BOV OR NO BOV??

[JBAE]

heard good and bad things about having one and not having one,
just wondering on what yous think about them personally im over the novelty of a bov psssshht, but ive heard taking it of can cause damage to the turbo wheel? and also heard that running with one can cause the turbo to overspeed or something?? obviuosly im not up to speed with this or i wouldnt be asking but is it safe to take the bov of completely and run nothing at all not even a plumback?
my car is a S4 FC with a hiflow(what i was told when i brought the car) if that makes any differences and plan of running an external gate later on down the track when i upgrade the turbo if thats something i need to consider also?

[deeman111]

Im running a 12AT with series 5 hi-flow turbo, no BOV and i hvent had any problems.. I know there has been a few debates on ausrotor about it before. I think people agreed to disagree.

Unless there is some real hard evidence that it can cause noticable damage i wont fork out $$$ for something to make a noise. Ratehr just keep the money for fuel

-James

[evil1]

jsut get a plumb back dude

[bodybodyrock]

no bov for me, no probs at all

[McKVNT]

Running no BOV hasn't caused any problems for me, the car is daily driven and on the track..

[yumafia]

On my 180sx sr20det before i sold it i ran it 1 day without bov, mate everythin went wrong for some reason it was popin flames out da exhaust like crazy than i put a plumb back on. No probs ever u need a bov 2 release the extra pressure but the plumb back does the job havin the loud one one juss gets cops on your back. But i heard some ppl have no probs so i dunno.

[Joe]

IMHO, you need a BOV, even a stocker or a plumb back....if your running lots of boost, it can cause issues with some turbos.

I've seen the results of a BOV done up way too tight on a WRX with an aftermarket IHI VF series snail....a few of the blades tore straight off the compressor wheel. No BOV at all would have been even worse.

[JBAE]

looking around i found this yet to read it yet but mite be usefull obviiously for myself but anyone else interested

http://ausrotary.dntinternet.com/forums/viewtopic.php?t=17113&highlight=

[Nemi]

no bov also no problems

[Drift_R32]

im not really a turbo person but how does the biult up pressure get released if theres no BOV?

[Nickevox]

i spoke to lumpy and he said if you aint running bull**** aount of boost having no bov wont harm anything, unless you got over 1bar then you will need one

[upgarage]

im not really a turbo person but how does the biult up pressure get released if theres no BOV? it doesnt

[joey89]

im not really a turbo person but how does the biult up pressure get released if theres no BOV?
Yeah it doesnt it gets pushed back through the turbo and thats when you hear that fully sick flutter sound that every VL turbo has :D

[Nemi]

i spoke to lumpy and he said if you aint running bull**** aount of boost having no bov wont harm anything, unless you got over 1bar then you will need one
I was running 1.2 bar with no problems will be running more soon.

no bov fuks with afms a lil so you can get some wild decel flames thats about all. You also don't have to deal with that fuking ricer psssst.

[Kilma]

i spoke to lumpy and he said if you aint running bull**** aount of boost having no bov wont harm anything, unless you got over 1bar then you will need one
That was my opinion as well. I didn't think it was necessary unless you were running big boost, but still helpful when running low boost. I just have a plumb back. It is quiet enough for me.

[Philthy]

i have a loud bov it is oh so very gay. u get sick of it literally after about a day. stocko bovs ftw.

[ZERO]

i have a loud bov it is oh so very gay. u get sick of it literally after about a day. stocko bovs ftw.

Same!!!

I have a sr20det, and hear if you dont run a plumb back it starts to over fuel so looking around for a good plumb back. I have a GFB BOV atm.... FTL :werd:

[s13-steve]

i hate my BOV, id rather just flutter

[Brockas]

There's a reason turbo cars come with a BOV from factory. If it wasn't neccessary then manufactures wouldn't bother.

Having said that, loud BOV's piss you off about 1 week after you get them...

[Miami]

I personally ran no BOV for a few months at 0.9 bar, with flutter, and having now fitted a basic Blitz one opened up as far as it will go, the noticeable "performance gain" is a reduced lag in coming back onto boost after gearshifts. Mine's not plumbed back, and is positioned such that it can be very loud on full boost, but daily driving it just gives a gentle "whoosh".

Thew following is pulled directly off Pole Position Motorsport forums...throw the info out there, and let people make an informed decision themselves I think is going to be the only answer in this debate.

BLOW OFF VALVES (BOV):

Blow-off valves have become more of a fashion accessory than a performance item- they have to make a certain sound or look cool. However, there's more to them than that...

