How o BOV works on our cars.

Here is some info that i got on a BOV after this guy told me not to use one on my s-12.
I questioned him on it because i did not uderstand when he said i couls LOOSE power with one.
now that it has been explained it seems logical.
look like my sleeper status just increased a bit more.

Side note:
this guy (cam) owns a performance shop here in alberta and he does know his stuff when it comes to FI. and check out our forum out here lots of good guys and a great community!

http://www.albertacars.net/forums/showthread.php?t=369
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www.impressionsauto.com

yes, what he said was true. But it is a very good idea to use a reciculating valve, OR you can find a BOV that vents to atmosphere that also has a spring behind the diaphram (usually called, "adjustable BOV" or something of that nature). These BOV's will only open when you shift, not when your at idle if adjusted correctly (because of the spring pressure). Thus, only allowing you to lose air out of the post-maf system (aka run rich) for a split second. All said, I would still run a circuilating valve over a BOV on our cars, but I am just pointing out the other side to the story.
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Jeff Hester
1986 200sx 2.0L
1967 El Camino 402ci

i got a apexi twin chamber adjustable bov, and it works great on our application.
one room will collect the air and keep it so when you shift you don't even have to run rich because you got the air of the second room for a split second but i still vent and still the loud ass noise is heard.
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Well i got a '87 200sx (ca18et) totally stock now and looking to move up.
I am from originally from Albania(crazy mothers i know) but i wanna a '87 car to smoke some riced up new stuff, and the good of drifting

I'm now running a 1G DSM recirculating BOV off a first gen Talon/Eclipse (hence the 1G)
My atmospheric BOV just started losing peak boost. When first installed, it didn't leak at idle, held to 16 psi and was nice and loud, without having that air-brake release sound. But then it started only holding 14, then 12, then finally 10 psi and was leaking on idle. After checking everything else, and almost giving up on my turbo, I went to the 1G. Back up to 15 psi, no stumbling, no fuss and that nice "refined" DSM sound.
A BOV isn't really a performance mod, so much as it is prevention. I found at my boost levels, the BOV did make the car faster. It used to get pretty stuffed up by the top of 2nd gear without a BOV at all.
But without one, at increased boost, you're putting a lot of unnecessary stress on your turbo.
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1987 200sx CA18ETi
1972 Dodge Charger 413ci/6.6L
1968 Mercury Cougar 289ci/4.6L ForSale
Matt Lamperd
http://www.angelfire.com/freak/brutesquad/index.html

BOV is for ppl who are lazy to shift a turbo car and it is when you shift slow. When a really fast throw occurs you WILL NOT hear the sound and bov doesn't do much at that time since when you shift in a split second the turbo doesn't have stress applied upon therefore no need to vent since it's one constinues motion
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Well i got a '87 200sx (ca18et) totally stock now and looking to move up.
I am from originally from Albania(crazy mothers i know) but i wanna a '87 car to smoke some riced up new stuff, and the good of drifting

ahh negative when you have a turbo that can flow 400-500cfm it doesnt matter how fast you shift you will create a shockwave that bounces back and hits the compressor blade.. the bov prevents this and will vent even if it sees vac for a split second.. bov are for people who want to keep their turbos alive not thos who cant shift fast...
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

I only got a BOV for the noise that it makes. I not ashamed to admit it, I rang the mail order compay and just asked for the loudest one!
That sound makes me smile every time I hear it (even more when I make other people hear it icon_rolleyes.gif )

I was advised when getting one that although cheaper BOV's that use diaphrams can cause bother such as letting air in at idle and leaking at high boost. But I see people here using them so they cant be all bad.
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ALL NEW PICS HERE!
http://www.cardomain.com/member_pages/view_page.pl?page_id=382417

SEE MY MATE'S CAR @
http://mazda.p7.org.uk/porsche%20web/index.htm

i'm currently hunting ebay for a bov (or a recirc) as the mazda recirc valve i have only holds to 8 psi. anyone have any good recommendations for what to look out for?

1G BOV will hold up to ~20psi uncrushed. Crushed, the sky is the limit.

But it still has a nice *psssht* sound. I got mine for $30 used.

And if you're not hearing your BOV at high RPMs, it's because it's leaking. I can hear mine just fine at 7,000 rpm and 16psi. If your BOV is leaking at high boost, you're destroying your turbo. If the boost gauge is registering 15 psi with a leaking BOV, the turbo is working as hard as if you had the wastegate unhooked.

The problem has nothing to do with speed ... and it is 100 times more important on our cars, as when our throttle is closed, there is no bleed at all.

