[AdventureNoodle]

Hey all, my custom tune makes this sound when I let off. Sounds like an old JDM flutter. How bad is this and should I tune it out? Thanks!

https://youtube.com/shorts/lI4OYD7VPlA?feature=share

[M2 Ziggy]

Sounds amazing like a late 90s wrc car but it puts extra load on bearings so probably not good in long term

[///393]

Sounds like compressor surge, which wasn’t good in the 90s either so I can’t imagine this is a good thing. Likely adding wear on the turbo

Does sound sick though.

[AdventureNoodle]

Originally Posted by M2 Ziggy

Sounds amazing like a late 90s wrc car but it puts extra load on bearings so probably not good in long term

I know right lol. Probably gonna tune it out

[AdventureNoodle]

Originally Posted by wilson kop

Sounds like compressor surge, which wasn’t good in the 90s either so I can’t imagine this is a good thing. Likely adding wear on the turbo

Does sound sick though.

Wouldn’t compressor surge be under throttle? Since this is off throttle isn’t it a lot more benign? It’s a Pure Stage 2 so it’s a POS anyways lmao

[M2 Ziggy]

I thought it’s caused when you lift off the throttle the exhaust gas stops spinning turbine side and the air in compressor side suddenly has nowhere to go against the closed throttle body so spins rapidly as there’s less gas flow on turbine side

[F87source]

Originally Posted by AdventureNoodle

Hey all, my custom tune makes this sound when I let off. Sounds like an old JDM flutter. How bad is this and should I tune it out? Thanks!

https://youtube.com/shorts/lI4OYD7VPlA?feature=share

It is not good for the turbo, but largely depends on load and rpm. High load high rpm high boost surge is very very bad, low rpm low load low boost surge is "tolerable" for longer but not really ideal.


It could also be your diverter valve preventing the boost from dumping properly. Some overly spring diverter valve upgrades do cause this issue.

Originally Posted by M2 Ziggy

I thought it’s caused when you lift off the throttle the exhaust gas stops spinning turbine side and the air in compressor side suddenly has nowhere to go against the closed throttle body so spins rapidly as there’s less gas flow on turbine side

Yes your decription is pretty much spot on except for the last part.

So what happens is when you let off, the throttle body closes and the waste gate opens so the exhaust side has alot less pressure driving the turbine. But the large build up in pressure in the charge air duct resists the flow of the compressor wheel so it actually doesn't spin rapidly. What actually happens is the compressor blades stalls - aka the blades no longer can "grip the air" and push it, because there is no where for the air to go. So the air flow "falls off" the compressor wheel and this causes the fluttering sound. It is actually horrible for the turbo because it puts a lot of strain on the bearings and the compressor wheel and blades.

[EvanP246]

This has been argued to death on many forums over many platforms. The long and short of it is that on throttle surge is bad and off throttle surge is fine.

I have not run a blow off valve on several of my cars (Evo 8 & 9, MR2, 500 hp Celica GT Four) for years and many miles of hard abuse at high boost with no detrimental affects on the turbocharger.
I would note that these were MHI or Garrett turbos and they are known for their robustness, not all turbos are created equal.

Pic of the GT Four:

[M2lci_]

After I installed an open filter intake I noticed my turbo makes the same flutter although not quite as loud as your Pure stage 2 becuase I'm fully stock. Only happens in comfort and Traction mode, with sport and sport+ producing the typical OG 'brap' let-off sound. Personally I love the flutter, but will this potentially lead to issues down the line despite being how the car sounds from factory? I assume it made this sound the whole time but the factory intake muffles the sound enough to make it inaudible.

[F87source]

Originally Posted by M2lci_

After I installed an open filter intake I noticed my turbo makes the same flutter although not quite as loud as your Pure stage 2 becuase I'm fully stock. Only happens in comfort and Traction mode, with sport and sport+ producing the typical OG 'brap' let-off sound. Personally I love the flutter, but will this potentially lead to issues down the line despite being how the car sounds from factory? I assume it made this sound the whole time but the factory intake muffles the sound enough to make it inaudible.

