Recognizing the Audi Sport Quattro S1's sounds

I'd just like to confirm my guesses of the sounds an Audi Sport Quattro S1. If you watch any videos featuring Quattros rallying, such as http://www.youtube.com/watch?v=mykztO1zeUU (the S1 is the one with the massive body kit) you will notice a few sounds

- When a Sport Quattro S1 (S1 for short) shifts, you hear something like gears grinding against each other. Is this due to the straight-cut sequential gearbox? Or is it actually the sound of the wastegate from the turbo? This sound is not present when a normal Sport Quattro shifts, so I doubt it's the turbo. If it's the gears grinding, it can't be good for the gearbox right?

- When the S1 shifts, there is significant backfire (from the exhaust). I know this is because there is unburnt fuel leaving the engine and burns in the hot gases. However, is the reason for this unburnt fuel because of the anti-lag system? I read on Wikipedia that 1 type of anti-lag system is to burn the fuel incompletely in the engine then expel it, so it still has enough enthalpy to drive the turbocharger even at low engine-revs (which makes sense since when you shift up, the engine revs drop). Or is this because the fuel injection is timed badly?

 

You don't mean the bird chirping sound at the 5:00 and 5:45 mark?
ACF Tahkovuori 2011 by JTmedia - YouTube

That's the turbo. And if I can afford, that's the place I'm going to be next winter

 

if it's a chirping or "whoosh" sound then that's the blow off valve.

as for straight-cut gears, u will hear an unmistakable, annoying whine.

also, rally cars often stay in the lower gears as they slide through turns. u'll often hear them bouncing off the rev limiter. racing is all about staying in your power band, at all times.

 

No blow-off valve was used in those, the chirping sound is from the air rushing in the turbo. I just cannot explain it right now, I need to find the source material so I could translate and then explain it

That's the problem when I'm not native english speaker. Hard to explain something, when I can't do it properly even in Finnish

 

ahhh, u'r probably talking about the turbo spooling sound. sounds like a jet engine sucking in air.

blow off valves will only go off when u are currently in boost and then let off the throttle, so they'll be in between shifts.

edit: http://youtu.be/qzNdJ3LPu4Y

from 0:01 - 0:07, u'll hear the turbo spooling or building up boost. at the 0:07 - 0:08, u hear the blow off valve going crazy when he lets off the throttle.

 

OK thanks guys, so the chirping is due to the turbo? Why is this only present in the Sport Quattro S1 and not the Quattro or Sport Quattro? They all have turbochargers.

Also the backfire, is that due to the anti-lag system or just poorly-timed fuel injection?

 

A hiss is spooling of the turbo.

The chirp when shifting is air hitting the wall that is a closed throttle body and being circulated back to the intake system. This can be achieved in a few ways:

-back to the intake unaltered (very inefficient)
-back to the intake through a CBV or Compressor Bypass Valve (very efficient) (PS: Blow off valve is a ricer term for CBV so I dont acknowledge it as a term, sorry)
-out to the atmosphere (VERY VERY inefficient!)

 

Because those engines had no wastegate/blow-off/dump valve the air is forced backwards and that causes the turbo chirp like a bird. Something like that, I just cannot find the hard evidence again...

That video I posted was regular urQuattro with "some" tuning and paintjob, made to look like the real thing. You'll notice the back windows are bigger than the shortened rally version had.

Also seen/heard in the "road" cars
Audi IMSA GTO: Audi 90 IMSA GTO sound - YouTube
Secrets of speed part3 - YouTube
Audi IMSA-Trans AM Racing In The USA 1988 1989 VHSRiP - YouTube most of engine sounds are covered by music though.

 

Thanks guys, so that chirp is the air going from the turbo back into the turbo basically?

Also anyone know why you don't usually hear this in the Quattro or Sport Quattro, just the S1?

 

That's what I've been told and I've read.
I'd say it depends on engine tune level. Bigger the power output, more audible chirp