When the throttle closes, the boost comes back at the turbo. The turbo is still trying to spool, so it's compressing the air in between the turbo and the TB. With only a bit of pressure on the compressor side, and a whole bunch on the output side, the turbo can stall. This is brutal for your turbo. These things are spinning at an unreal rate, and coming to a dead stop is murder. Even if only for a fraction of a second, you're doing a bad thing.
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1987 200sx CA18ETi
1972 Dodge Charger 413ci/6.6L
1968 Mercury Cougar 289ci/4.6L ForSale
Matt Lamperd
http://www.angelfire.com/freak/brutesquad/index.html

so f1 lamans, and sl other racing applications that use bov's are people who can shift wotrth shit huh... i beg to differ
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

my first recomendation for a BOV would be a 1g DSM unit. stay away from the 2g units. (2nd generation started in '95) They work like a charm, have a nice "refined" icon_biggrin.gif sound and really get the job done. You'll have to do alittle welding and plumbing, but its well worth it.
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Jeff Hester
1986 200sx 2.0L
1967 El Camino 402ci

hell for 80 bucks you can get the huge puppy i got thats fully adjustable nice and loud and can hold up to 45psi.. well worth every penny
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

Most BOVs release when they see a change of roughly 7psi (postive pressure or positve to negative pressure). i.e. you can only have 4psi of boost, but if you completely let off the gas and let it reach a vacuum state, it will blow off the excess pressure if a change of 7psi is seen... same with say 12psi down to 5psi, it will blow off dispite still creating boost.

Like the others said, the point in a BOV/recirc is to vent the shockwave pressure that is created when you let off the throttle to shift and the throttle body slaps closed... the rush of intake air now backs up and surges in the other direction, causing compressor surge... basically the turbo momentarily halts its spin due to the back surge of air pressure and then attempts to spin correctly again (being pushed by the exhaust flow) and its causes a struggle back and force (exhaust flow wins of course, but the intake back surge is only slightly weaker), quickly causing wear on the turbo shaft...

For an example, hold out your hand fingers out, palm down, and kinda turn your hand slowly in a clockwise direction and shake it a little counterclockwise as you go, back and forth, but continuing in a clockwise direction... you'll get the idea.

Most say if you go with an atmospheric BOV it will cause increased lag as you loose that air that had been pushed forward, but in actuality the turbine keeps spinning and will quickly ramp back up once you get on the throttle. The only real issue with it is it causes an air/fuel imbalance... the MAF and ECU have already measured the air you just vented... and it goes "missing" when vented to the atmosphere... the ECU doesn't know this and adds the fuel for the air it metered anyway, causing a rather rich moment... by recirculating it... the air never goes "missing". Something to think about. I like it vented myself (just for the noise), but to each his own.
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KaZ

'84 S12 CA18ETi T28 200SX HB
'91 Z32 VG30DETT Fairlady Z
'91 Z32 [ Missing ] Fairlady Z (For Sale)
'97 A32 VQ30DE Maxima SE

i think i must be the only guy who wants a quiet bov icon_biggrin.gif guess i'm just old.

i know this is completely the wrong mindset, but i hate to dump a hundred dollar bov in a car that i paid $400 for. so i'm looking for a cheap (but decent) solution.

i'll see if i can locate a 1st gen dsm valve. are they good for 15psi? the mazda valve i have is supposed to be good for 15psi but leaks after 8. (maybe i'll take it apart and see what's up).

1g dsms are good for more than 15 psi. uncrushed they are probibly good for atleast 20. Crushed, who knows, probibly more than the stock ca18et bottom end will take.
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Jeff Hester
1986 200sx 2.0L
1967 El Camino 402ci

what does crushing refer to exactly?

My hks ssqv BOV has worked like a charm since I got it almost 2 years ago. Nice very high pitch squeal when it vents. Gets peoples attention every shift.
I had an Apexi twin chamber bov before the hks one, and it did nothing but leak under boost. I thoght the sound was very boring too..........sounded like a school bus releasing it's air brakes. Nothing exciting at all.
Anyway took it back to the shop where I got it and they let me exchange it for the hks one. The Apexi one ended up being defective.....Piece of shizit.............Euroboy, if your not having any problems with yours, looks like you got lucky, as i've been told by different sources they are known for leaking. Keep an eye on it.
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Keith
'84 S12 Turbo
'95 A32

HKS is what I'll be getting for my 200SX when I install the intercooler...
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KaZ

