Blow off valve

[Donato]

What is their purpose?

Regards

Donato

[20B_boy]

When u let off the throttle and the butterflys close the pressure thats in the intake system has no hwere to go. Without a BOV fitted, this gets forced back to the turbo. The pressure on the compressor wheel can a) stall the spinning turbo with the effect that you get increased lag when u go back into the throttle and b) in extreme cases the pressure can snap the turbos shaft (the bit that has the turbine and comparessor wheels attached to each end!). Thats my rather week and simplsitic \'understanding\' any way!

THeres a lot of umming and arring as to whether a BOV is really necessary or not or in fact if it really does much at all. There was a big debate on one of the ausrotary threads recently I think. Most said dont bother...

[J4P RX]

Why would people say dont bother with a BOV when it comes with a recirc already?

Its pretty much the same thing, and cant be a bad thing as far as I can see?

[iaint]

This is something that is part of the standard setup on an FD (and I assume all trubo\'d cars) - in the FD it\'s vented internally (into the exhaust) which is why it\'s not loud and leary.  It\'s basically doing the same as what is called the wastegate I think.

Iain

[Donato]

Thanks, just wanted to find out if it was necessary or not, personnaly i don\'t like the sound so won\'t be bothering with one...

[J4P RX]

Originally posted by iaint
This is something that is part of the standard setup on an FD (and I assume all trubo\'d cars) - in the FD it\'s vented internally (into the exhaust) which is why it\'s not loud and leary.  It\'s basically doing the same as what is called the wastegate I think.

Iain

It vents back into the airbox, and its not the same as a wastegate.

Lee

[J4P RX]

Originally posted by Donato
Thanks, just wanted to find out if it was necessary or not, personnaly i don\'t like the sound so won\'t be bothering with one...

You will already have one - its a standard thing.  You have have one that recircs though and not one that vents to atmosphere.  thats where the noise is from.

Lee

[20B_boy]

Originally posted by J4P RX
Why would people say dont bother with a BOV when it comes with a recirc already?

Its pretty much the same thing, and cant be a bad thing as far as I can see?

Yes, I know! And I\'m not saying it is a bad thing. I\'m just saying that lots of people run without them it seems. A few of the aussies were saying how gay the psssht-thing was these days and Rice amongst others replied by saying they were unnecessary - in as elegant a way as Rice seems to say any thing

Iain - as Lee said: yes it is part of the stock FD setup.  No it doesnt vent into the exhaust - it vents back into the intake tract via the air box or induction kit if u have one. If u disconnect the pipe to the aribox on a stock car u get the \'psshtt\'. No its nothing like/to do with the wastegate - the w/gate controls the amount of boost the turbo is allowed to produce by venting excess exhaust gas out your exhaust when target boost is reached.

[iaint]

Ta Rich/Lee!

That makes sense now I think about it as i could hear it when I forgot to pop the airbox back on once!

Iain

[Ricco_04]

No it doesnt vent into the exhaust - it vents back into the intake tract via the air box or induction kit if u have one. If u disconnect the pipe to the aribox on a stock car u get the \'psshtt\'.

Would it do any damage if you did disconnect the pipe to the aribox, and should/can you disconnect it at both ends?

Doing this, apart from the psshtt noise, would it make any other differences - power, fuel consumption etc

(can u guess im not technical :rolleyes:  )

[bobster]

You can disconnect it from the airbox. Make sure you cap the hole where it used to connect.
If you diconnect the other end from the turbo pack you will get the \'pssssssssssss\' noise when the turbo starts spooling. Thats because all of the pressurized air is escaping out the hole.

IMHO
In terms of performance, an atmospheric dump valve is better than the recirc as it vents air that has already been heated by the turbo, away from the induction tract. I don\'t know if the preheated air would make any significant changes ....but every little helps.
I know my car pops and bangs alot less with the atmospheric valve.