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

[Draven]

yah, $320 is the price my local is charging, which seems to be pretty good

[Endless]

Just don't run one, dose it bro..

[ReQuieM]

How much difference is having the BOV on the TB side really going to make?

I was about to weld on one on the turbo side (for the added stealth factor) but I mean if its going to make that much difference then I'm sure I can make something to hide it on the TB side.

30psi etc: How does the AVO one work? the HKS SSQV I used to have was set up so the pressure in the pipe held the bov shut, so I couldn't see any physical way for it to leak. It needed vaccum in the second chamber to pullit open, which also had a spring to hold it shut. Is it the same with AVO?

Just trying to get my head around how it could be forced open...

[BigWorm]

$320!!!
Damn, I just picked up one of those GReddy Type R jobbies (the big arse suckers, 40mm piston, I have one on the 4A, BvD has one on his p00 grenade) for $150. It's second hand, but retail's something silly like 380 or so.
I just can't fathom spending over $200 on a fuckenwoosh valve....

[Norbie]

All BOV's are a simple piston which rely on a pressure differential to open. Equal pressure = spring holds it shut = no leaking. This is why I contend there is no difference in performance between any reasonably well constructed BOV, unless you're talking some massive single turbo setup with eleventy billion hp, in which case you might need to think about the outlet diameter.

Of course the value of having any BOV at all is highly debateable, but that's a discussion for another thread.