mine has one (HKS racing BOV)...the BOV is open when the throttle plate is closed

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Butcher &raquo;</TD></TR><TR><TD CLASS="quote">to explain a bit further, the BOV really opens when pressure in the intake piping exceeds the pressure in the manifold </TD></TR></TABLE>

Which would be boost... That's also the same reason you can't BOV in neutral with a T3/T04... The turbo is too big and can't build boost at idle, therefore you can't blow off... With a little *** Eclipse turbo you can BOV in neutral because the turbo builds boost at idle....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Butcher &raquo;</TD></TR><TR><TD CLASS="quote">to explain a bit further, the BOV really opens when pressure in the intake piping exceeds the pressure in the manifold </TD></TR></TABLE>

Yep and remember the srping pressure in the BOV too.

so a 7lb spring would open the BOV when the piping pressure is 7psi more than the manifold.

When you have boost on WOT the boost down the 'senisng line' is equal to the charge pipe pressure, the srping ensures the BOV stays shut.

When you close throttle the vacc line sucks on the BOV diagphram or piston while the pressure in teh charge pipe pushes the BOV open aswell, the difference in these preesures has to be above 7psi to overcome a 7lb springs

If it leaks at idle you havent got it connected properly or need a better spring.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thad &raquo;</TD></TR><TR><TD CLASS="quote">hks owners run a check valve on the vac line so it only sees boost. therefore air only goes out. otherwise.... oh well.no filter, no big deal.</TD></TR></TABLE>

You can also run a check valve on the BOV itself. Since the BOV opens at idle, it can affect idle. Plus it's sucking in unfiltered air as others have pointed out.

So if you don't want to route your BOV into the pre-turbo intake, you can add a large check valve to the BOV instead of a filter. He's one example that works great. These particular valves are made for water filtration systems and can be found at any hardware store - they are very beefy and will not melt. They fit right onto most BOVs, like the 1G DSM, and can be held on with clamps and a small piece of radiator hose that acts as a coupling.




http://www.geocities.com/kilruf/bov.html

- Slater

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JonnyCoupe &raquo;</TD></TR><TR><TD CLASS="quote">

Yep and remember the srping pressure in the BOV too.

so a 7lb spring would open the BOV when the piping pressure is 7psi more than the manifold.
</TD></TR></TABLE>

That's what I was going to add, well said.

That means that when you're at idle, the pressure in the upper IC pipe is close to 14.7 psi absolute, and there is high vacuum in the manifold. It's very likely that the BOV would be open at idle.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
If it leaks at idle you havent got it connected properly or need a better spring.</TD></TR></TABLE>

I disagree, see above.

Stock DSM BOV's will be open at idle, as will the TurboXS RFL (even when adjusted properly), and the really good Tial BOV is open at idle too.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 4U2NV &raquo;</TD></TR><TR><TD CLASS="quote">

Which would be boost... That's also the same reason you can't BOV in neutral with a T3/T04... The turbo is too big and can't build boost at idle, therefore you can't blow off... With a little *** Eclipse turbo you can BOV in neutral because the turbo builds boost at idle.... </TD></TR></TABLE>

i'm not sure you understand how a bov works. the port on the diaphragm side of the chamber? that is connected to a vaccuum line (post throttle body). the purpose of this is so the vacuum in the manifold when the throttle plate closes assists the pressure in the charge pipes to overcome the force of the spring and open the valve. this is meant to allow the valve to open and close very quickly. if the vacuum port on the valve is just seeing boost, and no vacuum, the pressure in the charge pipes must overcome the force of the spring on it's own, which opens the valve slower, and only at higher boost pressures- which means you still have a decent pressure spike (~5-7psi) going back to the compressor. the bov NEEDS vacuum to be effective.

when there's positive pressure in the manifold, post TB, that pressure acts on the diaphragm side of the valve to help keep the valve closed. if you put a check valve there without any sort of bleed, the boost will remain in the diaphragm canister and further oppose the valve's opening between shifts, worsening the boost spike hitting your compressor wheel.


