Logically speaking, the car running worse has nothing to do with the fitment of a atmospheric-style BOV... as other's have stated, it's your tuning!

I believe that BOV are a good safety precaution (turbo cavitation protection). It's very difficult to totally prove how they effect outright performance etc, but as long as it works effectively, any brand- even factory will do IMO.

I know there's the age old debate about using or not using one... happens over and over on other forums! The usual argument is:

"I've been running no BOV for years with my TD05 and it's fine"... however, as soon as you point out what can happen to say a VF22 (bent and broken impeller blades etc) the usual reply is"

"yeah, well you'd have to be stupid to run a VF22 without a BOV.. those turbos are a lot weaker!"

Here lies the irony of their statement, they seem to be missing the point... all things being equal, a turbo doesn't just fall apart because it's just simply a 'weaker design', it falls apart because there's some bloody huge backpressures acting on the weaker designed turbo!
By admitting that some turbos cannot be run without a BOV only strengthens the overall argument of indeed using some form of pressure-bypassing device!! /rant off.

I've been using a gfb Stealth FX for a few years now. Great unit because they are designed well (acetyl piston rings etc), can be serviced locally- I get mine done approximately each year, are the largest diameter port in the range, and can run silent or vented to atmosphere. I generally run it closed, only opening for events as I find it gives 'audible feedback' as to where boost is etc at different throttle positions/ different corners etc.

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"...even my Grandma can drive fast in a straight line"