twin turbo BOV question

[Santa'sBoostinSleigh]

yello again, i know its not directly toyota related, but meh

on a twin turbo setup (for example, v6 2.5L vr4 motor )
how does the BOV work? is there one BOV for each turbo or what?

these turbos are piddly little things btw!

[Ae92typeX]

bov works off vacume pressure in manifold, so you just have one for the twins.

[Santa'sBoostinSleigh]

yeah come to think about it and that that makes sense... sorry my bad

[matt dunn]

You can run two.

On our levin with the 1JZ twin turbo we had two pipes, one from each turbo too the intercooler and each pipe had a BOV on it.

Matt

[method]

bov works off vacume pressure in manifold, so you just have one for the twins.

No i always thought they work on pressure in the manifold. Most cars have vaccume pressure in the manifold.

When the throttle body shuts they air being rammed in by the spooled up turbo has nowhere to go, where does it go? Out into the atmosphere (or plumbed back into the intake before the turbo) hence the louder psssttt noise at higher revs

[vvega]

omfg
im speachless
method are you related to dr-x by any chance you seem to have one thing in comon

v

[Crimson Tears]

Aren't vacuum and pressure two completely different things?

[Ae92typeX]

bov works off vacume pressure in manifold, so you just have one for the twins.

No i always thought they work on pressure in the manifold. Most cars have vaccume pressure in the manifold.

When the throttle body shuts they air being rammed in by the spooled up turbo has nowhere to go, where does it go? Out into the atmosphere (or plumbed back into the intake before the turbo) hence the louder psssttt noise at higher revs

take a bov apart some time, you will see its a spring that pushes the piston inside closed. the vacume opens it and when vacume dissapears- e.g. when you put your foot back down after gear change the spring pushes it closed again. when you adjust a bov, you are adusting how much you put pressure on the spring and theirfore how much vacume it takes to open it up. less pressure, longer woosh, more pressure shorter one. To little and it ioens up when at idle anc causes bad running (airleak)

[fivebob]

I see the plentiful tech knowledge of Toyspeed abounds in this thread

You can run either one or two BOV's depending on how you do the plumbing. If the BOVs are placed before the line from the turbos join you would need to run at least two BOV's, if you place it after they merge then, depending on flow requirements, you can run just one BOV.

Twin BOV's are typically run where you have a separate I/C for each turbo, e.g. Ferrari 288GTO/F40, single BOV's often used where there is only on I/C e.g. Supra/GT-R

BTW BOV's work on the pressure differential between the manifold and the post turbo intake piping. When the manifold pressure is lower than the intake piping, and the difference between the manifold pressure and the pressure in the intake piping is greater than the force exerted by the spring in the BOV, then it opens.

Oh, and there is no real difference between pressure and vacuum. Vacuum is just pressure relative to atmospheric. Easier to use the metric system in which 101.35KPa is one atmosphere anything above that is boost and below that is vacuum, with 0KPa being absolute vacuum.

[shaggz]

im under the assumption that it is boost wich causes it to open if it runs on vaccuum in theory when yuor car is idieling would the valve not be open?????? as i understand it the valve is activated when you close the throttel(when yuo take yuor foot off the gas)the throttle snaps shut creating excessive pressure between the turbo and the throttle body so to prevent back pressure damaging the turbo and slowing spool up of the turbo the bov releases the air into the atmoshpere with a pedestrian violating pppppsssssssssshhhhhhhhhhh am i not right or am i very wrong,and the srping is in the valve to push the cylinder back down when yuo put your foot up it again and open the throttle to stop boost leak,

[fivebob]

am i not right or am i very wrong,and the srping is in the valve to push the cylinder back down when yuo put your foot up it again and open the throttle to stop boost leak,

A little of both

It's not the pressure that opens the valve, it's the pressure differential between the manifold and the intake piping, The reason some BOV's are not open at idle, is that the spring pressure is enough to overcome the difference between the manifold vacuum and the vacuum in the intake plumbing. However some BOV's (most notably, stock ones) do indeed open at idle because they use a very weak spring.

The spring pressure aids in the shutting of the valve but is not always the sole reason that the valve shuts, The stock Toyota valve also uses a device called a Vacuum Transmitting Valve (VTV) to create a pressure differential between two chambers separated by a diaphram, this aids in both the opening and closing of the valve. See This Thread for an explanation of how the stock Toyota BOV works

[Ae92typeX]

would you say a vacuume is just the lower of the two in a pressure differential then, or something different?
(I aint trying to argue anything, I dont know, Ive always reffered to it as a vacuume opperating the bov...incorrectly perhaps)
I was only refering to aftermarket bov's with springs only, not vtv

[Ae92typeX]

dont worry...just re-read about vacuume & pressure related to atmosphere properly in your post.

[vvega]

typically at higher rpm more vacum is generated so it is not uncomon for a bov to be open whilest decellerating though a gear or simply reving a engine

normally a bov is needed for each seperate intake system so if it has 2 pleums and two throttle bodys 2 are required to be the most effective

independant throttles feeding off a comon"airbox" do not require more than one

and yes there are positive pressure BOV's (comonly called pop valves)but there typically to stop overboost only not to prevent compresser surge unlike a differential presure BOV

v

[Santa'sBoostinSleigh]

just so you all know its spelt VACUUM!!!!

some of the spelling and grammar in here is getting shocking and makes everying so hard to read

END RANT

[Mr Revhead]

" "

[vvega]

just so you all know its spelt VACUUM!!!!

some of the spelling and grammar in here is getting shocking and makes everying so hard to read

END RANT

lol im over it
i guess i just cfb putting that extra effort in

v

[Santa'sBoostinSleigh]

wasnt aiming at you v, mainly at stephen, i mean hes gone retarded - went and traded in the toyota for a scoobie which he is going to blow up

[vvega]

lol yeah man subies all blow up
ash ewan
1 day and he bottom end fell out and that was one that had no mods at all.........
ej20's are almost the same as a bloddy rotary...or a 3sgte

v

[shaggz]

levin shagged gearbox,starlet,shaged almost everything,corolla shagged gearbox,hahahahahaha at least the scoobie sounds awesum,hahhaha besides paul was dumb enuf to by the levin nows its worse than a log of turd with wheels, and besides andy your mum loves the back seat of the scoobie,