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thoughts on turbo flutter?

15K views 46 replies 15 participants last post by  slindborg 
#1 ·
i have watched a lot of videos on youtube about turbo flutter. some say that it is harmful to the turbo some say it doesnt have a affect as the turbo is made to withstand the pressure. i want to make my bmw 120d m47 163bhp flutter but not sure if it will damage my turbo
 
#4 ·
#6 ·
Our modern diesels at work have a butterfly throttle but its in the intake (IAT intake air throttle)
 
#8 ·
B NEGATIVE said:
Turbo flutter is normal,it wont damage anything,if it bothers you then fit a wastegate. I think you are confusing wastegate flutter with turbo flutter,they are different things.
All turbos have a wastegate already (barring some Porsches etc) Do you mean diverter valve or blow off valve, sometimes called a dump valve, though dumping to atmosphere should be left to 90s Jap/ford cars.
 
#13 ·
Trying to make a boggo 4 pot diesel sound decent is a waste of time IMO. I've nothing against BOV's, had a nice one of my old Focus ST, but don't see the point with a diesel.
 
#15 ·
OneTwenty said:
Trying to make a boggo 4 pot diesel sound decent is a waste of time IMO. I've nothing against BOV's, had a nice one of my old Focus ST, but don't see the point with a diesel.
It sounds like a BOV was suggested as a solution to something that the op wasn't asking for.

As I said above and the owner confirmed, he wants the lift-off "coooo" sound which is a result of the veins of the turbo being held open after giving it full power then taking your foot off the accelerator quickly (usually at about 2.5krpm).

This sound can be heard once the backbox is removed or with a straight through exhaust and is in no way related to a wastegate (which a diesel doesn't have) or a blow-off or recirculating valve (which a diesel doesn't have/need)

Edit: also a diesel with a straight through has quite a nice rasp on full-throttle! It's all personal preference though and agreed you'll never make it sound like a 5-pot petrol like in the ST
 
#16 ·
DGJ123d said:
OneTwenty said:
Trying to make a boggo 4 pot diesel sound decent is a waste of time IMO. I've nothing against BOV's, had a nice one of my old Focus ST, but don't see the point with a diesel.
It sounds like a BOV was suggested as a solution to something that the op wasn't asking for.

As I said above and the owner confirmed, he wants the lift-off "coooo" sound which is a result of the veins of the turbo being held open after giving it full power then taking your foot off the accelerator quickly (usually at about 2.5krpm).

This sound can be heard once the backbox is removed or with a straight through exhaust and is in no way related to a wastegate (which a diesel doesn't have) or a blow-off or recirculating valve (which a diesel doesn't have/need)

Edit: also a diesel with a straight through has quite a nice rasp on full-throttle! It's all personal preference though and agreed you'll never make it sound like a 5-pot petrol like in the ST
It wasn't that great on the ST though either tbh, sounded like a hamster sneezing although with the other mods it all added up to sounding half decent!! :D The only decent BOV and chatter/turbo stall sounds come from the big engined Jap motors IMO, 2JZ Supra, GTR etc.
 
#17 ·
This is one hell of a confusing thread :lol2:
Removing a back box has nothing to do with turbo flutter..
This is turbo flutter, is that what you are after? (Video below).
If so then it's heard through the intake.
When I installed my bov it was a bit tight, the n54 has a pretty decent sounding turbo flutter (on my car anyway) :D but as much as I wanted to keep it that way it's no great for the turbo as it's basically air going back against the compressor wheel.

 
#18 ·
drifterr said:
This is one hell of a confusing thread [emoji38]
Removing a back box has nothing to do with turbo flutter...
You're right, it has nothing to do with turbo flutter. However the op drives a diesel which doesn't have a blow off valve and wouldn't make a turbo flutter noise in any case. I think wires have been crossed by people mentioning BOVs in a diesel thread [emoji41]

He wants the closing veins sound like you can hear on this one from about 10 seconds in...



This is achieved by removing the backbox or going straight through.
 
