Sent: 15 September 2012 04:22
To: ub3ratl4sf00 at gmail.com; koenigj at comcast.net; urq at audifans.com
Subject: Re: [urq] Wastegate "Chirp" on Rally, SCCA and IMSA Race Cars

Except all WRC and ProRally urq's chattered, from day 1, btwitnessedt.
Read: Only the later cars had the recirc setup.  In the early cars and even
the reference below, it was not 'wastegate' chatter it was always compressor
stall from a turbo spooling up and the throttle slamming shut.  There were
no bypass valves in the early cars, so with big turbos, you heard the
compressor stall.  On Buffum's drives back in the early 80's, you would hear
that chirping 5 miinutes before you even saw the car.

We actually get a lot of it quite noticeable at Steamboat with the 20vt
k24's.  When I discussed it with Ned Ritchie years ago, we figured it was
the turbo working beyond the ability of the bypass valve to dump at altitude
(with tires on ice spinning up under load), that caused turbo stall.  If you
really like that noise, put a cone filter in place of the airbox, you will
hear compressor stall during street driving.  Or put a restrictor in the
bypass valve, or plug the bypass valve all together.

All that said, it's not a healthy noise for turbo longevity, especially on a
k24, btblewthat up at steamboat in my 10vt k24 urq.  That small shaft can't
take the thrust load of the stall.

Cheers, hey Roland, and my .02

Scott J
chirping 20vt 4kq cone filter
84 urq
83 urq