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In General => Modified Cars => Topic started by: R-A-Y on March 14, 2005, 11:01:51 PM

Title: BOV FAQ
Post by: R-A-Y on March 14, 2005, 11:01:51 PM
Hope this can help a bit for those looking at BOVs as an aftermarket mod for their car :) Anyone more knowledgeable, please feel free to correct my statements :)

Blow Off Valve FAQ

Term usage: "Blow off valves" go by several names, among them are compressor bypass valve (CBV), air by-pass valve, bypass valve (BPV), blow off valve (BOV), Diverter valve, and possibly a few others. BOV is the common and incorrect term that lumps true blow off valves and bypass valves under the same term. For the sake of correctness, this post will refer to either aftermarket BOV, aftermarket BPV or OEM BPV as these are the most correct terms.

What is the function of a blow off valve (BOV)? To release pressure from the intake tract of a turbo car when the throttle closes. It is a vacuum-actuated valve designed to releases the air to the atmosphere.

What is the function of a bypass valve (BPV)? To release pressure from the intake tract of a turbo car when the throttle closes. It is a vacuum-actuated valve designed to recirculate the air back into the intake before the turbo inlet, but after the airflow sensor.

What is the purpose of a BOV/BPV? When the throttle closes and the intake system is under pressure, the high-pressure air entering the motor will bump into the closed throttle plate, and in the absence of a BOV/BPV, a pressure wave will travel back to the turbocharger. The result is that the compressor wheel will stall (a phenomenon known as "compressor surge") and slow down very quickly. This is hard on the bearings and decreases the turbo's lifespan, but it also means the turbo will take longer to spin up the next time the throttle is opened.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" aftermarket Bovs. Obviously, there may have been bad ones sold, but not enough to report as "bad" overall.

What are the different types of aftermarket BOVs/BPVs? Different manufacturers use different methods. There are three basic types:
1. Aftermarket BPV: Similar in function to the OEM BPV where 100% of the air is recirculated.
2. Atmospheric BOV: 100% of the air is vented to the atmosphere.
3. Hybrid BOV: These depend on the manufacturer and end user settings. These can either be adjustable or manufacturer set for different percentages of atmospheric/recirculation dumping. They can also be set to work as recirculation during lower boost conditions and 100% atmospheric during higher boost conditions.

Are there any downsides to aftermarket BOVs? There have not been significant amounts of problems with BOVs. Aftermarket BOVs can and do require some light end user maintenance to keep them performing perfectly. For aftermarket hybrid BOVs that have end user defined settings, there will be an initial period of adjustment to obtain the desired recirculation/atmospheric ratio as well.

Are there any negative effects with aftermarket BOVs? Yes. The downside of releasing the air to atmosphere is that it has already been metered by the mass air sensor, and when it blows off, the ECU will be injecting the wrong amount of fuel into the cylinders. The engine temporarily runs extremely rich, meaning too much fuel is injected into the cylinders.

This temporary rich condition isn't usually that harmful, but it can cause bucking or hesitation on lift-throttle. If the condition is really bad, it can eventually foul spark plugs and even clog the catalytic converter as unburned fuel on the catalytic converter burns very hot, and too much of it can melt the cat.
Title: Re:BOV FAQ
Post by: speedyfix on March 15, 2005, 10:47:42 AM
let's sticky this for a couple of weeks ;D
Title: Re:BOV FAQ
Post by: tessaj on March 16, 2005, 08:36:39 PM
very informative and timely. salamat  8)
Title: Re:BOV FAQ
Post by: nugundam93 on April 02, 2005, 10:21:45 AM
nice article ray!  is it okay if i also post some of the BOV FAQ from wrxfanatics.com?  
Title: Re:BOV FAQ
Post by: R-A-Y on April 03, 2005, 10:14:29 PM
Quote from: nugundam93 on April 02, 2005, 10:21:45 AM
nice article ray!  is it okay if i also post some of the BOV FAQ from wrxfanatics.com?  

