BOV sizes

[Draven]

I went to place an order for a turbosmart BOV, and realised that I have no idea what size I'll need.... can someone help out?

it'll be a plumb back, and has to deal with ~400rwkw/22psi. Ideally I'd like to go as quiet as humanly possible (but am assuming a little 22mm job will not be up to the task)

[Vios-GT_07]

i'd say go for this..

FG-BOV-003PB32 – (32mm outlet), FG-BOV-003PB34 – (34mm outlet),

but don't quote me on that.. it's 22psi eh.. a mate suggested 34mm would be alright for it.. a bit on the big side which would give you a bit more room for higher boost ..

*waits for second opinion to be proven right / wrong

[Norbie]

IMO it will make two fifths of fuck-all difference.

[tyottsoarer]

Vented air is vented air. I agree with norbie unless you're dealing with a Bov with a pin prick outlet. I'm running 22 psi through one of those purple trust type R ones and i cant hear any flutter

[Vios-GT_07]

IMO it will make two fifths of fuck-all difference.

that did cross my mind.. then i wondered if it's a specific thing that looks at boost pressure and volume.. assuming that it's going into a bigger motor like a 7M or something with a big ass T-3/4 sized turbo..

why would turbosmart make so many sizes (4?) for one plumb-back type BOV.. ?

[Draven]

my main thought was: will there be a difference in noise depending on size? higher velocity for the 22mm, probably greater volume for the 38mm

[30psi 4agte]

A bigger valve will alow more air/pressure to escape quicker .This will keep the turbo( compressor) spinning faster and hence due to a bigger valve there is less pressure (in IC pipes) / reversion caused by the throttle flap closing causing the compressor to slow.

This will cut down on respool time of the turbo charger between gear changes .

I would go with a big valve or 2 of the smaller ones .

Using a big turbo like you have you will benifit from a bigger valve
m8.

I use to use 2 blowoff valves but then went to the 50mm AVO one i have now. This change was not based around a flow issue as the two smaller valves provided enough flow but was due to the fact that the valves i was using could not handle the boost and were being forced open and causing problems when trying to setup the boost controller

22 psi is a decent amount of boost so you should consider or atleast ask the question when you decide on which valve you choose.
is it able to hold that amount of boost without leaking / creeping?

[30psi 4agte]

my main thought was: will there be a difference in noise depending on size? higher velocity for the 22mm, probably greater volume for the 38mm

ahhh knew i forgot something!

In my opinion a larger valve is quietr
Velocity will be louder than volume

[1jzracing]

A bigger valve will alow more air/pressure to escape quicker .This will keep the turbo( compressor) spinning faster and hence due to a bigger valve there is less pressure (in IC pipes) / reversion caused by the throttle flap closing causing the compressor to slow.

This will cut down on respool time of the turbo charger between gear changes .

I would go with a big valve or 2 of the smaller ones .

Using a big turbo like you have you will benifit from a bigger valve
m8.

I use to use 2 blowoff valves but then went to the 50mm AVO one i have now. This change was not based around a flow issue as the two smaller valves provided enough flow but was due to the fact that the valves i was using could not handle the boost and were being forced open and causing problems when trying to setup the boost controller

22 psi is a decent amount of boost so you should consider or atleast ask the question when you decide on which valve you choose.
is it able to hold that amount of boost without leaking / creeping?

i agree totally ... i use 2 also one on each side of the IC and theres hardly any noise

what i CANT understand is how can blow off valves blow open?? the pressure pushing it open is matched by the same pressure on top pushing it closed plus the spring also pushing it closed so they will always stay shut, unless the throttle is partly or fully closed in that case you want it open!

[30psi 4agte]

yep i know what you mean. But i assure you i was right next to my car on the dyno with my hand over the valve and could feel the air!

I think it mabe due to the pressure vs area issue. Ie there is a larger area of pressure acting on the valve diameter(valve seat) pushing it open then there is in the diaphram pushing it closed.

Same goes for an external waste gate

[EVOSTi]

i have a tial BOV, its damn huge but not plumb back. probably too big for my little 4a cause i get surge at anything under 15psi, byt hey it was cheap at the time.
apparently these BOV's are pretty popular with the drag racing boys in the US? must be ok.

[Norbie]

A BOV will typically leak at WOT when there is a restriction somewhere in the inlet system. For example you could be seeing 12psi at the plenum, but there's a pressure drop of 3psi across the intercooler, so the turbo is actually pushing 15psi. That means there will be a 3psi pressure differential on either side of the BOV, which might be enough to make it open a bit.

[Mr Ed]

A BOV will typically leak at WOT when there is a restriction somewhere in the inlet system. For example you could be seeing 12psi at the plenum, but there's a pressure drop of 3psi across the intercooler, so the turbo is actually pushing 15psi. That means there will be a 3psi pressure differential on either side of the BOV, which might be enough to make it open a bit.

This is why a BOV should be placed on the TB side of the IC.

[Draven]

right.. so basically I'll get the 38mm.
pretty much what I thought, but good to be sure

[ganador]

Plumb backs dont usally create much noise anyway. the best for you would be a Turbosmart Plumback sleeper series FG-BOV-003PB38-S it will kope with the power you have very nicly without much noise. Youll be looking at around $320 - $340 for one of these