07 September
Blow-off valve functioning and installation
Today in the Atomic Labs we’ll be going through the installation of an atmospheric blow-off valve (BOV). So what, exactly, is this valve thingy and what does it do?
On a turbocharged engine, when the turbo spools up it pressurises the intake system – from the compressor, past the throttle body and through the inlet manifold, forcing more air into the combustion chambers. This is how a turbo produces more power, but I’ll go into the specifics in a later article.
When you take your foot off the accelerator pedal, the throttle body closes – the stream of pressurised air created by the turbocharger is now cut off from the inlet manifold. The only way it can escape is back up the intake stream, surging into the turbo compressor. This reversal of intake charge pulse can put additional strain on the turbo components, as well as reducing the compressor wheel’s rotational velocity. This means that the turbo will take longer to spool up when the throttle is opened again.
A valve placed before the throttle body cures this problem by allowing the pressurised charge to escape the intake system, keeping the compressor spinning and reducing turbo lag. I won’t go into the specific details of how the valve opens when needed, but if you want to know more then email me. Many turbocharged cars come with such a valve from the factory, but they are recirculator valves rather than BOVs – the compressed air that escapes is plumbed back into the intake before the turbo. BOVs vent this air to the atmosphere instead.
So why install an aftermarket BOV? They provide improved throttle response and can hold much higher boost levels compared to the factory-fitted version, and as a bonus because they vent to the atmosphere they provide that sought-after “psssht” sound when shifting gear or free-revving. Plus they look damn cool, if that’s your thing.
The only drawback to this type of valve occurs on cars with air flow meters. Because the engine is venting air that has already been measured by the MAF, the car’s computer adds a little too much fuel for the air that is left, resulting in a rich mixture for a short period of time. This can sometimes result in backfiring, but results vary from one car to the next. This can usually be addressed by proper tuning. Again, I won’t go into details, cos it’s not necessary at this point.
In most cases, a BOV is fitted to the car’s factory boost hoses, or is attached to a weld-on adaptor plate for upgraded intercooler systems. The choice depends on your car’s level of tune, and what your needs are.
Okay, onto the installation. The BOV in question is a Stealth FX, made by Go Fast Bits in Australia. This is a top of the line model, made from billet aluminium, and is built like a tank. I chose one with a mounting flange specifically for the Nissan S14 200SX, eliminating the need to adapt anything for fitment. While this can save a bit of hassle, a generic-fit BOV is nonetheless fairly easy to install.
[Disclaimer: we accept no responsibility for you breaking your BOV, your car, or yourself, scaring your cat, spilling your beer, or any damage incurred by following this procedure. If you are in any doubt whatsoever, please have your installation carried out by a professional.]
First off, the battery is removed, allowing easy access to the existing factory recirculating valve. (This will vary from car to car). Here you can see it in place. The large lower hose is connected to the boost piping, and the upper one is joined to the intake system just after the airflow meter. The small hose at the top of the valve is a vacuum line, which is connected to the intake after the throttle body. This provides pressure differential required for the valve to actuate.
(Please excuse the crusty battery tray, it’s the only part that doesn’t get cleaned regularly 
)
The factory valve has been removed in the next picture. Hose clamps were loosened and simply slipped off, but I recommend that you use a screwdriver to push the vacuum line off – it’s on very tight, and simply tugging on it might cause damage. Much squirming and cursing was involved – the space is tight, and some of the screws are damn tricky to reach. You can see the mounting points to the left of the hose.
This is the new BOV attached to the factory flange, a direct snug fit with minimum hassle thanks to the vehicle-specific mount. The silver trumpet thingy is the valve’s atmospheric outlet, and the silver cap can be twisted to adjust the internal spring setting.
Here we have two different outlet trumpets. On the left is the regular one, on the right is a variant that alters the noise produced by the valve when venting. I decided to go with the longer one after comparing the sounds.
A couple of screws and hose clamps later, the new BOV is in place. It’s a tight squeeze to get it under the fuse box, but once in place it sits perfectly.
Once installed, some minor adjustments have to be made to the valve spring. This affects how quickly the valve actuates and how long it stays open for. If left open too long, the engine will stumble, but if if it shuts too quickly not all of the pressurised intake charge will escape. A couple of short drives with some adjustment in between is enough to get things sorted.
