Does a BOV add any horse power? and what's the difference between stock and aftermarket?

 

no. THey prevent the boosted air from traveling backwards and putting a reverse load on the tuyrbo when the throttle body is closed(foot off gas). Aftermarket ones usually are adjustable and blow the air out of the intake pipe quiker. also give you a choice of sounds.

 

ok cool, thanx for the info

 

If you dont have one, you get compressor surge, which happens to make your car sound like ----.

 

and break