'84 S12 CA18ETi T28 200SX HB
'91 Z32 VG30DETT Fairlady Z
'91 Z32 [ Missing ] Fairlady Z (For Sale)
'97 A32 VQ30DE Maxima SE

so then why do lemans cars with turbos with paddle shift that shift the gearbox in .3-.5seconds or less still use a bov and why can you still hear them.....partially open or fully closed there will always be a shockwave that gets created and thrown back onto the compressor wheel
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

ding... its a pressure change... as long as there is enough of a variance from one side of the valve to the other... its going to OPEN!! Hence the noise. They will always open. On autos where you never take your foot off the gas, they're LESS audible, but still audible for some shifts, even with the throttle body open all the time. There is still a pressure drop when it shifts.
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KaZ
'84 200SX T28 Turbo Hatchback
'91 Fairlady Z - Version S (JDM nose to tail)
'91 Fairlady Z - Version S (For Sale)
'97 Maxima SE (For Sale)

I doubt too many people can shift faster than atmospheric change relative to a turbocharger spinning at 100,000 rpm then dropping to 10,000. There's a reason almost 100% of turbo cars come with some kind of a bypass valve from the factory.
It doesn't matter if you shift at the speed of light, it won't make any difference to your turbo.
If in 2nd gear at 15psi you shift into 3rd even without ever taking your foot off the gas, you're still going to have an unbalance. Just because the TB is open doesn't matter. If the engine can't use the boost, it doesn't just disappear. An engine under no load sure as hell doesn't need 15 psi of boost, nor can it use it. Your turbo has to work harder to overcome the 15psi of pressure that's now on the output side. This is what kills the turbo. The shockwave is just one factor. Spinning at different speeds has no effect on the lifespan of the turbo. Trying to spin at 2 different speeds at the same time is what damages it.
The BOV will eliminate the pressure on the output side, so you don't have anything pushing back against the turbo. As soon as the load is reduced on a motor, you stop making boost. Just revving your engine in neutral won't build boost. So as soon as your clutch goes in, load on the engine is reduced to almost nothing, and no boost will be generated. This is the start of the imbalance. When an engine is not under load, it doesn't need much fuel/air. So now you have 15 psi of boost on on one side of the turbo with nowhere to go, and maybe 1 psi of boost on the compressor side, regardless of RPM. So your engine and turbo now have to generate enough exhaust velocity to overpower what's sitting in the outpipes. Your spool is slow, your turbo is getting battered, and you're going slower.Whether it takes you a nanosecond or a minute to shift won't change that.
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1987 200sx CA18ETi
1972 Dodge Charger 413ci/6.6L
1968 Mercury Cougar 289ci/4.6L
Matt Lamperd
http://www.angelfire.com/freak/brutesquad/index.html

exactly.. i think we have slaved at whether the bov is valuable or not..... if professional race cars use them they must have a very crucial purpose...
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

because lemans cars run for 24hrs, and durability is in effect. All you said is true no argument here whatsoever but i am just trying to say that if you shift really fast on some drag competitions where turbos aren't going to be as reliable, they won't bother with BOV's due to the nature of the race they are doing. Mr.200 most ppl when they change realy fast and are precise about it change well under a second. So i have a question, why is it that when you shift slow you hear a sound and when shift really fast is no sound that i can hear. I am sure the pressure drop is there but it's so little sometimes it can be eleminated as a factor(only on special cases
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Well i got a '87 200sx (ca18et) totally stock now and looking to move up.
I am from originally from Albania(crazy mothers i know) but i wanna a '87 car to smoke some riced up new stuff, and the good of drifting

well drag cars use new motors very often so a bov isnt that big of a deal and trhe reason you dont hear your bov when you shift quick cause 1 you bov isnt loud enough 2 you engine is too loud or the interior to sound proofed
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

how much boost are you running? The factory 5 psi?
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1987 200sx CA18ETi
1972 Dodge Charger 413ci/6.6L
1968 Mercury Cougar 289ci/4.6L
Matt Lamperd
http://www.angelfire.com/freak/brutesquad/index.html

ohh good point matt cause you wont hear crap with the stock boost level
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2

no my friend in a volvo is boosting 20psi out of a t3 with an HKS bov that when you are outside you hear a huge ass sound, when he is racing : NOTHING: it's because not a lot of air is being vented out for a long time, there might be a tad of noise but never as it is when slow shifting takes place.
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Well i got a '87 200sx (ca18et) totally stock now and looking to move up.
I am from originally from Albania(crazy mothers i know) but i wanna a '87 car to smoke some riced up new stuff, and the good of drifting

it alos depends on how tight he has bov setup too...
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bart
'86 INTERCOOLED Turbo
1/4 mile: 14.964 @93.02mph
CEO of:
"Barts Parts Incorporated"
http://geocities.com/bartc_j
http://members.cardomain.com/bartc_2