compressor surge/wastegate chatter?????? weird

[audi-a6]

a weird sound from my turbo's.......... a6 2.7t (s4 engine)


hard to describe, but you know when you ease of the gas the boost dump's back in to the compressor(coz i got after-market dv's) and it should give like a "chatter" sound, well mine doesn't, well it will do it once now and again, but mainly does the same kind of sound but not "chatter" more like a constant tone (if you know what i mean) if i go on full boost, it just dumps all to atmosphere, i don't mind the waste-gate sound, i actually like it, it just don't sound like normal chatter (have owned lots of turbo cars, so i know what its suppose to sound like)

any ideas?????????

 

[Oranoco]

You shouldn't be hearing any chatter at all on your car. Wastegates also don't chatter, pet hat of mine when I hear it called that. lol

If you have recirculating dump valves you should be virtually silent if you are running an open filter a small amount of dump could be audible, if you have atmospheric dump valves then you should get a very audible "PTshhh" sound. If you are getting chatter at all then it would indicate the preload on the spring in the DV is too high.

 

[audi-a6]

i know what you mean, "each to their own" but i like it, would like it even more if it done it properly, yes the pre-load is high, i deliberately done that for the wastegate sound lol

but like's and dis-like's aside, why is it making that sound and not the proper "compressor surge" sound?

 

[Broken Byzan]

The reason it's not done is the KKK turbos have thin shafts and stall can snap them like carrots. If you really want it, pull the vacuum pipes from the DVs, No problems with not getting stall sound then.

 

[audi-a6]

know what your saying, tried that lol, still the same constant tone, ie "tchoooooooooooooo" instead of "tchoo tchoo tchoo" (sorry, thats the best way i can describe the sound)
lol

 

[<tuffty/>]

Oh dear....

<tuffty/>

 

[Broken Byzan]

know what your saying, tried that lol, still the same constant tone, ie "tchoooooooooooooo" instead of "tchoo tchoo tchoo" (sorry, thats the best way i can describe the sound)
lol

Well if it's not doing it sans vacuum pipes, it's not going to do it at all.

Maybe map it and get more boost

 

[audi-a6]

Oh dear....

<tuffty/>

what! lol

 

[audi-a6]

Well if it's not doing it sans vacuum pipes, it's not going to do it at all.

Maybe map it and get more boost

mmmmmmm, already mapped to 1.2 bar

 

[jcb]

did I stumble onto an Impreza forum?!....

 

[aragorn]

Its the length of the intake pipework on the S4 and the Y-pipe that muffles it into a constant noise.

 

[audi-a6]

Its the length of the intake pipework on the S4 and the Y-pipe that muffles it into a constant noise.

thats what i thought, but its weird why it does the "chatter" sound on average, once per drive.............

 

[audi-a6]

did I stumble onto an Impreza forum?!....

how rude!

 

[aragorn]

Maybe just the timing of the air pulses now and again occur such that you get the precise sound.

Most cars have one turbo and a fairly short hose from the compressor to the air filter.

The S4 motor has the turbo mounted down the back of the engine, and the hose runs the length of the cylinder block, up the side of the block/heads and joins the Y pipe, thru the Y and connecting hose into the MAF before finally reaching the airbox.

The Y pipe joining the two streams together will mean any sounds merge together.

The more critical point here is that the shaft in these KKK turbos is tiny, 7mm thru the bearing then necking down to 4mm where it attaches to the compressor. They really dont take well to the shock loadings from high boost and compressor stall, which is why the car is equipped with DV's in the first place.

The shaft in a T3 for instance is 10mm thru the journal and 6.35mm at the stem where it necks down. The T25 shafts are similar if a little smaller, but still MUCH bigger than the tiny thing in your turbos.

Given the rediculous amount of work involved if the turbos fail on these cars, i'd would be wise to treat them as kindly as you can.

 

[audi-a6]

So I might just put the oe valves back on then lol

 

[Oranoco]

Probably for the best.

And everything Aragorn said above doesn't start to cover the additional problems of messed up fueling