[Needsdecaf]

Re: (JonnyEnglish)

Quote, originally posted by JonnyEnglish »

The need for a BOV or simular device is to release all pressure in the charge pipe when the throttle is closed ie gear changes to stop the trapped compressed air in the charge pipe from stalling the turbine. Thus allowing the turbine to keep (free) spinning until boost is required again ie throttle is depressed.

Correct me if I'm wrong, but I thought it was more to prevent unusually high intake manifold from blowing it up (or more correctly, blowing out a seal or something like that) when the throttle is slammed closed, not to keep the turbo spinning.

 

[Needsdecaf]

Re: (JonnyEnglish)

Quote, originally posted by JonnyEnglish »

Sounds reasonable but it really is to prevent stalling the turbine and I guess a by product it would alleviate excess pressure as you explained. Having said that though the engine and all associated accessories would have been tested and checked for those pressures.

According to Wikipedia, we're both right

This excess pressure could potentially cause damage to the turbocharger's impeller and may also slow or even stop it, thus causing turbo lag when the throttle is pressed again.

 

[Needsdecaf]

Re: (phuz)

Quote, originally posted by phuz »

A BOV or BYpass valve does NOTHING to prevent excess boost. Its ONLY purpose is to release the trapped air when the throttle plate(s) is closed to prevent a stall of the compressor wheel, as per johnnyenglish's explanation.

Where did I say that it prevented excess boost?

You are basically saying what I was trying to put into words.