Modified by filthy scarecrow at 9:01 PM 12/23/2003

 

heh should i pick one of these filter things up i have the blitz bov anyways

 

ok on the filter since nobody else seems to run one, dont wanna spend money if its not neccesary

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by filthy scarecrow &raquo;</TD></TR><TR><TD CLASS="quote">

i'm not sure you understand how a bov works. the port on the diaphragm side of the chamber? that is connected to a vaccuum line (post throttle body). the purpose of this is so the vacuum in the manifold when the throttle plate closes assists the pressure in the charge pipes to overcome the force of the spring and open the valve. this is meant to allow the valve to open and close very quickly. if the vacuum port on the valve is just seeing boost, and no vacuum, the pressure in the charge pipes must overcome the force of the spring on it's own, which opens the valve slower, and only at higher boost pressures- which means you still have a decent pressure spike (~5-7psi) going back to the compressor. the bov NEEDS vacuum to be effective.

when there's positive pressure in the manifold, post TB, that pressure acts on the diaphragm side of the valve to help keep the valve closed. if you put a check valve there without any sort of bleed, the boost will remain in the diaphragm canister and further oppose the valve's opening between shifts, worsening the boost spike hitting your compressor wheel.


Modified by filthy scarecrow at 9:01 PM 12/23/2003</TD></TR></TABLE>

Exactly. BOV's need to see a vacuum signal for them to be effective and work properly. If they needed a check valve, they most likely would have one designed into them by the company, since it is them that puts in all the R&D

 

So fit a 15 lb spring simple really.

Those filters are just to change the sound! not filter the air going in.

If the IC piping is at atmospheric pressure then why on earth would any air be inclined to go through the DV? Theres no pressure differential, unlless you have a REALLY dirty airfilter.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JonnyCoupe &raquo;</TD></TR><TR><TD CLASS="quote">So fit a 15 lb spring simple really.</TD></TR></TABLE>

I don't know, that's a pretty solid spring... I don't think I would want to run one that stiff.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
If the IC piping is at atmospheric pressure then why on earth would any air be inclined to go through the DV? Theres no pressure differential, unlless you have a REALLY dirty airfilter.</TD></TR></TABLE>

Simple answer: the upper IC pipe is not at atmospheric pressure.

The air has to get pulled throguh the intercooler and turbo, and the air filter.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by kpt4321 &raquo;</TD></TR><TR><TD CLASS="quote">

That's what I was going to add, well said.

That means that when you're at idle, the pressure in the upper IC pipe is close to 14.7 psi absolute, and there is high vacuum in the manifold. It's very likely that the BOV would be open at idle.

</TD></TR></TABLE>

You made your mind up yet as to what the pressure is?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JonnyCoupe &raquo;</TD></TR><TR><TD CLASS="quote">

You made your mind up yet as to what the pressure is?

</TD></TR></TABLE>

is this seriously that difficult?

read both his posts. they're both explanations of different things..

like he said, when you're at x psi boost and you slam the throttle plate closed, there is plenty of pressure differential. when you're at idle and the turbo is not spooled, the IC pipes are at atmospheric.

i cannot believe there's this much misconception about the operation of something so simple..

 

We are talking about idle here, and whether the DV leaks or not So both post are on teh same thing. WHICH IT SHOULDNT.

Loads of cars have Mass airflow sensors so any sort of unmetered air will completely screw up the engine running.

The pressure question i stated was a rhetorical queation, if you had read the WHOLE thread you would have see how the guy was contradicting himself?

Get it? 'i cannot believe there's this much misconception'

People need to start thinking rather than reading stuff they see on the net or hear off their mates.

