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View Full Version : Blow Off Valve, Dump Valve, BOV



Ian C
03-04-05, 21:26
Name:
BOV

Also known as:
Blow Off Valve
Dump Valve

What is it?
When you take your foot off the accelerator to change gear or whatever there is suddenly a lot of pressurised air from the turbos that has nowhere to go as the throttle plate is shut. A BOV is a valve that is triggered by the pressure difference in the manifold and gets rid of this excess air. If this didn't happen it would cause the turbos to suddenly stop spinning, which would not only knacker them in short order but mean they had to spin up from a standstill when you got back on the throttle again.

There are two types of BOV, one vents the air to the atmosphere (atmospheric) and the other vents it back into the air intake (recirculating). The standard BOV is a recirculating job and is generally regarded to work fine up to around 18psi of boost. After this or when they get a bit old, they have been known to leak.

The main reason for changing to an aftermarket one is to make a nice loud whoosh when you back off the throttle as nearly all of them are the atmospheric type. Sometimes it’s out of necessity, such as with a single turbo conversion which removes all the stock BOV plumbing. You can mount them in the same place as the stock one (kits are available to do this for most BOVs), or have a flange welded to a hard pipe somewhere (typically the one that goes into the throttle body, but anywhere between turbo and throttle body is OK). You can also keep the stock one and add an aftermarket one as well.

Pros:
Makes a cool whoosh noise when you back off the throttle .
A well made one can hold more boost than the standard one without leaking.
In theory recirculating the hot pre-intercooled air back into the intake like the standard BOV could heat up the intake air whereas venting it does not but this is very unlikely to make any difference in practice.
Looks 'bling' under the bonnet.
A necessity with a single turbo conversion due to removing all the stock plumbing.

Cons:
If you have a UK car, an atmospheric BOV can confuse the ECU because they use a MAF airflow sensor which is ahead of the BOV. This sensor registers that a certain amount of air is flowing in, so the ECU reacts accordingly by supplying the correct amount of fuel. That air then gets vented by the BOV, so the engine runs very rich. This creates two problems – one, the car may stall if the throttle doesn’t come back on, two, if the throttle does come back on the ECU is trying to compensate for an over-richness and may lean the mix off to undesirable levels, potentially causing detonation.
The j spec cars have a manifold pressure sensor and don't suffer from this problem.

-Simon B

MarkTheBoy
14-06-06, 22:03
Hi all,

Just wondered if there is a guide available for fitting an aftermarket bov. I have just bought one from importpimp (nic) and am pretty sure that I could fit it but wanted to have some kind of instructions with pictures to make sure I don't cock it up :)

Any help would be appreciated, I've done a search but not really found anything helpful and the instructions that came with it are japanese...

Theres nothing else I need to do when fitting one is there regarding setup of the engine, turbos etc? I assume its just a straight swap.... Ish :think:

Cheers all

Daston
15-06-06, 12:47
Yeah would be usful as well as how to fit them on IC pipes for us lot who are going NA-T

supra sam
16-06-06, 16:20
Hi all,

Just wondered if there is a guide available for fitting an aftermarket bov. I have just bought one from importpimp (nic) and am pretty sure that I could fit it but wanted to have some kind of instructions with pictures to make sure I don't cock it up :)

Any help would be appreciated, I've done a search but not really found anything helpful and the instructions that came with it are japanese...

Theres nothing else I need to do when fitting one is there regarding setup of the engine, turbos etc? I assume its just a straight swap.... Ish :think:

Cheers all

Iv had the hks bov for about a year now, it should be very simple to fit only took me about 25 mins, the instructions are in japanese but if you take a good look at the pictures then you should be able to work out what you need to do. I am assuming you have the specific valve with fitting kit for the supra? if so everything you need is in with the kit, it goes in where the existing valve is, you wont need to do anything with the engine setup or turbos.:d

some people have these welded onto the IC intake piping i am not sure what the pros/cons of doing this are?

I can post a picture of mine fitted if it helpes.

Daston
16-06-06, 17:31
I have to put mine on the IC pipes its an NA-T

Jake
16-06-06, 17:35
If you have a UK car, an atmospheric BOV can confuse the ECU because they use a MAF airflow sensor

The j spec cars have a manifold pressure sensor and don't suffer from this problem.

Worth noting that the VVTi Supras also have a MAF, unlike the other J-specs.

