BOV question

[4g63lover]

aight i've seen some wierd set ups. whats up with people who has two blow-off valves. wht does this do? i know quite a bit about turbo but i dunt know what the purpose of having two blow-off valves on a single turbo set up. oh as i might add on the intake side only. two BOV's on intake side only not intake and turbo. so what is the purpose of this?

[94gntturbo219]

I see no porpose for a blow off valve on the intake side. Now did someone tell you this, or did you see with your own eyes there was a blow off valve on the intake side ( it wasn't misenterpreted for an intercooler pipe?) The reason I ask is because the porpose of a BOV as you know, is to vent boost on closed throttle. The diaphragm of the BOV is acted upon by suction when the throttle is open, and when closed, the excess boost pushes it open in order to vent, so I see no reason why one of these would be applied to the intake side of an engine. It will remain closed when the car is sucking in air, but even when you let off the throttle, it's not venting anything due to the fact there is no excess pressure.
The reason cars run 2 blow off valves is for high boost setups where one BOV may not vent all excess boost when the throttle plate is closed, consider it a precation sometimes. Some cars run rediculous boost ( usually around 30 lbs or more) and most BOV's aren't adequate at those levels, or are reaching their limits.

[DOHCstunr]

two bov's is a way to bridge the gap betwen very high boost and low to normal boost without compressor surge.

you could get a full on race bov to vent the pressure at 30 psi. but you wold have to keep the spring very stiff. well as should know. you aren't going to hit 30 psi on every gear. on the street, you might no thold the gear for as long, or demand too much boost. lets say you only hit 12 psi before a shift, or 6 even.
well at only 6 psi if your bov is set up with a super stiff spring, its not going to open enough at the low pressures to vent the compressed air. so you''ll get compresor surge.
two moderate set bov's will have the ability to vent all the boost at high pressures, but still vent at the low pressures as well.

[4g63lover]

<div class='quotetop'>QUOTE(94gntturbo219)</div><div class='quotemain'>I see no porpose for a blow off valve on the intake side. Now did someone tell you this, or did you see with your own eyes there was a blow off valve on the intake side ( it wasn't misenterpreted for an intercooler pipe?) The reason I ask is because the porpose of a BOV as you know, is to vent boost on closed throttle. The diaphragm of the BOV is acted upon by suction when the throttle is open, and when closed, the excess boost pushes it open in order to vent, so I see no reason why one of these would be applied to the intake side of an engine. It will remain closed when the car is sucking in air, but even when you let off the throttle, it's not venting anything due to the fact there is no excess pressure.
The reason cars run 2 blow off valves is for high boost setups where one BOV may not vent all excess boost when the throttle plate is closed, consider it a precation sometimes. Some cars run rediculous boost ( usually around 30 lbs or more) and most BOV's aren't adequate at those levels, or are reaching their limits.</div>

i meant intercooler pipe. i mean like you know after the throttle body. i saw it on super street on the 4-door 400 hp dc2 they covered

[low sittin 8g]

i wanna put 2 BOV's on my intake.. lol

[Lazarus]

but wouldn't the air pressure be distributed between teh 2 BOVs so instead of getting 15 psi on the one bov at shift wouldn't it be more like 10 on the low pressure and 5 on the high(harder spring)? still doesn't make any since unless your using a twin turbo setup which still you wouldn't need 2. sounds like rice to me

[4g63lover]

thaz what i said.. but i guess it does makes sense lots of ppl do it. my friend wit a evo rs juz did it also juz today too how ironic/

[DOHCstunr]

<div class='quotetop'>QUOTE(Lazarus)</div><div class='quotemain'>but wouldn't the air pressure be distributed between teh 2 BOVs so instead of getting 15 psi on the one bov at shift wouldn't it be more like 10 on the low pressure and 5 on the high(harder spring)? still doesn't make any since unless your using a twin turbo setup which still you wouldn't need 2. sounds like rice to me</div>

yeah i thought i explained it pretty well.
you wouldn't do this on a low pressure car. single,twin, tri, quad turbo's- doesn't even matter.

Its for high boost high airflow applications.

if i was running a monster turbo on a monster built engine only at the track, i would just get the most powerful bov i can find. one that doesn't leak at 25-40 psi. and set it accordingly.
cause at the drag strip every shift is going to be at full boost, so low boost pressure surge wouldn't be an issue. If this was my all drag strip car that the way it would go.

however. if i wanted to drive that same highly modded car on the street. and even though my max boost may be set at lets say 25 psi on the street for pump gas. when i am accelerating slow or at part throttle. that one super stiff bov is going to cause my turbo to surge. cause the boost level will be too low for the high boost bov to open and function properly.
the result? damaged thrust bearings, damaged or broken compressor wheel, i.e. F.U.B.A.R turbo.

However one option for me woulf be to run two streetable blow off valves.(like an hks super sequential that can't leak by design)
their combined strength would hold boost for high pressure applications.
they total passage area between the two bov's would be twice that of just one; therefore they would flow/vent twice the air for high airflow application.
the key here is that on the street i'm not going to hit 20- 30 psi on every shift. on the street i might hit 2 psi here, and 8 psi there, and even 20 psi on a part throttle shift. having two medium duty bov's will allow for pressure relief at low boost without the surge that IS associated with race only bov's

rice? i doubt it.

[sabzi5858]

smaller diameter diaphragm=less force trying to push it open, but less cross-sectional area to vent through, so less flow. can use a smaller spring because of less pressure, faster reacting because of less momentum.

big diameter diaphragm=more force applied on it for same pressure, need stronger spring to hold shut, slower reacting due to more momentum, but lets out a lot of air.

solution: multiple small bovs. each one acts independantly so they remain fast reacting, but can still vent a lot of air just because there's more of them.

indeed, twin bovs is not rice (i suppose it could be, but not just because it's dual bovs)

some people will run a big one and a small one. at high boost, both open, but at low boost, only the small one has time to open.

[seth98esT]

Yay sabzi is back 8)

[DOHCstunr]

Yay sabzi is back 8)

HOORAY

[sabzi5858]

lol sorry, won't really be checking in very frequently, i decided to get serious with school and it's killing me. but you know where to find me if you need anything

btw seth, i checked in the fastest galant post and didn't see your time on there! when is it coming??