Correct me if I am wrong but the BOV will be open at closed throttle so it will be pulling in air through the valve until boost because the vacuum will be opening the valve? Im dont know if I am thinking about it right...


3400 SWAP DONE. 187WHP 212TQ (14.2 @100MPH NA) 240WHP 310TQ (N2O)

no. BOV should never be taking air in... otherwise its unfiltered air. TB closes, air goes out, once the pressure is released, the bov closes. Even when the TB is fully closed, air still passes through... hence the car running at idle.

a bov needs to be adjusted to prevent this. during normal engine idle the vehicle should have ~20 inhg(vacuum). when closing the throttle under boost the intake vacuum can reach 25-30inhg. in order to prevent your bov from opening under normal idle vacuum you want to adjust the bov when idling. turn the adjustment counter clockwise until the valve opens and then turn the adjustment clockwise until the valve closes. this will keep the valve closed at idle vacuum but open the valve when the throttle is closed during boost.

if you dont have a bov with an adjuster then you need to change springs until you achieve this.


make sure you dont use a by-pass valve as a bov as they are designed to open up under very little vacuum.

hmm my guage only shows i have 10 at idle

so just idling, the bov should not be open at all? mine is open and pushing air out but as soon as i give it throttle it closes, i thought thats how it was supposed to be?

JOE L wrote:

make sure you dont use a by-pass valve as a bov as they are designed to open up under very little vacuum.

then why do a lot of factory turbo cars have BPV's?..................... a BPV is just a recirculating BOV....

because a bypass valve or recirc valve is designed to re-route the bypassed air(boost) back into the turbo inlet because its metered by the maf. they dont have very heavy spring pressure like a bov. 1-2 inhg and they open.

jason norwood wrote:hmm my guage only shows i have 10 at idle

check for vacuum leaks or make sure your using a dedicated vacuum port. some ports are restricted at idle.

cody allison wrote:so just idling, the bov should not be open at all? mine is open and pushing air out but as soon as i give it throttle it closes, i thought thats how it was supposed to be?

your bov should not be open unless your throttle closed under boost which creates a spike in vacuum in excess of 20 inhg. you dont want to suck air into the bov.

your bov closes briefly when you open the throttle because you lose vacuum but a second later vacuum comes back and your bov opens. this is not correct. your creating lag. your turbo will take longer to spool up because your venting the air its trying to create boost with.

if your bov opens with little vacuum then its not a bov, its a recirc/bypass valve.

JOE L wrote:because a bypass valve or recirc valve is designed to re-route the bypassed air(boost) back into the turbo inlet because its metered by the maf. they dont have very heavy spring pressure like a bov. 1-2 inhg and they open.

i know plenty of non MAF'd cars that run bpv's and they work perfect. no issues what so ever. it all depends on the setup and how its done.

mine isn't sucking in air. its blowing out air

BuiltNBoosted wrote:

JOE L wrote:because a bypass valve or recirc valve is designed to re-route the bypassed air(boost) back into the turbo inlet because its metered by the maf. they dont have very heavy spring pressure like a bov. 1-2 inhg and they open.

i know plenty of non MAF'd cars that run bpv's and they work perfect. no issues what so ever. it all depends on the setup and how its done.

i never said they wouldnt work. i just said there not designed to be used as a bov. if the recirc valve is open all the time there is vacuum to it then your sucking in outside unfiltered air and your creating lag.

cody allison wrote:mine isn't sucking in air. its blowing out air

if your valve is open during idle then it is sucking in air. if its not open during idle then most likely you have a bov with a heavier spring instead of a recirc valve with a lighter spring.

hmmm what does a bov do? relieves excess pressure from the charge pipe once the tb closes...
hmmm what does a bpv do? relieves excess pressure from the charge pipe once the tb closes...

BuiltNBoosted wrote:hmmm what does a bov do? relieves excess pressure from the charge pipe once the tb closes...
hmmm what does a bpv do? relieves excess pressure from the charge pipe once the tb closes...

thats correct. a bov relieves excess boost pressure when the throttle body is closed. it also prevents boost from pushing open the bov. a properly woring bov should not be open at normal idle vacuum.

Thanks for all the info, I am still putting the final pieces on and was hooking up the BOV and was just wondering about the function at idle. Im not sure if mine is adjustable.


3400 SWAP DONE. 187WHP 212TQ (14.2 @100MPH NA) 240WHP 310TQ (N2O)