[urq] Wastegate "Chirp" on Rally, SCCA and IMSA Race Cars

[Scott Justusson]

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

 

 

 

-----Original Message-----
From: Stephen Kraus <ub3ratl4sf00 at gmail.com>
To: John Koenig <koenigj at comcast.net>; urq <urq at audifans.com>
Sent: Fri, Sep 14, 2012 9:03 pm
Subject: Re: [urq] Wastegate "Chirp" on Rally, SCCA and IMSA Race Cars


For more info:
http://en.wikipedia.org/wiki/Audi_Quattro#Sport_Quattro_S1_E2

The boost pressure was recirculated into the turbo when the driver comes
off the throttle, the throttle plate closes, the extra boost pressure
recirculated back into the turbo, keeping it spooling for when the throttle
plate re-opens.

No loss of boost pressure when the driver shifts and engine resume high
speed instantly, but the brief blockage of the pressure and recirculating
air makes the turbo chatter.
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