When do you need a BOV???

[WELTERRACER]

Is it only necessary when you add a intercooler or is it the PSI that determines when you need a BLow Off Valve??

[protour_chevelle]

You need one in order to bleed exess pressures in your charge pipes when letting off of the throttle.

[WELTERRACER]

I know that.. My question is when do you need it? When you add a intercooler (or only if you get above a certain PSI)

I havent used in at all in the last 2 years but im below 10psi... I am thinking of adding a intercooler ... and am wondering if i really need one..

[camcojb]

I know that.. My question is when do you need it? When you add a intercooler (or only if you get above a certain PSI)

I havent used in at all in the last 2 years but im below 10psi... I am thinking of adding a intercooler ... and am wondering if i really need one..

you should always use one.

Jody

[homerneedspeed]

you don't Have to have one. if you don't use a BOV it will make the wastegate flutter and the car will sound like a WRC rally car. i have a few friends that have ran WRXs, dsms and Evos for tens of thousands of miles and years with no ill effects so far.

[camcojb]

you don't Have to have one. if you don't use a BOV it will make the wastegate flutter and the car will sound like a WRC rally car. i have a few friends that have ran WRXs, dsms and Evos for tens of thousands of miles and years with no ill effects so far.

well, he doesn't have a wastegate. With a centrifugal you need the bypass valve period or you will damage the blower at some point.

Jody

[Blown353]

If you are asking about your application (centrifugal supercharger) you need a *bypass valve*, not a blowoff valve. Two entirely different things. Running a BOV on your centrifugal blower will load it at cruise/vacuum conditions (since the BOV will be closed) and put undue wear on the supercharger.

A blowoff valve only opens when there is a pressure differential across the throttle plates and intake plumbing (i.e. it only opens when it sees positive pressure in the intake piping and vacuum behind the throttle body) whereas a bypass valve is open at all times as long as there is vacuum behind the throttle plates. Since a supercharger is always spinning as a proportion of engine RPM and trying to move air you want the bypass valve to be open at all light load conditions-- a blowoff valve won't do that.

[camcojb]

If you are asking about your application (centrifugal supercharger) you need a *bypass valve*, not a blowoff valve. Two entirely different things. Running a BOV on your centrifugal blower will load it at cruise/vacuum conditions (since the BOV will be closed) and put undue wear on the supercharger.

A blowoff valve only opens when there is a pressure differential across the throttle plates and intake plumbing (i.e. it only opens when it sees positive pressure in the intake piping and vacuum behind the throttle body) whereas a bypass valve is open at all times as long as there is vacuum behind the throttle plates. Since a supercharger is always spinning as a proportion of engine RPM and trying to move air you want the bypass valve to be open at all light load conditions-- a blowoff valve won't do that.

Yes, I assumed he meant bypass valve.

Jody

[Twin_Turbo]

a blow off valve is needed when you have situations where the throttle plates are slamemd shut, yet the compressor is still spooled up, like shifting w/ a manual box. Then you need to bleed off the pressure before it can damage the compresor wheel.

[blown69nova]

A bypass valve is used to recirculate air back into your air filter/maf and a blow off valve simply bleed the air into the atmosphere when the throttle plate is slammed shut. I would use one any time your use boost. If your motor sees 8psi when the throttle is open, imagine what the pressure spikes to when the throttle slams shut at 6000 rpm!
Steve