Of course :D ! Now one said that I am the only voice here ;D
Title: Re:BOV FAQ
Post by: nugundam93 on April 04, 2005, 06:31:04 AM
hmmm, i checked your post ray, almost same na rin pala.  anyway, if you guys wanna read, it's at http://www.wrxfanatics.com/index.php?showtopic=14107

the site also needs registration, btw.   ;D
Title: Re:BOV FAQ
Post by: R-A-Y on April 04, 2005, 07:43:15 AM
Quote from: nugundam93 on April 04, 2005, 06:31:04 AM
hmmm, i checked your post ray, almost same na rin pala.  anyway, if you guys wanna read, it's at http://www.wrxfanatics.com/index.php?showtopic=14107

the site also needs registration, btw.   ;D

Probably it came from NASIOC just like mine ;D
Title: Re:BOV FAQ
Post by: nugundam93 on April 09, 2005, 11:39:52 AM
heheheh.  anyway, all is good :D
Title: Re:BOV FAQ
Post by: Dondie on April 19, 2005, 12:45:46 PM
I have limited experience boosting cars but I would like to add briefly..

Blow-off valves are like "condoms" ;D, meaning there is always a choice between having one installed or not.

IMO, during long-term use, BOV can save your car or the turbo system itself from damage.

BOVs will enable excess pressure to release unto the atmosphere, minimizing turbo backspin. Turbo Backspin will cause the impeller on the turbine shaft to abruptly stop or stall, primarily bacause the boost pressure needs to release.

HTH :)
Title: Re:BOV FAQ
Post by: nugundam93 on April 20, 2005, 11:06:13 AM
thanks dondie!

now if i could only find a way for the 4m40 to be quieter so that the planned bov would make itself heard better.  hahahaha...
Title: re:BOV faq
Post by: badboysupra on August 18, 2005, 02:54:39 PM
well, as for the BOV's for most turbocharged cars there are the ups and downs. for engines that is running with a MAP sensor, a BOV would be OK to use compared to a AFM equiped engine. since that the AFM is before the throttle body, there would be some slight effect on the engines idle and or performance since that the metered air is sipping through the BOV (some Greddy type S & Blitz BOV's suffer from leakage) and its causing the ECU to read inaccurate readings. therefore affecting its performance. in the other hand, A MAP sensor equiped engine can still maintain & give accurate air readings to the ECU since that the MAP sensor sits behind the throtlle body (ex. all D,B,H series Honda engines and other MAP equiped JDM engines from Toyota, etc.) so that the BOV can do its job without affecting anything to the ECU. anywayz, BOV are cool, specially if your boosting. but where I live though, BOV's needs to be in the hush hush, since some cops & law enforcers out here in most Califorina city's are really strict now on modified cars. it sucks, but its all good. its part of the game. anywayz, keep it kool out there in the streets of Manila and anywhere else aite, laterz! -KBR
Title: Re:BOV FAQ
Post by: badboysupra on August 18, 2005, 03:04:37 PM
oh yeh, also I would like to recommend ya'll using HKS SSQV and Turbo XS RFL BOV. both BOV's are good between 5-25 psi (as tested on some of our cars: 1991 240SX w/ SR20DET-s14 black top, 1991 MR2 w/ 3SGTE, 1995 Supra w/ 2JZGTE.) both BOV's gives good results and sounds. aite, cheers! -KBR
Title: Re:BOV FAQ
Post by: R-A-Y on August 18, 2005, 03:15:38 PM
Yeah I heard all about those noise rules. You guys can't even run an HKS exhaust wihtout getting pulled over at least twice in a block ;D You guys should just move here ;D
Title: Re:BOV FAQ
Post by: badboysupra on August 18, 2005, 04:04:04 PM
yeh man, I wish I could move back. but anywayz, you cant really use a non CARB (California Air Resource Board) exhaust system or any high performance parts without a CARB approved sticker, or else you will get a citation if you get caught up and pulled over. but still alot of people out here are still doing it the ILLEGAL way and thats OK. as long as you dont get caught up. anywayz, I use a BORLA XR-1 3.5" race muffler w/ 3" straight through exhaust piping & 3" high flow CAT on my Supra. its pretty loud, loud enough that you can hear me rolling even though I'm like 2-3 blocks away. but I'm lucky so far that I dont get a ticket yet. anywayz, I know out there in the Philippines you get to do whatever you want in terms of modifying cars and ya'll still can get away from the cops! haha! aite, cheers! -KBR
Title: Re:BOV FAQ
Post by: turb on August 25, 2005, 04:20:53 PM
AFM engines can use recirculating BOV's so as not to affect the metered air.
Title: Re:BOV FAQ
Post by: Pro2type on October 30, 2005, 05:46:58 PM
Is it advisable to put BOV in a stock evo or sti?
Title: Re:BOV FAQ
Post by: R-A-Y on November 01, 2005, 12:25:24 AM
Very controversial mod actually for stock Evos and STis. Usually the stock recirculating BOV is sufficient for up to 400HP and no tuning.

