I have two questions. Does anyone know if the 2001 Volvo S40 1.9t already has a Blow Off Valve on it stock. And my other question is if there is a stock BOV already on it, do I have to take that one off first before i put an aftermarket one on?

Wow...does anyone know anyhting on this forum? HELPPPPPP!!!!

firstly, we know lots. second, we are not only on this forum to answer things, we have to work you know. now to your question, yes there is, but not like the one that you want. volvo owners, the typical older ones, don't want to hear the blow valve, so the stock one is reeeaaaaaaaally quiet, now why do you want to change the valve? have you done any mods to the engine? and i don't count filter and plugs as mods. if you haven't, you don't need to change the valve, no reason to waste your money. it won't creat any power. start changing things, then you change the valve.

What upgrades do you think I should make to the engine in which installing a new BOV will be significant. I am mostly wanting to get one for the sound, thats it.

AMEN!

the sound is just that, sound. go for a good quality down pipe and exhaust. an open filter, k & n, for example. the plugs, wires, rotors, etc. just that alone will jump your power output. now, to do it correctly, start with those, then the brakes, suspension, then, you go for the good stuff. chips and a reprogram. larger turbo, intercooler, etc. then the blow-by valve is needed. if you got the dosh and just want the sound, buy a slightly upgraded blow-valve, remove the old one and install the new one. that way you'll hear the whoosh. you won't be any faster, just getting to the stock pressure faster. no speed. hope that helps. don't want to sound like a pain the a*&, but do it right the first time and you'll enjoy your car more.