 

this has got to be the worst logically argued thread i've seen on ht since i joined.

what's a bov for anyway...to releave pressure when the throttle plate is closed to keep from the pressure wave from hitting back into the compressor wheel. what happens when you let off the gas and the throttle plate closes...vacuum and the bov opens releaving that pressure from the chargepipe. boost pressure closes it and vacuum opens it. therefore when you are cruising in vacuum it is open and sucking air in there as well just like it was the filter at the end of your intake. i've acutally looked at my bov through the vent opening and it is open during idle/vacuum. filter it or not, but think about not having a filter on the end of your intake and what it'll suck into your engine. how many of you have dirt/dust in your engine bay? that's going into your cylinders...yay!!!

i recommend filtering it. i put a small k&n on mine at day one. cheaper and easier and way less of a headache trying to follow what everyone is posting here saying to the contrary.

 

You dont make boost at idle though.

So the purpose of dumping boost when the Throttle plate is closed is required.

Personally if my BOV leaked at idle i'd sort it out. Each to their own i guess.

Boost doesnt close a DV at all either. Its the pressure differential; across the BOV diagrham that open and closes it, depending if the pressure is higher or lower than the spring rating.

Its not as simple as Vac opens and boost closes.

I cant ever remembering having such a stupid thread on ANY UK forum.....

BOVS SHOULD NOT LEAK AT IDLE

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">Its not as simple as Vac opens and boost closes.

</TD></TR></TABLE>

yes, it is!

Boost closes the DV because there is equal pressure in the intake manifold and charge pipe, so the boost signal from the manifold that is being sent to the DV is equal to the one in the charge pipe. When the TB closes, there is an immediate VACUUM in the manifold, and that VACUUM signal is the same one that goes to the DV, which opens it in conjunction with the boost to vent the charge pipe. If you have no vacuum signal to the DV, there must be sufficient boost to manually force open the piston/diaphragm and vent, and if that pressure is not created, then you will get compressor surge.

DV/BOVs are open at idle because of the signal they are receiving, simple as that. They are not "leaking", as that would imply some sort of problem when they are actually working correctly.

 

Oh dear.

It doenst have something to do with the boost pressure exceeding the spring rating then when there vac, Cos when there is boost in the manifold too the pressures from the air are equal and its the spring which keeps it clamped shut.

At idle the spring should still keep it clamped shut. ENd OF

I pity all the guy with leaking DV its not good, ive seen very few manufacturers have BOV with filters... i guess they weren't designed to leak at idle.

Mind you Im being told how they work from people who fit rediculously high pressure fuel regualtors and call them 'Fuel Management Units'

GET A FOOKING BETTER SPRING!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JonnyCoupe &raquo;</TD></TR><TR><TD CLASS="quote">Loads of cars have Mass airflow sensors so any sort of unmetered air will completely screw up the engine running.</TD></TR></TABLE>

yes, and on cars with airflow meters, the air blown off between shifts is routed back into the system, post AFM. when the valve opens during vacuum conditions (which MOST OEM valves are DESIGNED to do), it's pulling air in POST AFM! this does not affect the mixtures in the least. in fact, it helps with off boost driveability as the engine no longer has to pull air across the compressor to get it into the engine.


<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JonnyCoupe &raquo;</TD></TR><TR><TD CLASS="quote">
BOVS SHOULD NOT LEAK AT IDLE</TD></TR></TABLE>

yes they should. i've explained it above. go grab ANY aftermarket bov and apply 20" of vacuum to it. it will open. the spring rate has to be kept rather soft in order to make sure the valve can open/close fast enough. if you have boost on one side of the valve, pushing on the diaphragm, and boost on the other side from the manifold, there is zero pressure differential, thus the spring holds it shut. when there is boost on one side of the valve and vacuum on the other (when the TB closes and cuts off airflow), the vacuum on the manifold side assists the boost on the charge pipe side of the valve in opening it against the spring pressure. the faster the valve opens, the less compressor surge you get and the faster it closes the sooner you're back at boost. vacuum is necessary to make sure it operates quickly enough.

