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Compressor surge problem

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Louis Gibson

Probationary Member
27
0
Jun 23, 2019
Tillamook, Oregon
Have a Greddy type-s BOV (came with the car) and I’m trying to get it adjusted to where I don’t have compressor surge, otherwise known as the “STUTUTU” sound when you let off boost (I’m sure you all know this). The BOV seems to do its job when I’m hitting max boost (meaning it’s just one solid chirp and that’s it). However, if I hit anything lower than max boost, like when I’m shifting through gears a little quick, I can hear the surge not only come from the BOV when I hit about 6-10 psi, but also from the turbo through the cold air intake. They sound a bit different but nevertheless, the same problem. My fear is this is going to ruin the little stock t-25 turbo, being I just had to replace it due to the seals failing.

All help is appreciated!
 
I doubt that your T-25 is getting compressor surge, its more likely the blow off valve bouncing open and closed.

Okay thank you for the insight. I really just don’t have enough knowledge to know the difference LOL..

It definitely sounds like the BOV, cause it has that chirpy tone, however if I let off throttle at like 2-4 psi, there’s a definite surge sound that doesn’t sound like the BOV. But even if it was the compressor surging, would that even be dangerous for the turbo at such a low psi? ‍♂️
 
Compressor surge is bad period, there is no safe level of surge, when it happens the turbine shaft is stalling and in severe cases reversing direction rapidly, this causes broken turbine shafts, loosened compressor nuts, damaged turbine shaft bearings, etc.
 
Compressor surge is bad period, there is no safe level of surge, when it happens the turbine shaft is stalling and in severe cases reversing direction rapidly, this causes broken turbine shafts, loosened compressor nuts, damaged turbine shaft bearings, etc.
So should my BOV be kicking in at lower psi? I’m not sure why the compressor surge is happening then at the low psi range. :/
 
Yes, your bov should be able to open anytime that there is positive pressure at the turbo outlet/intercooler piping and vacuum in your intake.
 
I would agree the sound you're hearing is prob the bov opening and closing rapidly. Do you have the bov on it's own vacuum/boost source? It should have it's own dedicated line, not tee'd into something else.
Surge is bad, but the sound is the compressor chopping up the air as it's being pushed back through (think blowing into a fan). It's not from reversing rotation. Surge on throttle closing is not as much a concern as WOT surge, there were no BOV's in the earlier days of turbo cars. With no bov you got surge every time the throttle shut.
 
If the blow off valve isn't opening when the throttle plate is closed, you will get compressor surge...however it's tough to determine if the noise you're hearing is coming from the turbo itself or the valve. Test the valve first to make sure the diaphragm isn't torn, then consider disconnecting the recirc tube from the intake (cap the hole on the intake) and see if you can hear the noise isolated through the recirc tube and not the air filter. If you can, the valve is adjusted too tight or has too much spring tension and you should consider removing the small spring.

Remember, the spring tension on the valve only controls how quickly the valve opens and how long it stays open under vacuum...it has nothing to do with the amount of boost the valve itself should hold as a properly-designed valve will seal no matter what boost level you're running. If you continue to run a valve that is not opening properly, you may as well not even have a valve installed as the impact on the turbo when the throttle plate closes will be the same no matter how cool it sounds. Eventually it will cause a turbo failure.

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So should my BOV be kicking in at lower psi? I’m not sure why the compressor surge is happening then at the low psi range. :/
There's probably not enough pressure in the piping to even try to open the valve.
 
Sure is nice to have the Turbo Guru back! Glad to see you Justin! :)
 
If the blow off valve isn't opening when the throttle plate is closed, you will get compressor surge...however it's tough to determine if the noise you're hearing is coming from the turbo itself or the valve. Test the valve first to make sure the diaphragm isn't torn, then consider disconnecting the recirc tube from the intake (cap the hole on the intake) and see if you can hear the noise isolated through the recirc tube and not the air filter. If you can, the valve is adjusted too tight or has too much spring tension and you should consider removing the small spring.

Remember, the spring tension on the valve only controls how quickly the valve opens and how long it stays open under vacuum...it has nothing to do with the amount of boost the valve itself should hold as a properly-designed valve will seal no matter what boost level you're running. If you continue to run a valve that is not opening properly, you may as well not even have a valve installed as the impact on the turbo when the throttle plate closes will be the same no matter how cool it sounds. Eventually it will cause a turbo failure.

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There's probably not enough pressure in the piping to even try to open the valve.
Thank you for the response and the insight on this issue. I really appreciate it!

few questions: in the picture, what would be considered “contact” for the screw on the BOV? Just want to make sure I do this right LOL

and second, I tried teeing a boost source into the BOV from where the boost guage gets its boost source from (off the intake manifold). Was this a mistake? I ended up losing vacuum and the BOV fluttered like a Toyota Supra no matter the setting LOL
 
and second, I tried teeing a boost source into the BOV from where the boost guage gets its boost source from (off the intake manifold). Was this a mistake? I ended up losing vacuum and the BOV fluttered like a Toyota Supra no matter the setting LOL

BOV Should always have an independent source of vacuum with nothing Teed into it.. Typically a good source of vacuum for your Aftermarket Boost gauge is going to be off the vacuum line for the Fuel Pressure Regulator. Remember to never trust the factory boost gauge its not an accurate reading!
 
And REALLY....you shouldn't tee into the vacuum line to the fuel pressure regulator because if you spring a leak in the line then your tune goes LEAN under boost since it won't rise 1:1
Just sayin. Yes a lot do tee off of it but if you can find a TB source for boost, use it for the boost gauge. Leave the FPR line dedicated too, if possible. I run my car hard, if it didn't raise the fuel pressure, my car wouldn't be happy and I hope I would be watching my AFR gauge and let out of it.
 
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