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

[Scott Justusson]

 No one will forget the sounds of Steamboat that year Dave!  Between Chad in your car, and my drive in Pederson's green garbage can, wildlife in the area stayed very clear of the snorting, farting beasts.  Alas, at 7600feet a lot of compressor stall can be heard year after year, with even the small k24 turbos, btdt with my rides, and my drives of your other 'two' turbo cars you sent into that theatre.

I stick this one out, because this very phenomenon properly identified, really makes tracking Audisport's approaches to the resulting issues this presented, much more interesting.  And, they use much of what they learned back in groupB, in their racing efforts today.  One of the biggest benefits this created, was the massive turbo development effort for 'advanced' wastegate control.  Those WRC rally cars, didn't really have anything more than wastegate springs.  Add in the electro-hydraulic clutch switch, work of art IM's, the crazy dual EM's; culminating in the actual insertion of a fuel injector in the EM for the Hillclimb (Pikes Peak etc) cars.  Watch a S1 without this mod leave the line, they are damn slow out of the hole, but once that turbo boils, they become unruly beasts.

We can thank the FIA 1.4 turbo equivalency rules for making Audisport work hard for those wins in small displacement, massive turbo engines.  And this GroupB obsession for power Audisport focused on in the S1 Evo, pushed the best talent A.S. could buy, to the very limits of their skills.  I spoke directly with Blomqvist on this for quite a while at Maine 99, the stories he told of the rides in these Beasts were riveting.  And he admitted fully, only Walter could really make the Shorty's dance.  He always opted for the LWB quattros whenever given the choice.

As I read Claus clamp a massive turbo on a 2.2, not much has changed.  It's all about the exhaust energy on the one side.  On the other is what you do with all that built up pressure when you finally get the turbo up to boil.  Audisport kept the BOV/BPV out of the cars intentionally, keeping that pressure spike bouncing in the cold side tract, for the next throttle opening.  Which is why you see doubled up pipe bridges between every cold side hose.  And even today, many of these massive HP cars, are bested at the track with much smaller turbos/hp, because the torque and regains of on-line speed, is not an easy equation to get right.   BTbuiltT, BTdroveT

All this backs up to the noises in these vids.  If you believe the myth that it's a wastegate phenomenon, it's almost impossible to understand Audisport's develepment history.  Me, I doubt any Audisport GroupB car worked wastegates much at all.  That thing is simply slammed shut over 80% of the rpm band, and probably more.  Because as Claus and many others found out, once that WG opens, 'control' with 2.1/2.2l of displacement, is an oxymoron with the best of electronic WG control.

Back to those compressor stall trumpets barking in the woods 10 minutes before the beast snarls by in an instant...  That's where it all started, it's not the wastegate gents....

Cheers

Scott J
84 urq
83 urq




 

 

-----Original Message-----
From: djdawson2 <djdawson2 at aol.com>
To: qshipq <qshipq at aol.com>; urq <urq at audifans.com>
Sent: Sat, Sep 15, 2012 10:45 pm
Subject: Re: [urq] Wastegate "Chirp" is *not* a myth? So say the boys from UK and CAN


Guys,

I've had plenty of reasons to debate Scotty J in the past, and there's been more than a few times that we didn't see eye to eye.

But the thought that this is wastegate chirp?  Seriously?

Think about this logically for a second.  The WG only opens when the pressure in the exhaust manifold - between the head and the turbine - surpasses the WG spring's ability to hold it shut.  This is typically wide open throttle, or close to it.  Watch any of these videos, and it seems like it should be more than obvious that this is a lift-throttle phenomenon... not wide open.

My 930's WG noise is very obvious, and couldn't possibly be confused with compressor stall.  The only thing is does is get plenty loud when it begins to open, as it vents to atmosphere through a small muffler.  It continues to get louder as the rpm's build... sounds quite a lot like an exhaust leak on a NA engine.

When trying to fully understand the compressor surge I was experiencing using a GT3076R on my 2.2 20v, I too locked my WG shut by placing a solid object inside the WG cover such that it could not possibly open.  I then tested VERY carefully to determine if my WG control had anything to do with my perceived surge issue.  It did not.  But more important to this discussion, my compressor still made that beautiful chirping sound as I lifted... no WG behavior was even possible.

BTW, worth noting that my intake consisted of a very large K&N inlet, flowing through 4 inch plumbing, through a "flow straightener" (suggested by the original UrS intake design), and into a Porsche 928 MAF.  With this intake, all of this compressor noise was very noticeable, quite loud in fact... ask anyone who listened to Chad Clark scream that car around the Steamboat track.

As I progressed with this engine, I ditched the little OE Bosch BPV with a billet unit using 1 1/4 inch plumbing.  This did reduce the chirp, but did not entirely eliminate it.

Long story short... I can't imagine how you guys could possibly think this is WG noise.  The pressure spike after the throttle plate slaps shut ought to be enough evidence to convince anyone.  I have not measured that spike, but every time I blew pressure hoses, it was when I lifted to shift gears.

Anyway... best of luck on this discussion.

Dave