Total time to install: 20 minutes and one beer. This will take a bit longer if you are using a generic-fit BOV, but nothing hectic. A six-pack at the most. Overall, this is an effective, rewarding, yet easy to accomplish modification. BOVs range from a few hundred rand for a no-name-brand hunk o’ junk, to a few thousand for big-name high-performance models, with many in between. As always, you get what you pay for – don’t spend too much if you don’t need it, but neither should you skimp on quality. Find the compromise that suits you and your car.
A quick note: if you drive an stock, unmodified turbo car, the benefits from fitting an aftermarket BOV are small, and on factory boost settings you can expect a small amount of engine bog between gears. However, if you’re seeking vroooooompssshhhtness, it’s the price you pay.
Before anyone asks: *no*, there is no point in fitting a BOV to a car without a turbocharger . And yes, I have been asked this before.
A word of advice to anyone planning on getting hands-on with their car: buy some latex gloves, the kind doctors and dentists use. They’re dirt cheap, and save you the hassle of cleaning your hands – just toss em away when you’re done. They also provide the added bonus of preventing minor scrapes and cuts. Unless you’re uber-careful / experienced, you *will* bleed a little every time you get under the hood.
Until next time, may your boost be high and your beer be cold =).
Questions? Comments? Requests? tachyon (at) carblog (dot) co (dot) za.
(C) 2006
December 7th, 2006 at 4:55 pm
Hi Guys anybody who can referr ne to a good place in cape town for an exhaust manifold?
December 7th, 2006 at 4:56 pm
Hi guys – anybody who can referr me to a good company for an exhaust manifild / branch in cape town for my Nissan 200sx -S14
Thnxs
Ray
April 26th, 2007 at 3:48 pm
I have a turbo diesel ute and want to put a BOV on it. It is not efi so I’ guessing I don’t need to worry about the air flow metre.
July 9th, 2007 at 8:55 am
Hi Can some one tell me, does blowoff vave can be installed without turbo or intake system?
July 9th, 2007 at 8:56 am
Sorry for the typo….. Hi Can some one tell me, does blow off valve can be installed without turbo or intake system? if yes how to install? Thanks in Advance!!!
August 2nd, 2007 at 7:40 pm
Hey Can I install a Blow off Valve through my cold air intake?
September 30th, 2007 at 11:29 pm
on what part do u install the BOV? Where or on top of what do u install it? Thanks
October 17th, 2007 at 8:59 am
sorry but is that possible to fit a BOV on a engine without turbo just filter intake to hear the sound ? thanks .
October 28th, 2007 at 3:41 am
im getting ready to run twin turbos witch will be set up for carb, i have one blow off valve where can i put one of these. do i drill a hole in the hat, these are t3s turbos with built in waste gates this in on chevy V8, got it from turbonetics. will it work by putting both pipes together right before the hat and having one of these in the center. greg.
November 27th, 2007 at 9:50 am
The BOV will, sorry to say, not work on a naturally aspirated car. i.e Non turbo.
November 30th, 2007 at 9:23 am
hey can u have a BOV without a turbo or intake system?
November 30th, 2007 at 11:30 pm
im planing in installing a turbo into my dsm 420a 2.0 non turbo engine and i don not know how to hook up the line of the BOV (the plastic hose)
December 18th, 2007 at 12:53 am
A BOV requires that the pressure in your intake is higher than that outside – therefore, unless you have some form of forced induction (turbo- or supercharger) to create that pressure, there is no point in installing one. You could if you reeeally wanted to, but it wouldn’t do anything
January 3rd, 2008 at 1:51 am
Is it true the blowoff valve won’t work without a supercharger/turbo and someone please explain why.
January 20th, 2008 at 5:59 am
Is it possible to change the amount of pressure that a BOV needs to “go off”?
January 21st, 2008 at 1:24 pm
Mr nobody: Most quality BOVs include a spring adjustment mechanism of some kind. But unless you’re running extremely low boost (less than 0.1 bar), this is used primarly to alter how long the valve stays open for.
iskeetvanilla: Yep, you need a turbo or supercharger for a BOV to work. See my previous post just above yours.