MarkTheBoy
17-06-06, 11:18
Iv had the hks bov for about a year now, it should be very simple to fit only took me about 25 mins, the instructions are in japanese but if you take a good look at the pictures then you should be able to work out what you need to do. I am assuming you have the specific valve with fitting kit for the supra? if so everything you need is in with the kit, it goes in where the existing valve is, you wont need to do anything with the engine setup or turbos.:d

some people have these welded onto the IC intake piping i am not sure what the pros/cons of doing this are?

I can post a picture of mine fitted if it helpes.

If you have piccies that would be great!! Thanks

supra sam
17-06-06, 15:41
should look something like this when you are done......

http://img126.imageshack.us/img126/1415/bov0019nd.jpg

http://img233.imageshack.us/img233/7919/bov0028fo.jpg

You can spin it round so that it faces forward, it just would not quite fit under the strut brace on mine.

This is the bit you need to take out.....

http://img221.imageshack.us/img221/825/bov6aq.jpg

Hope these pics help mate :d

MarkTheBoy
17-06-06, 16:40
should look something like this when you are done......

http://img126.imageshack.us/img126/1415/bov0019nd.jpg

http://img233.imageshack.us/img233/7919/bov0028fo.jpg

You can spin it round so that it faces forward, it just would not quite fit under the strut brace on mine.

This is the bit you need to take out.....

http://img221.imageshack.us/img221/825/bov6aq.jpg

Hope these pics help mate :d

Fantastic mate, perfect pictures.
Cheers

Mark

MarkTheBoy
17-06-06, 18:57
Fitted,

Was a lot simpler than I expected, it took about half an hour, would have taken 10 mins but the bolt that goes into the "manifold" (?) that you mount the bracket to, was seized. :swear:

Looks and sounds the bee's knees. Well Pleased !!! :d

Thanks nic for supplying it and thanks to sam for the piccies and the encouragement. :salute:

supra sam
17-06-06, 19:34
well done mate enjoy, glad you got it sorted:d

Ruff_Rider
18-06-06, 15:56
Hi guys.

Bought my car a year ago with BOV already fitted. It's situated on the pipe between the intercooler and throttle body, pictured below on the right as you look. The original pipes and BOV have been removed and blankes as in second picture. I've had no problems with this but obviously it's different to yours. Is this fitted correctly? Does it affect performance or need refitting?

MarkTheBoy
18-06-06, 21:17
Hi guys.

Bought my car a year ago with BOV already fitted. It's situated on the pipe between the intercooler and throttle body, pictured below on the right as you look. The original pipes and BOV have been removed and blankes as in second picture. I've had no problems with this but obviously it's different to yours. Is this fitted correctly? Does it affect performance or need refitting?

Strange one that is mate?

Definitely fitted differently to ours but if its been running fine and dumping ok then I suppose its ok where it is, thats only a guess though.
Anyone else have any ideas?

Scoboblio
18-06-06, 22:11
That's perfectly normal AFAIK, the BOV's just been welded onto the hard pipe rather than put into the stock location.

edited: Taken from Ian's original FAQ post;

You can mount them in the same place as the stock one (kits are available to do this for most BOVs), or have a flange welded to a hard pipe somewhere (typically the one that goes into the throttle body, but anywhere between turbo and throttle body is OK).

Ruff_Rider
19-06-06, 21:16
Thanks for that, was worried for a minute. AFAIK? Explain please.

Attached detailed pic of current BOV. Can anyone tell me which make it is as there are no apparent markings on it. Thinking of switching to an HKS SSQV. May fit it to stock position if i can and replace the hard pipe with chrome bling pipe. Any views on this?

supra sam
19-06-06, 22:36
Thanks for that, was worried for a minute. AFAIK? Explain please.

Know i didn't say this but AFAIK is short for As Far As I Know.

Iv seen that Bov somewhere before? But i cant for the life of me remember who makes it:rolleyes:

MarkTheBoy
20-06-06, 15:39
Not sure what you have already but I can vouch for the HKS SSQV, its a good honest dumpvalve. Not stupidly loud but sneezes like hell when you give it lots of welly.
I have a very limited experience of bovs I admit (SSQV being my first) but have been really impressed with it.

Alex
20-06-06, 15:43
A Bov has to be mounted between the throttle body and the turbo...it doesn't really matter where between those two items it is...the SQV kit just reuses the stock point.

ben1985
31-12-06, 18:38
Are atmospheric BOVs only available to make one sound? I don't want one of those BOVs that chirps (tweets?) and am looking for one that sounds like the one on the Supra in Fast and Furious.

You know the ones that have repetitive whoosh sound (like chh chh chh chh) rather than a single whoooosh. Does that make any sense??

I was under the impression that this was a re-circulating dump valve? Am I wrong?

