Turbo Noise

[ub7rm]

Hello,

Stupid question perhaps but I was driving along the other day with the window down and could hear the turbo spinning up merily as I accelerated, coming off a roundabout I booted it and realised that the turbo was spinning up, then down then up again a few time till I hit about 5k rpm, changed up and the same thing.  I was wondering if this was normal, I thought it just spinned up constantly till you eased off the gas? 

Your thoughts appreciated.

[topher]

are you losing power when you hear the turbo back off ?

[ub7rm]

No pulls solidly all the time, haven't had the car all that long.  Certainly cant complain at performance but then I don't know what is normal for this car.  Though it accelerates with gusto there is no kick throwing you into the back of the seat but from what I've heard here its a low pressure turbo and wont have a dramatic effect anyway?  Forgot to say that its a petrol, AUM engine I believe.

Thanks

[ub7rm]

Update:

I think I may be loosing power, acceleration seems flater than it used to be.  No warning lamps.  Any ideas people?  Help!

thanks,
Ron

[GolfGL]

Have a look at the common problems section at the top.

[New Duncan]

"No pulls solidly all the time, haven't had the car all that long.  Certainly cant complain at performance but then I don't know what is normal for this car.  Though it accelerates with gusto there is no kick throwing you into the back of the seat but from what I've heard here its a low pressure turbo and wont have a dramatic effect anyway?  Forgot to say that its a petrol, AUM engine I believe "

Hey, how many 000's has your Mk4 turbo done, is she a 3 door ? Is the engine guard around the sump area in the correct position. This stops air turbulence the engine bay, that can change the sound when proper motoring ? Check ?

This is a good sign, pulls solidly all the time, Gusto is fine for the 150 unit.  You  Can Obtain Significantly More - Yep, soft turbo, not blown, but induction pressure is adjustable, according to my Audi/BM guru.

You won't get the old style twin Garratt air turbo feel, but then you get very little lag, since it's progressive, and more control of the front wheels.

On tick over you should just hear the bank of 4 extra inlet valves operating through the turbo chamber. These valves are heard above, (a different pitch than) the other 8 inlet valves and opposite the 8 other exhaust valves. the engine should be very quiet. When accelerating the spinning is fine, as long as you don't hear it whistling higher than your increases and decreases in revs.  As you drop the throttle, turbo goes off, and you may get some jitter from the overhead cam on the inlet site. Get the best Fully synthetic all in that engine

There are now quite a few Technicians who know the AUM, which is a sweet unit, and most easily uprated to 230 bhp.

On this matter, more power, (so it does nod your head a bit) and in particular, I do agree with Ivor having done a little work this week-end with a very skilled technician.  But If you want,  and need total peace of mind,  pop in to an Audi / BM specialist workshop; It doesn't have to be main Dealer, pay 1/2 an hour's labour. Get an observation report on the sound of those extra 4 valves. Talk to the workshop foreman, not some Kid on reception. 

Pulling Well is a good sign.

[ub7rm]

Thanks for that New Duncan,

72k miles, 5 door.  As far as I can see the engine guard is in the proper position. What I'm not at all sure about is the noise under heavy acceleration.  Under (semi) gentle acceleration the turbo noise (a whistley hiss?) increases smoothly and steadily in line with the revs, under heavy acceleration the noise still increases with revs but then becomes a fluctuating noise.... whisooooo-whisoooo-whisoooo kind of noise instead of a whisssssssss.  Cant believe I just typed that but its the best way of describing it!!

As I say pulls seadily but then you get could get a 1.8 20v GTi non turbo which I would imagine would pull strongly too, so aint sure if I'm loosing horses from some turbo fault thats been there since I bought the car.

Having the brakes done next week so will prob ask them to give me their opinion.  At least it will give them a legitimate excuse to thrash my poor baby (cos you know they do anyway!)