[phuz]

this was just discussed a few days ago...scroll down and read...

a blow off valve will decrease lag on a turbo car that does not previously have one installed, but simply replacing the one you have on the car already won't really help increase performance

 

[phuz]

Re: (needsdecaf)

Quote, originally posted by needsdecaf »

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.

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.