If not can you get aftermarket Re-circulating dump valves? And if so, anyone know of any good models?

Any advice would be very welcome!

Cheers,

Ben

uzthedentist
31-12-06, 22:09
that bov looks like a hks racing type ii im pretty certain.

theres a company called turbosmart from australia that make pipes like the one seen in the pic leading off the throttle body which you can connect a bov to, i had one on my soarer.
http://www.turbosmart.com.au/index.php?id=49

uzthedentist
31-12-06, 22:10
the one that makes the ch ch ch sound is the blitz dual drive with the little metal filter on it

dini_the_owl
01-01-07, 12:12
hi.
just a quick question,because ive heard it mentioned in various forums that BOV is a bad idea ..when the bov has let out the pressure from the system the turbos will then have to spool up again to pressurise the system therefore it is causing your turbos to work harder to keep the pressure in the system(ie. lag) and the stock one is there to protect the stock ic not to sound nice.
would anyone agree here,never had much to do with them but it does seem feesable to me?

also dosent the actuators control your turbos spooling? so when you decelarate or change gear your actuator stops the turbo accordingly,but it dosent stop dead? so why use a BOV?

Nic Uk-Ridez
02-01-07, 15:23
cause when the preasure ur creating to go one way into ur block cant go there anymore there is only one way the presure will go and thats straight back thro ur turbos cusing the fans to spinn backwards??

so instead of them sppoiling up harder they will endure a very quick change in direction every gear or lift off

which is worse than the fans spinning the same way faster n slower

if that makes sense

buster
10-02-07, 13:05
Yup Lol

edge
10-02-07, 17:10
I have a hks one on mine. It seems to make 2 noises
When using alot of throttle i get the usual whoosh noise but when just plodding about it makes chatter noise if you know wat i mean and sometimes it seems like it does a bit of both.

mk47
11-02-07, 06:50
i have a sard r2d2 on mine and it sounds amazing.. at low revs it sounds like a wastegate though, sort of a flapping noise i love it :d

SimonB
11-02-07, 15:49
i have a sard r2d2 on mine and it sounds amazing.. at low revs it sounds like a wastegate though, sort of a flapping noise i love it :d

That's because it's BOVs or compressor stall that makes that noise, not the wastegate. Wastegates don't make a noise - they only open when full boost has been reached to get rid of excess exhaust, so can only make a noise then. It's got to be one of the oldest and most annoying myths so called "wastegate chatter". There's no such thing.

amigo5
24-10-07, 19:27
one question
doesn't sema (or what ever it's name ) has been chosen the product of the year?

amigo5
24-10-07, 19:27
one question
doesn't sema BOV (or what ever it's name ) has been chosen the product of the year?

amigo5
26-10-07, 11:06
no idea >>

Brazen
03-01-08, 19:22
i Have a uk auto which came with a hks bov on. I've checked the vacum and it seems to be suckin fine but there is no sound from the dump valve at all.

Anyone have any idea's cause this one is bafflin me.

TopgunTT
07-01-08, 19:27
Has anyone on here ever had the blitz dual drive bov? think mine is stock and looking for a new sound?:search:

Brazen
30-04-08, 21:35
i Have a uk auto which came with a hks bov on. I've checked the vacum and it seems to be suckin fine but there is no sound from the dump valve at all.

Anyone have any idea's cause this one is bafflin me

Please if anyone has answers.

My mate has a blitz bov and it sounds amazing on his mr2, but from the hks one on my supra there seems to be nothing.

Has it got anything to do with it being a auto.

Ian C
02-05-08, 15:18
This is supposed to be an FAQ entry, if you have problems with your BOV please post a query up in MkIV Technical, thanks.

I'll prune this in a while, don't be offended if your post gets deleted.

-Ian

bigduderichie
05-07-08, 13:23
Hi Ian,

Although it's been on for a while - I'm new here and have just read your guide on BOV's and must say it's certainly clarified a lot for me, and am sure for many other newbies!

Thanks for a piece well written and for sharing your knowledge - long may it continue!

:d

turbo159
04-03-10, 11:02
Thanks for that, was worried for a minute. AFAIK? Explain please.

Attached detailed pic of current BOV. Can anyone tell me which make it is as there are no apparent markings on it. Thinking of switching to an HKS SSQV. May fit it to stock position if i can and replace the hard pipe with chrome bling pipe. Any views on this?


Where does the vaccum pipe connects to on this case? I have this setup ready to be fitted but dont know where the cable connect.

Can we keep the original BOV in place with this setup?