Z4 35is turbo whine at low rpm, nedd help!


Oct 29, 2023
hi guys

My name is vincent and i live in france.
I owned a z4 35IS for 2 years and I have some whine problem with my OEM turbos.

Z4 35is WAGNER EVO1 intercooler, NGK one step colder spark plugs and NGK coils (only 10000kms on them), RB PCV valve since one month.
MHD stage 1/1+ or 2 depends on my desire.

Bought it in june 2020 with 40000kms on odometer
Ran it up to september 2020 full stock without any problems
Installed FMIC/coils and sparksplugs and then pit MHD V9 stage 1+ E50 without issues.
Few days later, I Tried V10 1+ E50 and immediately noticed a whine at low rpm after my first MHD log....

here is a record of the whine on my forst turbo oem set:

Then I tried to understand why during one years, read lot of thread on E90 forum, cheked everything (rear inlet correctly set on turbo, no radial or axial shaftplay, logs etc...) and nothing was wrong

I succeed to delete whine by installed VRSF downpipe and set rattle fix parameter in MHD @10% and whine disappeared but it came back as soon as I put back my oem DP (because I discover that I have 1M DP because my car is a z4 35IS)

As this noise made me crazy I decided to change my turbo set (after 10000kms on it with the whine) by another OEM ones (My goal is only modest tune stage 1 or 2 V10 is ok for me i like the naturally aspired boost curve more than 2+ one.) That was at the beginning on september 2023.
Ran the car for 200kms on V7 stage 1+ 93 octane and no whine. I was so happy!
Then I put V10 stage 2 targeting 14,5psi and whine came back, very faint but it was here.

Now I downgrade to stage 1 V10 E50 targeting only 13 psi and whine continue to increase....
I have the impression that whine become louder each time I run my car above 6000rpm but maybe it's in my head...

Recently I asked to a specialiste near paris to bench my old set and result was that both turbo were unbalanced with "orange peeel" efefct on the compressor blade, more on rear turbo. Here is a video I posted on E90forum to explain the results:

For my turbo specialist, "orange peel" effect could explain the whine and it's du to a compressor wheel overspeed.
We can see it on this picture of my rear compressor wheel:

He said to me that oem compressor wheel is made with aluminium and is not strong. He adviced me to change compressor wheel for a forged billet one.
Before to do that I have to understand why my turbos failed when lot of you guys run more demanding tune without any problem.
I'm not the only one concerned by this whine, some people report that problem and some of them already tred to change there turbo set and problem came back as soon as they tune their car....(I'm in talk with Studio54 for example wich has exactly the same problem than me)
My logs are ok, WGDC seems to be good so no leak, I just have bad postshift timing correction on V10, far less on V7 (maybe because there is no throttle closure on shift on V7 compare to V10 or V9)

Here is my last log on V10 stage 1:


Sorry for this big first post but I saw any post on this forum talking about my problem.
Thanks to you to help me if you can.


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