March 19th, 2008 at 6:04 am
Hey i have a 88 chrysler conquest that boosts about 9 pounds with the stock turbo and i was wondering if i can get more boost out of it without going with a bigger turbo
March 19th, 2008 at 1:30 pm
Nathan: depending on the size of the stock turbo, you should be able to increase the boost a little without much trouble. You’ll need a manual boost controller, which can be found for under $100. Perrin make a very nice one for around $90.
You also have to make sure that enough fuel is being provided for the increased boost level. For this, you’ll need aftermarket management of some kind – a basic piggyback system will do fine. If you *don’t* add more fuel, the engine will lean out and result in detonation – a very bad thing!
March 21st, 2008 at 11:05 pm
My car has 3 vacuum lines going to the waste gate which line would i have to hook the boost controller to. My car doesnt have a blow off valve either. so im not to sure where to put it
March 22nd, 2008 at 7:52 am
hey guys umm i was just wondering if we could actually install a blow off valve with out a turbo
if you can could you please tell me how to install
March 23rd, 2008 at 11:24 am
Hi all
if this supercharger installed in my car, can the BOV work perfectly? please see link below for the super charger image. please help
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=330221262428&ssPageName=ADME:X:RTQ:MOTORS:1123#ebayphotohosting
March 24th, 2008 at 11:50 pm
Nathan: rather have your boost controller installed by a professional. If you connect anything incorrectly, you could destroy your engine and/or turbocharger. Have the BOV put in at the same time.
luke: as stated numerous time above, no turbo means no BOV.
Benjie: I hate to break it to you, but that electric supercharger is completely ineffective – so there is no point installing a BOV.
March 25th, 2008 at 7:57 am
So the electric supercharger is useless? it will not increase my HP at all?
March 25th, 2008 at 1:05 pm
Benjie: unfortunately not
. I have spoken to several people who have installed these low-price kits, and none of them have achieved any tangible benefits.
There *are* effective electric supercharger solutions, but they require additional batteries that are recharged from a mains supply and not the car battery. They generally cost hundreds of dollars.
Google the term “electric supercharger”, and you’ll find some articles on why the budget kits don’t work, as well as info on the expensive ones that do work.
March 27th, 2008 at 8:16 am
I have a ZX14 (kawasaki) with a Stage 1 turbo kit. I run up to 7-8 PSI of boost with a T3/T4 Hybred. I just installed an RS type BOV that I purchased off of Ebay new Greddy style but not sure who makes it maybe JDM. I’m using the same vacuum lines that go to the MAP sensor. My problem is that the BOV isn’t working. At idle I’m at -10 PSI and up to 20 on decel on the Vacuum/Boost gage but the BOV doesn’t open when coming off throttle above 4PSI of boost, instead it still surges through the compressor. The BOV holds vacuum fine and seems to be intact. Any ideas as to why this isn’t working? TRhe piston moves slightly when accelerating instead of decelerating yet the MAP sensor hoses come off the TBs below the throttle plates. Is it possible the spring rate is too high to let it open?
Any advice is appreciated.
TJ
April 8th, 2008 at 12:50 am
can..I.install.a.bov..on.my.stock..supercharger..
April 26th, 2008 at 4:59 am
hi.. i have turbo diesel. i want to put the BOV HKS on to my enjine.. i have problem with the vacum tube.. where can i put it?..
May 15th, 2008 at 10:26 pm
i buy a utr bov from malaisa. they said that i will work on non turbo car but i can`t find any place to set it .plz help me
July 10th, 2008 at 2:17 am
what kind of BOV can i put in my jetta gli
August 19th, 2008 at 7:40 am
Great article, thanks for the good info and pics.
September 26th, 2008 at 12:03 pm
hey ive got a Celica GT-FOUR 1990.. had it for a while an just got a brand new GFB Mak1 blow off valve.. sounds good, an helps the turbo keep spoling betwen shifts an has got even beter respose now.. but since the b.o.v, the turbo doesnt seem to be spoling as much from 80-140+ any one no y that is.. some thing to do with the air flow meter fu*king the map reading?
