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

[Scott Justusson]

 Propogating the biggest myth to the idea of wastegate chatter.  Even Wiki references this very myth.  Several problems (regardless of where you put microphones) with the very theory it's wastegate.  Take that same k27 WRC turbo, with the very same wastegate, and add 4 stock bosch 701N/710 bypass valves, the turbo won't compressor stall, so no wastegate chatter under all the same conditions and throttle positions.  I claim this is exactly a valid test, because I've done it. All wastegate variables/boost/turbo size stay the same, vary only the count of the bypass valve, you can sount-tune the amount of compressor stall/chirp.

You can make compressor stall by removing the bypass valve on a k24, so it's not the 'size of the turbo' , size or the wastegate, the wastegate dump to downpipe or separate exhaust (ala rally cars).  You can hear compessor surge better by removing the airbox.  It's the pressure side causing the problem and the noise.  

If you want to claim it's wastegate 'chatter' then the chatter should 'also' happen at a fixed throttle opening and vary with wastegate valve size, and spring pressure.  If you look at any video, or in my case stand in the woods listening to Buffums cars for many hours over the years working rallye's, you will realize quickly it's a *lift* throttle phenomenon only, as in closed plate.  Audi didn't use bypass valves mostly because with the very large intercoolers, they intentionally kept the pressure wave internal to the IC for the next open throttle event.

Audi addressed this in the later 10vt 200 by putting a throttle-shut delay valve on the cable cam.  This helped reduce the pressure wave spike that went back to the compressor wheel, and this was a good upgrade back in the day, btdt.  With the 200 20vt came the addition of the bypass valve, which became all the rage, because you can tune the surge to be a controlled fart.  

Really really tough to argue the wastegate chatter myth is indeed true, whatever one thinks they heard or measured.

Scott J
always a smile for at least one conspiracy theorist across the pond

 

 

-----Original Message-----
From: Phil Payne <phil at isham-research.co.uk>
To: 'Scott Justusson' <qshipq at aol.com>; ub3ratl4sf00 <ub3ratl4sf00 at gmail.com>; koenigj <koenigj at comcast.net>; urq <urq at audifans.com>
Sent: Sat, Sep 15, 2012 2:56 am
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.