Impreza STI ver.5 BOV Advise


Impreza WRX STI v.5
I bought my STI version 5 from Japan with some modifications:
HKS Fcon V pro Computer, HKS EVC V Boost Controller, APEXI exhaust, HKS intake, NO Airflow meter... and there was no blow off valve

This is a picture of engine, there was no blow off valve, I was confused and decided to install it, but I'm not sure if I made a right decision :embarrest:


When I was taking off foot from accelerator the sound like "trrrrrr" was heard from intake, and the boost was suddenly decreasing to minus -65kPa, so if the back pressure was preventing turbo should I somehow feel it? :embarrest:
I installed blow off valve but I don't feel any difference at all :confused: on low boost I hear the same sound from intake "trrr" :) and on high boost from blow off valve "pss" :bigsmile:. I have seen a lot of subarus, they don'n have such a sound :(

Do I really need Blow Off Valve? :confused:

Please give me some tips, this is my firs car and I'm not experienced with this

Thank you :love:
hey and welcome to the site mate.
you post got stuck oin the mod queue because it contained a pic - you need 10 posts before you can put up links pics.

1st off yes you do need a BOV of some sort to get rid ofthe pressurised air when the throttle is closed otherwise the pressurised are will try to get back out through the turbo itself causing turbo stall. there should have been one as standard.
cant say what the trrrr sound would be
Thank you

The "trrr" sound comes from air filter when the throttle is closed, so this means that the air instead of going out by bov the pressure goes through intake and air filter and causes this sound. where this pressure goes by default? When I got this car bov was disabled, or may be is there any way to let this pressure go somewhere else instead of bov?

For example the stock car has bov just closed, no air goes through. and then I boost up to 1.3 bar, what happens? This is really high pressure and should prevent turbo right? as you sad turbo stall. Should I feel something? I had 1.3 bar but car was going well... I feel no deference. and now after bov was installed the pressure goes also through intake and causes this trr sound :|

This is link of engine picture

Thanks for your reply :)
sorry not clued up on subs.
the BOV should open, due to the pressure, when the throttle is closed. really no air should be going back through the turbo as this will stall it.

why was the BOV taken off in the 1st place?
I don't know, I want to understand why previews owner took off bov, I don't think he made it just like that, because the car has lots of expensive modifications...

I'm guessing you are not in touch with the owner anymore. I can't think why you would remove a BOV there must be some other failsafe in there somewhere.
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