October 14th, 2008 at 6:31 pm
Can anybody tell me if i can have a turbo installed on my ford bantam 1,3i, an if so a place in Cape Town
November 3rd, 2008 at 3:22 am
hi i have a non-turbo 4wd and i’ve heard that i can put a blow off valve on it but im not to sure how to install it. any ideas? i kno that it wont give it anymore power i just want the sound to top off the exhusts note
November 3rd, 2008 at 7:26 pm
Hi i have a 2.5 diesel Isuzu non turbo what mods do i have 2 make to put a turbo on it?I have a 2.8 turbo diesel Isuzu motor that has a hole in the blok can i put the turbo on the 2.5 or do i have 2 split the motor and replace parts in the motor before i put the turbo on the 2.5 motor?
November 4th, 2008 at 4:26 pm
are people reali that stupid u cnt put a bov in an engine wifout a turbo or supercharger becoz theres no bak pressure 2 vent if u rev heads want the noise then get a turbo and let tha ppl with gud questions ask
I want to find out if its possible to install a bov in a turbo diesel
December 21st, 2008 at 6:52 pm
hey ppl… i want to fit A BOV on my isuzu kb 280 turbo diesel.. i’ve got the aftermarket BOV..How would i go about installing it myself???
February 19th, 2009 at 1:02 am
jay & King …
Yes you can put a BOV on a turbo diesel. You won’t derive an awful lot of benefit, because diesel turbos are usually smaller than the petrol equivalent and thus spin up fast anyway, but you’ll still get the awesome sound.
They would be fitted in exactly the same way, following the same principles, but you would probably have to weld a mounting flange onto the boost piping.
February 22nd, 2009 at 12:32 pm
hi i have cielo daewoo car, there is no turbo,but i want put bovalve on it,IS IT POSIBAL ,pls help me
March 6th, 2009 at 7:09 pm
i have a toyota diesel engine with turbo, and makes 25 psi boost. can i will fit a bov valve??? does the boost go less when i fitted??? hellppp
Thanks in Advance
March 7th, 2009 at 2:08 am
Mr Fade –
Yup, you can fit a BOV no problem, and your boost will not decrease. Depending on your setup, you may very well see better boost response. However, diesel turbos are less suscepible to boost lag than petrol equivalents, so your results may be less noticeable accordingly.
March 7th, 2009 at 6:05 pm
10z king,1 more mr atomic can u tell me same tips with a little bit of money to make my engine more accelerating
March 7th, 2009 at 7:18 pm
The cheapest way to get your car to accelerate faster is to lighten it – take out your back seats, remove spare tyre and door panels, etc. Zero cost, extra acceleration
March 8th, 2009 at 2:08 pm
ok 10q king,i have a MANUAL boost controller and i going u install it. i have a idea how to install it but i m not sure.Can you tell me the way how to install it plss??? it will help the turbo u work well??
Thanks in Advance
March 10th, 2009 at 6:34 am
1.Is these pictures non turbo, or it is turbo’d.
2.If i have a Great intake system, and an electric Supercharger[Rice I kno]
Would i get the sound? I dont care the purpose of the BOV, i just love the sound. I know its a Rice question.
3.Can I install it on the Electric Supercharger?
4.If so where?
5.If not , where can i install a bov and get the sound?
March 13th, 2009 at 3:45 pm
Hi Mike
1) Read the article and see
2) Do yourself a favour and don’t buy an electric supercharger. The vast majority of the DIY ones for sale are scams and lies. There are one or two bona-fide units out there, and they cost the same as a turbo set up. Save your money!
3) If you do buy a proper electric supercharger (not one of the useless sub-$500 ones), yes you could.
4) It’s probably best if you leave that to the guys who install the supercharger.
5) As stated previously, without forced induction, no BOV sound…
March 16th, 2009 at 12:33 am
I have a 97 maxima with a cold air intake with no turbo. Can i install a BOV?
March 17th, 2009 at 9:25 am
Hi i have a 89 toyota mr2 supercharged and i was wondering if i can install a bov. If i can please tell me how i can set it up thank you.
March 28th, 2009 at 7:13 pm
Can a bov be installed on an automatic car that has a cold air intake and no turbo?