#20 ·
Are there only like 2 people who have owned a turbo car before here? :lol2:

I assume we are all talking about this noise:



A Dump valve is nothing to do with turbo "flutter"/"chatter"/compressor surge/owl noises which I will refer to as the pigeon noise from now on, it actually reduces the noise as air is venting elsewhere in the system. That said, some BOV's replicate the pigeon noise, this is usually your best route on a diesel (see below)
The noise comes from the pressurised air that has travelled through the turbo but has nowhere to go when the throttle plate is closed, so it comes back out the front of the turbo, through the blades which makes the noise.
All turbo cars with a throttle plate make the noise, but most cars have a suppressor fitted somewhere near the air filter so you dont hear the noise, in the case of the N54 the closed inlets do the job pretty well too. As someone else has said, a turbo without a wastegate will just keep producing boost until it blows up so unsurprisingly it doesnt happen.
Diesel cars often dont have throttle plates to close the system so its a lot more difficult to get the noise, I believe very high boost can do it though.

Size of engine is irrelevant, level of boost, hard intake pipes and type of air filter make a lot more difference.
It used to be said that it damages a turbo but Ive never seen hard evidence of this, as it happens the other route to the noise through atmospheric BOV's is worse as they can cause fuelling issues.
 
#21 ·
docwra said:
Are there only like 2 people who have owned a turbo car before here? :lol2:

I assume we are all talking about this noise:



A Dump valve is nothing to do with turbo "flutter"/"chatter"/compressor surge/owl noises which I will refer to as the pigeon noise from now on, it actually reduces the noise as air is venting elsewhere in the system. That said, some BOV's replicate the pigeon noise, this is usually your best route on a diesel (see below)
The noise comes from the pressurised air that has travelled through the turbo but has nowhere to go when the throttle plate is closed, so it comes back out the front of the turbo, through the blades which makes the noise.
All turbo cars with a throttle plate make the noise, but most cars have a suppressor fitted somewhere near the air filter so you dont hear the noise, in the case of the N54 the closed inlets do the job pretty well too. As someone else has said, a turbo without a wastegate will just keep producing boost until it blows up so unsurprisingly it doesnt happen.
Diesel cars often dont have throttle plates to close the system so its a lot more difficult to get the noise, I believe very high boost can do it though.

Size of engine is irrelevant, level of boost, hard intake pipes and type of air filter make a lot more difference.
It used to be said that it damages a turbo but Ive never seen hard evidence of this, as it happens the other route to the noise through atmospheric BOV's is worse as they can cause fuelling issues.
I never meant a bov is required for turbo flutter, was just stating that my bov setting was to tight causing the flutter.
When it did flutter the sound clearly came from the rear inlet pipe and not from my bov!
 
#23 ·
docwra said:
Diesel cars often dont have throttle plates to close the system so its a lot more difficult to get the noise, I believe very high boost can do it though.
I got the noise on my old Leon Cupra TDI when I had a Milltek straight through fitted, and also in my last car which was a Renault Laguna that I took the backbox off when one of the exhaust mounts was loose. Both only 150bhp and around 20psi of boost which is pretty normal in a diesel. As you said there's suppressors in the intake (the air filter itself being one) so to get the noise out on a diesel requires an unsupressed exhaust instead.

I think you explained it far more technically than I could though [emoji4]
 
#24 ·
I mentioned the BOV, but not for a diesel. Someone mentioned wastegate flutter which would just mean it's broken or not working. Wastegates are controlled by an actuator on the hot side of the turbo and only open to bypass exhaust gas away from the turbo to reduce boost pressure.

As someone said, no butterfly valve so no BoV is required on a diesel. Nor will you get compressor surge, or chatter as per the videos, because it needs the butterfly valve (throttle plate) to pressurise the inlet pipe.

On a petrol car, a tight BoV will cause compressor surge. It's just the compressed air having no where to go when the throttle plate closes, so it goes back through the turbo and stalls it.

You can fit a BoV to a diesel car, but you have to add a plate to close and divert the air to atmosphere through the BoV, making the chirp. These can be added solely for that purpose, but there is no performance gain and it's a bit, well, silly really.
 
#25 ·
We all know the differences, but the discussion moved from flutter/compressor stall to BOVs, which I agree is a slight tangent but that's just the way it went. :D

Either way, it's still a bit pointless imo making a diesel sound good.
 
#26 ·
This thread is funny.

That diesel vid above, that's just the sound of a turbo spooling down.... You're never going to get flutter from a diesel because no throttle plate.

There's a guy in my local town who's fitted a BOV and big exhaust to his TDI Golf, makes me **** myself laughing when this half hearted ptshhh goes off as he drives by, not to mention the god awful noise from the drainpipe exhaust. :lol2:
 
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