The factory sounds really isn't flutter, it's more a whoosh from the diverter valve recirculating air back to the intake tract. It's more audible with an intake because it removes the factory silencer.

[M2lci_]

So just to clarify, this sound is the diverter valve and not compressor surge?

https://m.youtube.com/watch?v=0dq5Z455CaY

[F87source]

Originally Posted by M2lci_

So just to clarify, this sound is the diverter valve and not compressor surge?

https://m.youtube.com/watch?v=0dq5Z455CaY

No that's compressor surge.

The diverter valve relieve pressure just makes a whoosh. Sometimes an agressive diverter valve upgrade (one that keeps the valve shut as long as possible in effort to reduce turbo lag) will induce a slight bit of surge, but nothing that agressive.

[M2lci_]

Originally Posted by F87source

No that's compressor surge.

The diverter valve relieve pressure just makes a whoosh. Sometimes an agressive diverter valve upgrade (one that keeps the valve shut as long as possible in effort to reduce turbo lag) will induce a slight bit of surge, but nothing that agressive.

So my car, and other OGs I've heard all make this exact noise. Assuming this is just the way the car comes from factory would installing an upgraded DV be worth it, especially because I want to tune the car later this year, or since this sound only occurs in 2 driving modes it isn't worth it?

[VicF87OG]

My OG m2 sounds the same after only installing the CTS intake and no tune.
My next steps are GFB+ , 200 cell sport car
and all the usual bolt ones so that I could
Tune to MHD stage 2 safely .

[F87source]

Originally Posted by M2lci_

So my car, and other OGs I've heard all make this exact noise. Assuming this is just the way the car comes from factory would installing an upgraded DV be worth it, especially because I want to tune the car later this year, or since this sound only occurs in 2 driving modes it isn't worth it?

Are you sure it sounds exactly like that video? Because that was a really distinct and intense fluttering.

Because this is what intakes on the n55 engine is supposed to sound like, and I've never heard really bad compressor surge occur stock or with just an intake.

https://youtube.com/shorts/mPI7-_fABTk?feature=share

335i:

There's a tiny bit of flutter on this one: https://youtube.com/shorts/R2mKda81Rs4?feature=share

But nothing to the same intensity as that video you shared, which imo is past the point of being safe. That's going to cause some real wear and tear on the turbo's bearings.




The only time I have ever heard compressor surge occur badly was when there was an upgraded diverter valve as well. And this was with early generation dv+ valves with the piston spring being too stiff. This has changed and gfb has decreased the spring stiffness to stop the compressor surge from occuring. In regards to the turbo smart I'm not sure what they've done. But to answer your particular question if it's occuring stock and you don't have any codes from the diverter valve being stuck or failing, then it should be ok. I'd probably remove the diverter valve to ensure blow by isn't gunking it up. But you should be ok to mod. A diverter valve is a pretty good mod regardless because it really does enhance the throttle response. Also the tune shouldn't be causing this surge.







Here's a video explaining compressor surge from Kyle engineers (a PhD aerodynamicists who worked for Mercedes F1, so he's legit) :

[F87source]

This is generally what happens when your diverter valve fails:

https://youtube.com/shorts/3NazaWl4eTU?feature=share





I'm willing to say in all those videos where you hear the extremely agressive compressor surge there was an aftermarket diverter valve as well. I've seen this before during my m235i days when gfb dv+ diverter valves were new and the piston springs were too strong, or the plunger springs were too strong and the magnetic solenoid was too weak to retract the plunger as a result of this spring and the result was surging. This has been fixed on the new gfb valves so it should be perfectly fine now.


I've even seen this happen on the turbo smart valves because they're too agressive in trying to retain boost.

[AdventureNoodle]

My surge noise is tune dependent. The sound changes between OTS and Custom tune. It has to do with the throttle plate and how open / closed it is once you come off throttle

[F87source]

Originally Posted by AdventureNoodle

It has to do with the throttle plate and how open / closed it is once you come off throttle

That is true, if your throttle body closes extremely rapidly and the diverter valve cannot vent fast enough you will have some small amounts of surge.


IMO it won't be a hugely bad thing unless it is really really agressive surging.