April 6th, 2009 at 9:56 pm
you guys are all dumb, read post before you ask questions.
if you car has NO turbo then No you cannot have a BOV
go ahead and buy a fake exaust unit that sounds like a turbo…google search “fake BOV” and thats your answer.
and for others, you can turbo any combustion engine but that doesnt mean it is easy…so make it easy and pick yourself up a factory turbocharged car for cheap.
April 24th, 2009 at 4:03 am
Hey guys i have question. Can i Install a blow off valve through my intake? if yes please email me at dhendricks20@yahoo.com. Thanks guys
May 3rd, 2009 at 7:10 pm
hey
Maybe you could tell me if the bov could be installed on td engine ,you know without intercooler only turbo diesel ,and would it make that awesome sound ?
May 4th, 2009 at 10:06 am
Duonis: yup, you can install one no problem. The blow-off sound won’t be quite as loud as on a typical turbo petrol engine, but you will get it
June 6th, 2009 at 6:56 pm
To those that keep asking if they can fit a BOV to a non turbo car, I have a really cool idea that works. When you drive your car and want the wooosh sound, Shake up a bottle of Coke and take the lid off. You can vary the sound to you depending on how quick or slow the cap comes off
FFS, READ other peoples comments!! NO POINT PUTTING A BOV ONTO A CAR THAT DOESNT HAVE FORCED INDUCTION! The BOV works under pressure hense the pretty little woosh / flu (sneeze) / bird noises, It is releasing the excess pressure built up during good gear changes. Unless you want it there for people to admire, save your pennies and put a photo of one in your engine bay. It does the same thing without having forced induction.
As for the cheaper electric supercharges etc, I wouldn’t even consider putting one on my 2 stroke brush cutter! Seriously, spend the money if you want something reliable. Don’t waste your hard earned cash on cheap junk. You will only pay more later to have it done properly when the cheap stuff fails.
Oh and a nice write up done for the publisher.
June 9th, 2009 at 1:05 pm
Hehehe! Well said, Paul
June 30th, 2009 at 4:19 am
i got an aftermarket BOV, it releases into the atmosphere. but it also has an extra fitting, does this go to a vaccume joint on the inlet?
August 14th, 2009 at 12:30 am
can i install a blow off valve on my 2000 jeep cherokee with out turbo and intake? If so where do i install it?
August 16th, 2009 at 11:12 pm
I’ve read many negative posts regarding a BOV on a Golf MK5 GTI, which I own. Many like it, many don’t. Those that don’t have good reasons, those which for the life of me I cannot remember at present! Some also do not want the loud air release sound and want a quiet ride, while some do (and also fit cone air filters!). I do recommend that people do additional research and not just think it’s all rosy, from what I remember there are drawbacks too. If you are going to buy a blow-off valve (and / or a diverter valve) a good company I’d recommend is Forge in the UK. Top quality.
September 2nd, 2009 at 12:09 pm
Can I put a blow off valve in my 2003 Kia Rio LS car with a standard 1.5L engine
September 3rd, 2009 at 10:25 pm
mike & Derek: no turbo = no BOV
Andrew: good points there
. The GTI has a factory-fitted recirculating BOV, which works very well. The only reason to fit an aftermarket unit is for the release noise or if you heavily modify the motor and need a tougher valve.
September 12th, 2009 at 9:10 am
Mr Atomic,
I’ve been reading on all these posts about all these guys asking you about the BOVs so I’m just going to put my question strait towards you if I may. I have a 2006 Toyota Corolla 5 speed manual, i just ordered a cold air intake. I am looking into getting a turbo and BOV for it. i was wondering if i had to get a new exhaust system in order to put that much work into the engine. I was also wondering if you think its even worth paying money to upgrade a 1.8 liter engine. I’d love to chat with you about what to look into for the car if you could. thanks a bunch
September 13th, 2009 at 4:41 pm
I just got a 2010 Hyundai Genesis 2.0T and I’ve been wanting to put a BOV on it. Any suggestions? and I need the website and if possible is it possible to do it yourself. (Since its pretty new out there, there really isnt much help on things to find for it or how to do it.)
Mr. Atomic: You seem to know your car stuff. Any Suggestions?
