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Subaru Impreza sti v.5 JDM NO Blow Off Valve?
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Old 05 Dec 2009, 09:49 PM   #1 (permalink)
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Subaru Impreza sti v.5 JDM NO Blow Off Valve?

Hello
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, adapter pipe blanked off.

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 the right decision



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

Do I really need Blow Off Valve? Is any scenario when the engine is remade like this, (adapter pipe blanked off).

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

Thank you
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Old 05 Dec 2009, 10:08 PM   #2 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

Hi mate


WRX BOV Blow Off Valve

There are three types of blow off valve systems you can choose for your impreza.

1. 100% Atmospheric Blow Off Valve

2. Adjustable Recirculatory-Atmospheric Blow Off Valve (Atmostpheric & Return)

3. Recirculatory Blow Off Valve (OEM)

100% Atmospheric Blow Off Valve

The 100% atmospheric blow off valve is safe to use if you have TBE, intake, and no cats. You might also want to consider purchasing a wideband air-fuel ratio gauge like AEM UEGO or LC-1 and have it installed into your exhaust (length from turbo according to directions of wideband, aem uego wants at least 36" to prevent burning of sensor)

The atmostpheric blow off valve can do damage to your car if you aren't properly modified for it. They are bad for stock cars because the lack of air entering the intake tract is less than expected, so the car runs rich in between gears and can cause afterfire. Afterfire is when unburnt fuel in the exhaust system is exploded post-turbo due to heat generated from the turbo. Afterfire flames can shoot out from your exhaust as far as three feet with only a BOV, TBE, intake, and no cats. This rich condition that causes flames also helps keep your spool, due to extra gases in the exhaust tract creating pressure on the blades during the rich period.

Atmospheric blow off valves also help reduce turbo lag and spool time. There is no air being "forced" into the natural flow of your intake, which slows down the turbo spool. The incomming air from the recirculatory blow off valve acts like an air brake on the fins of the turbo intake. By removing this air, and creating the rich condition between shifts, this removes restriction of the intake and increases the force pushing the exhaust part of the turbo which in theory keeps the spool spinning. The spool time is actually noticeable if you have installed a turbo inlet, maf hose, tbe, up-pipe, and removed cats. Up-pipe is optional, but is usually included when you remove all the cats. (Cat in the up pipe)

Adjustable Recirculatory-Atmospheric Blow Off Valve

The adjustable recirculatory-atmostpheric blow off valve is a great choice if your car is stock because it allows an adjustable amount of air to enter the turbo inlet. This prevents the car from running at such extreme rich conditions as some vehicles will experience when using the 100% atmospheric blow off valve. If the 100% atmospheric BOV is causing your car to stall, or making it shoot too much fire, you might want to consider the adjustable recirculatory-atmospheric blow off valve.

The adjustable factor of this part allows you to tune the bov air amounts you want. You basically have to choices, LOUD, or quiet. Loud being vented to atmosphere, and quiet vented back into the turbo inlet. If you want to decresase spool time, and not have the annoying woosh of atmospheric blow off valves, you should consider the adjsutable recirculatory-atmospheric blow off valves.

Recirculatory Blow Off Valve (OEM)

The recirculatory blow off valve is not only bad for your car, but it reduces fuel economy and places additonal stress on your turbo system that is not needed. Under extreme conditions and use, it can freeze and create enough back pressure to blow the intake manifold clean off the block. If your blow off valve fails and you notice your boost not going away, turn off the vehicle asap. This will let the boost vent naturally out through the intake rather than forcing it out in form of explosion.

There are recirculatory blow off valves that are aftermarket, but I personally don't see any use for these at all. You need to get rid of the 100% recirculatory blow off valve and at minimum buy . hth
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Old 05 Dec 2009, 10:23 PM   #3 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

I didnt write that, it was in a book ive got. It quite good though
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Old 05 Dec 2009, 10:33 PM   #4 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

lol Ian v good read
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Old 06 Dec 2009, 09:40 AM   #5 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

Dont have a "blow off" valve on mine.
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Old 06 Dec 2009, 05:32 PM   #6 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

RAianM
Interesting

thanks
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Old 16 Feb 2010, 02:27 AM   #7 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

Bumpin an old thread.. so is no BOV a BAD thing if you are running Stock boost, with Intake and exhuast mods?
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Old 16 Feb 2010, 08:08 AM   #8 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

Most people around here dont have them. Not good for our cars. Been told that i should defo not have 1 on my Ra
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Old 16 Feb 2010, 08:37 AM   #9 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

Damn good read, thanks for sharing
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Old 19 Feb 2010, 01:18 PM   #10 (permalink)
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Re: Subaru Impreza sti v.5 JDM NO Blow Off Valve?

Most of the turbos cannot take the back pressure and can damage the bearings.
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