LUP15, There are a million posts on BOVs on forums around the world. At least 50% of what is written is tripe. Many people don't understand the purpose of a BOV or how it functions. Look at all the idiots that want to put a BOV on a non-turbo car for example.
Most stock BOVs are 100% bypass, that is, all the air vented upon throttle closure goes back to the turbo inlet. The reason for changing to an after-market one is either: 1 - to get one that holds more boost; 2 - to allows partial or full vent to atmosphere (VTA) and/or 3 - to make a venting noise; 4 - to enable adjustment . Most stock BOVs lack any adjustment.
Changing from a stock BOV will not improve performance per se, all other things being equal. What it can do is solve the problems of a leaky BOV (rare); solve the problem of a BOV that is fine at stock boost but which leaks under boost above stock specs such as when boost control is tweaked up; or as a protective measure intended by the manufacturer against inadvertent boost spikes or deliberate tinkering.
But most importantly, it can enable a BOV to be adjusted. By doing so, the performance benefit that comes is not power, but arises by tweaking the BOV so just enough air is vented to Bypass to keep the turbo from stalling, while the remainder of the air under pressure remains in the plumbing and is thus still under some pressure so that there is less lag to full pressure build-up when you get back on the throttle - hence improved throttle response and apparent "quicker turbo spool up".
This should be YOUR reason to replace your stock BOV if it is not already adjustable, which I assume is the case seeing your handle tells me you have an MPS3. Set it up by screwing it in so you don't get backfires (if VTA or partial VTA), but not so far as to cause compressor stall - you'll feel it when you get there, so back off from that point. Make 1/4 turn changes and drive each time. It can take days. Best to take your time and not try to do it all in a day. I still believe the Turbosmart is the most user friendly around - it is a 3:1 BOV and the base is adjustable to you can get it sitting right to suit your plumbing. It can be fitted to the MPS3 in minutes. Don't drop anything down the intake pipe - block up the exposed flange with clean rag!
But beware of anecdotal tales from folks, who don't know much, about how it "adds heaps of power". If they say this then the odds are that they may not even know how to adjust one. If they get it right first off and report better throttle response and "more power" it is possibly just dumb luck - remembering also that better response often feels like "more power" too.
Cheers
Last edited by Doug_MPS6; 04-08-2010 at 04:24 PM.
CP_e Standback & PNP; CP_e 3" SS Downpipe; Corksport FMIC with Top-mount K&N filter & OEM Ram CAI; Turbosmart BOV; Dashhawk; Prosport Boost Guage; JBR solid shift bushes; DBA 4000 Wiper-Slot front rotors; Hawk Ferro-Carbon HPS Street front brake pads (@ 69,000km); Sumitomo HTRZIII's in 225/45 x 18