Replacing just the BOV will make the car run overly rich for a short period on that time when you close the throttle. It seems to be not so harmless until your cat converter starts to heat up. There are even some reports that it can get som bad that it starts to glow.

If you are out for the sounds while not compromising your A/F mix, you can get any Vent to Atmosphere (VTA) BOV and just have it re-tuned, or get the hybrid BOV that is both recirculating and VTA. I believe it's Turbosmart or TurbXS that produces these hybrid BOVs

HTH :)
Title: Re:BOV FAQ
Post by: Conan® on November 01, 2005, 06:29:52 AM
Quote from: R-A-Y on November 01, 2005, 12:25:24 AM
Very controversial mod actually for stock Evos and STis. Usually the stock recirculating BOV is sufficient for up to 400HP and no tuning.

Replacing just the BOV will make the car run overly rich for a short period on that time when you close the throttle. It seems to be not so harmless until your cat converter starts to heat up. There are even some reports that it can get som bad that it starts to glow.

If you are out for the sounds while not compromising your A/F mix, you can get any Vent to Atmosphere (VTA) BOV and just have it re-tuned, or get the hybrid BOV that is both recirculating and VTA. I believe it's Turbosmart or TurbXS that produces these hybrid BOVs

HTH :)

OT, It's time to remove your catalytic converter for more power gains! ;D I added about 30 kph to my top end when I removed mine.
Title: Re:BOV FAQ
Post by: R-A-Y on November 01, 2005, 10:28:05 AM
Quote from: Conan on November 01, 2005, 06:29:52 AM
OT, It's time to remove your catalytic converter for more power gains! ;D I added about 30 kph to my top end when I removed mine.

Hahahaha yes I have to remove it ;D Very very soon :)
Title: Re:BOV FAQ
Post by: Conan® on November 05, 2005, 09:50:18 PM
With the kind help of Speedyfix I modified my factory Blow-Off Valve from this modification guide here:

http://www.nissansilvia.co.nz/tech/factorybov.htm

We blocked off the small hole with a screw and some Loctite.

This is strictly for Nissan Silvia BOV's. Though I haven't really pushed the car yet since it's been raining since I had it done, but off hand my car is a bit more responsive in the lower end and there's a slightly louder indication that the BOV is working more compared to before. It's not very loud though as it is "plumbed back" into the intake, but I can here it through my aftermarket air filter.
Title: Re:BOV FAQ
Post by: zoids on November 16, 2005, 12:08:21 AM
Quote from: Conan on November 01, 2005, 06:29:52 AM
OT, It's time to remove your catalytic converter for more power gains! ;D I added about 30 kph to my top end when I removed mine.

OT:  cooonan, you're going to do some harm on  the   environment.. >:(....remember, more carbon monoxide causes greenhouse effect.. :o....and then, the emission test when registering your vehicle... :P....peace man... ;D...
Title: Re:BOV FAQ
Post by: borly on November 16, 2005, 12:35:43 AM
i just read the article, it's amazing how blocking of that small hole can increase performance... :)

hehe angelo and migs s14 tandem... twin drift!
Title: Re:BOV FAQ
Post by: Conan® on November 16, 2005, 10:18:03 AM
Quote from: zoids on November 16, 2005, 12:08:21 AM
OT:  cooonan, you're going to do some harm on  the   environment.. >:(....remember, more carbon monoxide causes greenhouse effect.. :o....and then, the emission test when registering your vehicle... :P....peace man... ;D...