some valves use very soft springs as well. the oem valve on the toyota MR2 turbo is a twin chamber type- the type many aftermarket companies copied for their designs (apex, HKS and greddy to name a few). it uses two chambers with the one that sees vacuum being larger than the one that only sees boost. under boost, the pressure in the larger chamber exerts more force on the valve than the pressure in the smaller chamber (even though they're at the same pressure, the larger area will always exert more force (if pressure is constant and area increases, so does force). this means that no matter what boost pressure you are at, the valve will always be held shut by boost pressure. the OEM MR2 valve can hold over 30psi without leaking, yet it opens quite readily at idle.

if you've not seen a "stupid discussion" like this one on the UK boards, perhaps it is because they all subscribe to a misinformed point of view. maybe it's time for you to have a "stupid discussion" like this one over there...

cheers.

 

bov isn't leaking at idle if it's opened slightly it's sucking in air just like an intake would. granted it's not open very far, but it is slightly open at idle. take a look at a bov not installed and it'll be closed. put boost pressure on it and it stays closed. put 20 vac on it and it'll open. when you are cruising/idle you will be in vac and that will be enough to crack it open and it'll stay cracked open until the vac is reduced on the line going to it. as you put more load on the engine the bov goes from being slightly cracked open to closed.

maybe mine is just seriously f#cked up, but it runs fine and hold plenty of boost.

 

Good god, think about this for a minute. If the BOV opens with boost, as soon as you get on the throttle and start making boost, the BOV opens and starts to bleed off boost, then when you let off throttle and the motor is running under vacuum the BOV would close, totally defeating the purpose of a bov and causing compressor stall.

About the original topic, yes, my bovs are open at idle, but when I put my hand by them the turbos are still spinning enough that a bit of air is pushed out, none is sucked in.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted92 &raquo;</TD></TR><TR><TD CLASS="quote">Good god, think about this for a minute. If the BOV opens with boost, as soon as you get on the throttle and start making boost, the BOV opens and starts to bleed off boost, then when you let off throttle and the motor is running under vacuum the BOV would close, totally defeating the purpose of a bov and causing compressor stall.
.</TD></TR></TABLE>

um.. what the hell are you talking about? where did i ever say the bov opens with boost? boost (especially in a twin-chamber design) is what holds it closed. vacuum is what opens it (we're talking about ONLY the pressure at the vacuum port on the valve here).. i've been stating this ever since my first post in this thread. this is how they work. it's simple really. maybe my explanation of it was confusing, but it makes perfect sense to me.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by boosted92 &raquo;</TD></TR><TR><TD CLASS="quote">
About the original topic, yes, my bovs are open at idle, but when I put my hand by them the turbos are still spinning enough that a bit of air is pushed out, none is sucked in.</TD></TR></TABLE>


No, air is sucked in. Wrong=bad.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JonnyCoupe &raquo;</TD></TR><TR><TD CLASS="quote">
You made your mind up yet as to what the pressure is?
</TD></TR></TABLE>


I figured you would understand English, since it's named after the country where you live, but apparently that is not the case.

First of all, what ******* pressure should I make up my mind about? We've been talking about all kind of pressures here (pressure in the intercooler pipe, boost pressure, spring pressure, pressure differential). They certainly aren't all the same, are they? As such, my numbers aren't all going to be the same, are they? NO. STFU.

In order to keep your BOV shut at idle you would need to run a 15 psi spring, or maybe even more (depends on the vehicle). I personally wouldn't want to run a spring that stiff, because it delays the amount of time that it takes for the BOV to open, which increases the possibility of compressor surge.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by filthy scarecrow &raquo;</TD></TR><TR><TD CLASS="quote">

yes, and on cars with airflow meters, the air blown off between shifts is routed back into the system, post AFM. when the valve opens during vacuum conditions (which MOST OEM valves are DESIGNED to do), it's pulling air in POST AFM! this does not affect the mixtures in the least.</TD></TR></TABLE>

POST meaning after? If your ingesting air after the AFM then it WILL ***** the ECU fuelling.