September 14th, 2009 at 11:23 am
Barry: You can upgrade any engine and get good results
. I know at least 2 people who have turbocharged Diahatsu. And your 1800 Toyota is a pretty popular engine to modify – if you have the budget to do it properly, I’d say go for it. An alternative to consider is putting in a 4AGZE motor, and ditching the supercharger in favour of a turbo. That way you’ll already have the necessary forged pistons, bigger injectors and exhaust manifold. Either way, you will have to replace your exhaust for optimum results, but only once the turbo conversion is done. Feel free to email me if you need more info.
September 14th, 2009 at 11:27 am
Leo: It is a very new car, so there aren’t any bolt-on BOVs for it yet. You could wait for one of the manufacturers to release a kit, or you could get a universal-fit unit (eg. the HKS SQV 3). If you go with the latter option, it’s probably not something you can do yourself (unless you’re handy with a welding kit). Any good performance shop will be able to do the necessary fitment for a nominal charge though
September 21st, 2009 at 2:28 pm
Hey guys i dont really know much the whole car thing yet, im buying a stock Nissan 300ZX with a V6 VG40DE engine, it therefore has no turbocharger, i was wondering if i could have any info as to whether one would fit? if so what is compatibile whats not? and also arough price or link to a site which could show me thanks
September 21st, 2009 at 2:29 pm
sorry VG30DE on that last engine
my bad
September 26th, 2009 at 2:48 am
Mr. Atomic,
thanks for the help if you could e-mail me at barrybezzy@yahoo.com itd help alot, thanks in advance
October 3rd, 2009 at 2:07 am
hey i just bought an 02 jetta gls 1.8T and i have heard they put out a lot of power but i was wondering if i could put a BOV on my stock turbo……and if anyone knows of a good VW mechanic near Columbus,OH then enlighten me plz for future reference…….thanks
October 28th, 2009 at 12:35 pm
Tobi: your best bet is to get your hands on a VG30DETT, the twin turbo model of the same engine. This will have the necessary internals already, and will save you from the many headaches of turbocharging your existing engine. It will work out cheaper too
Nick: yup, you can install a BOV no problem. If you locate one made specifically for your model of car you could probably do it yourself in under an hour. The turbo on your car is fairly small, so stick with a small BOV or your engine response may suffer. Just be aware that this will void any warranty you may have
November 3rd, 2009 at 2:06 pm
I have a 2002 wrx and i had recently bought i aftermarket bov and was wondering if you have any tips to get the max performance out of it also it does run rich becasue when i shift in to nuetral when in motion the rpms go almost to 200 any tips?
January 26th, 2010 at 3:45 am
yes.. there is a way, You’ll need to custom make a new exhaust… what you do is, You get a U-bend, and attatch it to the end of your header(under your car)… then route the exhaust back towards the motor, Straight into your throttlebody…This will create the needed pressure for sound.. add a BOV (buy one for $20 from a salvage yard) hook up the vac line, and enjoy!
February 4th, 2010 at 3:25 pm
why would you want a dump valve on a non turbo car ? fools .
February 23rd, 2010 at 12:12 pm
yes u can run a bov on a non turbo car just run it off the oil preassure line and block the turbo discharge pipe on the bov
February 27th, 2010 at 10:35 pm
I have a: 1995 Mitsubishi Eclipse GS-T Stock Turbo 4g63 4cyl 2.0L
Stock CBV (AKA) BOV, is making irregular noises when it gets to the next shift, almost like a whistling sound, Could there be possible leaks int he stock blow off vsalve? Also, The car stumbles at times when shifting, would this aftermarket BOV & Air intake fix those issues?
http://www.extremestyling.com/GReddy-Type-RS-Blow-Off-Valve/M/B001GNHBL6.htm
http://www.andysautosport.com/mitsubishi/1995_1999_eclipse/performance/intakes/short_ram_intakes/injen/inje00128739.html
March 8th, 2010 at 6:57 pm
Brandon:
It is possible that the BOV is simply becoming worn – the whistling sound is either from the outlet valve taking longer to close, creating a small aperture of minor duration, or a leak elsewhere in the valve as you suspect. Either problem may cause your air flow sensor to misallocate fuel delivery which causes the stumble.
An aftermarket BOV will help, just be sure it is installed and set up properly to keep fuelling accurate. If you’re running stock settings you don’t need to spend huge $$$, but if you have increased the boost a higher-quality model is a better idea.