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I was running a Cobb OTS tune while waiting for my custome tune date while running a catless DP and was having overboosting problems for obvious reasons, but after a while I started noticing a high pitched repetitive chirping noise mid pull/ at high boost pressure usually in 3rd or 4th and sometimes 2nd, not like one chirp but more like 10 in the matter of a couple seconds. I assumed it was some sort of boost leak as I noticed a very slight decrease in power when that noise occurred and decided to take it in to get it looked at the day it was getting tuned. The shop said there was no boost leak and tuned it and my overboosting problems went away, but driving home I notice the same sound and slight power loss. At lower rpm shifting I also notice a bov flutter so I’m assuming something is up with the BOV. I haven’t seen anyone else with this sound so if you have any ideas lmk and apologies if this is a stupid easy fix or common problem.
 

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I bought the car with an aftermarket BOV installed and I will check today to see which one but looking through the wheel well it looks like the mountune one.
 

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Sounds like the BOV is venting a bit of pressure to keep boost levels capped.
 

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Incorrect, that job is given to the wastegate. Unless maybe you’re ecu is trying to run less than wastegate spring pressure, it may do that but I don’t think our system is even smart enough for that
 

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Incorrect, that job is given to the wastegate. Unless maybe you’re ecu is trying to run less than wastegate spring pressure, it may do that but I don’t think our system is even smart enough for that
Sounds like the BOV is venting a bit of pressure to keep boost levels capped.
I took it back into the shop today and the tuner told me that he thinks that sound is controlling the boost levels so I guess you would be correct. I’m looking into a gfb blow off valve anyways so if there is a problem with the bov then this should solve that. It’s just weird because I haven’t heard anyone else’s sound like this but it feels good so I’ll just go with it.
 

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Incorrect, that job is given to the wastegate. Unless maybe you’re ecu is trying to run less than wastegate spring pressure, it may do that but I don’t think our system is even smart enough for that
Then why do people install the BRA with a BOV?.... Our cars have some fancy electronics/tuning and don't operate the same as old turbo cars.
 

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Just adding a bit of info for you guys to think on.

While running aux fuel, and an aftermarket BOV with a BRA, the car would see-saw on part throttle. After going back to the OEM BOV, the issue persisted. After routing the vacuum hose back to the stock sensor, therefore back to the stock BOV and electronically controlled BOV actuation, the car was no longer see-sawing, and was driving smoothly. The difference is that I could hear the BOV constantly venting into the intake in a see-saw pattern to keep the car smoothly revving. I'm not an expert but it feels like the ECU will control both the BOV and wastegate to maintain pressure, and AFRs, instead of relying on only the wastegate.

I've seen this same behavior with an ST and an aftermarket BOV with a boost reference, and it doesn't happen without AUX fuel.
 

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Then why do people install the BRA with a BOV?.... Our cars have some fancy electronics/tuning and don't operate the same as old turbo cars.
the reason we install the BRA is because the factory system has a cool, but annoying, way of keeping turbine speeds up while off-throttle. A system you’d never notice since from factory out cars are a closed recirculated system, not a vent to atmosphere like aftermarket bov.

the wastegate is what controls the amount of ‘boost’ you can run through your turbocharger, by opening and letting exhaust gassed bypass the turbine. The lowest psi our cars can run (I think) is 14psi, or whatever our factory wastegate spring is. If for some reason the car wanted to run zero boost, it could just open the BOV but I don’t see any reason it would want to do that.

what you are referencing is the noise that the BRA gets rid of. In simple terms, when we are off throttle, or very light throttle applications, the ECU keeps the BOV open. It does not create any boost, but that also means that there is little to no load against the compressor wheel, letting it spin at a high rpm with little resistance. So when we go back on throttle the response is quick. When you have a BOV that vents to atmosphere that noise is annoying as all hell.

I’m well aware of how our cars don’t operate like old turbo cars.
 

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the reason we install the BRA is because the factory system has a cool, but annoying, way of keeping turbine speeds up while off-throttle. A system you’d never notice since from factory out cars are a closed recirculated system, not a vent to atmosphere like aftermarket bov.

the wastegate is what controls the amount of ‘boost’ you can run through your turbocharger, by opening and letting exhaust gassed bypass the turbine. The lowest psi our cars can run (I think) is 14psi, or whatever our factory wastegate spring is. If for some reason the car wanted to run zero boost, it could just open the BOV but I don’t see any reason it would want to do that.

what you are referencing is the noise that the BRA gets rid of. In simple terms, when we are off throttle, or very light throttle applications, the ECU keeps the BOV open. It does not create any boost, but that also means that there is little to no load against the compressor wheel, letting it spin at a high rpm with little resistance. So when we go back on throttle the response is quick. When you have a BOV that vents to atmosphere that noise is annoying as all hell.

I’m well aware of how our cars don’t operate like old turbo cars.
Yes I'm aware of this, and that's what I was alluding to with my comment. The OP already mentioned that the tuner confirmed my theory, so it appears it does it during full boost as well. Could be something specific to the tune, but either way it sounds like the case is solved and it's the BOV venting. This is why I just went with an upgraded BPV. Still get enough sound, but without hearing the venting during regular driving.
 

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Yes I'm aware of this, and that's what I was alluding to with my comment. The OP already mentioned that the tuner confirmed my theory, so it appears it does it during full boost as well. Could be something specific to the tune, but either way it sounds like the case is solved and it's the BOV venting. This is why I just went with an upgraded BPV. Still get enough sound, but without hearing the venting during regular driving.
Yea, I was still having overboost issues in higher gears getting around 27/28 psi according to the AP. I took it in again a number of times after overboosting issues allowing my tuner to find that limit. After the last tune I’ve gone pretty hard in 6th getting to ab 110 mph (in Mexico) and no overboosting which also minimized the chirping/squealing noise throughout all gears. I guess it was in need of a tuning adjustment in the end.
 
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