Actually bro I pass the emissions test quite easily even without the catalytic converter. ;D

@Borly si Migs manual tranny so it will be much easier to drift in his car. ;)
Title: Re:BOV FAQ
Post by: zoids on November 16, 2005, 10:01:12 PM
Quote from: Conan on November 16, 2005, 10:18:03 AM
Actually bro I pass the emissions test quite easily even without the catalytic converter. ;D


OT: ha?!... i might as well remove mine then ::) do you think it would have the same effect on mine..N/A 'matic? ???
Title: Re:BOV FAQ
Post by: R-A-Y on November 17, 2005, 01:04:45 AM
I believe it will. We have pretty low emission standards here eh.
Title: Re:BOV FAQ
Post by: zoids on November 20, 2005, 11:19:25 PM
Quote from: R-A-Y on November 17, 2005, 01:04:45 AM
I believe it will. We have pretty low emission standards here eh.

ok R-A-Y will do it sometime this week...was very busy this weekend. thank you  :D
Title: Re:BOV FAQ
Post by: borly on November 27, 2005, 10:01:20 AM
i recently heard the sard r2d2 bov of my friend... hehehe twas really nice... it sounds like a whip!
Title: Re:BOV FAQ
Post by: Conan® on November 27, 2005, 10:42:10 AM
Quote from: andrew_borly on November 27, 2005, 10:01:20 AM
i recently heard the sard r2d2 bov of my friend... hehehe twas really nice... it sounds like a whip!

On what car was it installed? Did he get it from Autoplus?
Title: Re:BOV FAQ
Post by: CSA-entrepreneur on January 23, 2006, 12:00:56 AM
with my evo, back then, i had a TBE (turbo back exhaust) as my first mod. after that, ive been hearing a little spool up.. i then installed a HKS RS Intake (the one that looks like a beehive), with stock BOV, and damn that was loud! the evo stock MR BOV actually could hold my boost (which was tuned at 20.5 PSI with my manual boost controller), but when i got my greddy type-s bov, it sounded so sweet..

i vented it to atmosphere and whoa, i love revving up at inside parking lot structures by the wall at corners with the hood popped.
Title: Re:BOV FAQ
Post by: NSR on September 18, 2006, 02:12:48 AM
Quote from: CSA-entrepreneur on January 23, 2006, 12:00:56 AM
i vented it to atmosphere and whoa, i love revving up at inside parking lot structures by the wall at corners with the hood popped.

oohh..how i envy the feeling of simply revving up then hearing your BOV scream  :-\
Title: Re: BOV FAQ
Post by: lantraluvr on September 09, 2007, 04:59:27 PM
Does anyone have information if turbodiesels can be fitted with BOVs?
Title: Re: BOV FAQ
Post by: NSR on March 12, 2008, 11:59:56 PM
Just a question re. BOV spring tensions, what are the consequences of tightening/loosening them? ???
Title: Re: BOV FAQ
Post by: jela on October 09, 2008, 11:11:17 PM
i have a dilemma in choosing which BOV to use and which is better, HKS SSQV 2 or Greddy type RS ???
Title: Re: BOV FAQ
Post by: autofreak03 on October 15, 2008, 08:32:27 PM
go for the hks ssqv or blitz supersound
Title: Re: BOV FAQ
Post by: Cris_andre on January 12, 2009, 10:36:19 PM
nice find paps!
Title: Re: BOV FAQ
Post by: giant killer on February 26, 2009, 10:44:13 AM
Quote from: lantraluvr on September 09, 2007, 04:59:27 PM
Does anyone have information if turbodiesels can be fitted with BOVs?

kung ang diesel engine ay may throttle body (efi) you can use any BOV...pero kung walang t.body or kung old skul diesel engine edi pressure regulator lang ang ikabit para tumaas ang boost...

Title: Re: BOV FAQ
Post by: dud069 on January 03, 2014, 01:01:10 PM
I think Speedlab has BOV's for Turbo diesels
Title: Re: BOV FAQ
Post by: Chino De Dios on June 30, 2016, 12:24:05 AM
Awesome thread! I have a question though. I am using a 4G93T engine, and I am having some issues on the idling. It also shuts off the engine when I don't step on the accelerator especially at cold start. One friend told me to get my BOV to recirculating setup. I am using a Blitz SS BOV.

Thanks in advance for the suggestions!