Sometimes the simplest mechanical parts are the easiest to confuse, especially when they are inappropriately named- as in the case of the humble blow-off valve. This is now standard fitment to every factory turbocharged petrol engine. We see a lot of confusion in the performance scene as to the actual purpose of a blow-off valve, how it works and, more to the point, what type of performance benefit you gain from fitting one.

Naming Confusion

By definition, the name blow-off valve for this piece of automotive technology is incorrect. This component should be referred to as a 'compressor-bypass valve'. There is such a thing as a blow-off valve (over-pressure valve) and it is a device mounted (normally) after the throttle body, which is nothing more than a spring loaded poppet-style valve with a calibrated spring tension. Once the boost pressure in the manifold increases beyond the spring tension, the blow-off valve pushes open and lets the excess boost pressure escape.

Anyone that has looked under the bonnet of a Pulsar ET Turbo or even a VL Turbo will have noticed this device protruding from the manifold. It is a crude mechanical device designed to safeguard the engine and was made obsolete the moment that software gurus learnt how to write the dreaded over-boost ‘fuel cut’ into factory computers. Long live the fuel-cut defender?!

What Does It Do?

You need to refer to the diagrams displayed (below) to get a true understanding of how the BOV works. Essentially its whole purpose is to stop airflow reversing and knocking tens of thousands of rpm from the turbo when the throttle is snapped shut. Imagine a mass of air traveling at great speed being pushed through a wide open throttle butterfly for a moment. Then imagine that butterfly snapping shut and the airflow reversing back towards the turbo compressor. It’s this massive short-duration pressure build-up that causes the compressor in some cases to stall, and others to fail altogether.

With a BOV installed, the moment the engine comes onto vacuum (throttle is shut- engine remains drawing/ ‘sucking’ air behind throttle) and there is pressure in the inlet tract (between the turbo and the throttle body), the BOV will open and vent this air charge to one atmosphere. While never being able to be 100% effective, the BOV can almost completely stop the massive pressure spike in the inlet tract (also known technically as “cavitation”… the sound often referred to as ‘flutter’ amongst many street-car enthusiasts!) and has been known to unwind turbo compressor wheels straight off the end of their shafts. (Note- these days most turbos incorporate a ‘reverse- locking’ nut to prevent against such unwinding issues. However, many turbo specialists will tell you that this has introduced a new issue. The locking nut is now forced to tighten under backpressure spikes and therefore places more stress on the cast compressor impeller, often leading to premature cracking and damage).

The biggest potential benefit of the BOV is that the entire turbo assembly will continue to spin at a high (potentially boost-producing) rpm almost the entire way through a gear shift. Throttle response should be the big improver on a BOV-equipped manual car, particularly in on/off driving conditions. (Perfect for Motorsport applications!) wink.gif

For superchargers BOVs are an even more critical item as even though the throttle is shut, the compressor mechanism will not not be stalled as the crankshaft is still driving it, and bloody hard! The pressure spikes that exist when the throttle is slammed shut on a blower can be enough to bend throttle butterflies like bananas. Ouch! Thankfully any supercharger kit worth its salt comes with a decent BOV system.

Remember one important point though. The need for a BOV only ever exists in a blow-through throttle-body turbo or supercharger system. The moment the throttle is placed on the front (intake) of any form of turbo or blower, the forced-induction device can spin quite merrily in vacuum the moment the throttle is snapped shut. This is because the charged air has a route to escape. (ie- the engine).

The BOV is nothing more than a valve that has an internal spring acting against the valve to equalize the boost pressure acting against the valve head. There is also a boost/ vacuum feed to the top of the BOV which, under boost conditions, assists the spring to hold the BOV closed. Under closed throttle, this reduces the spring pressure to and the vacuum helps pull the BOV open and let excess boosted air out. (There are some BOVs on the market that also function using an internal ‘diaphragm’ design. The boost/ vacuum feed line actuates this diaphragm in a similar way to achieve the same venting of excess boost pressure. Some argue that this type of BOV design is better due to greater sensitivity from the diaphragm itself (as opposed to a metal piston etc). However because of these intricacies, the downside being that wear and tear generally takes its toll much sooner with these style of BOVs as well).

Types

There are only a few simple factors to consider when buying a BOV. The main and most important is the size of the inlet and outlet orifices. As a rule, any performance application will need a minimum of 25mm size fittings. (All boost being equal, an inefficient BOV will often also be one of the most loudest on the market... this is due to the inlet and more commonly, outlet orifice being particularly small. Pressure escaping through such orifices makes for one loud sound, but very poor flow capabilities!).

Another consideration is adjustability, so that the spring pressure can be adjusted to stop any potential leaks at idle that can affect mass air-metered cars that don’t have a proper air-recirculation system (refer to diagram). The best way of fitting a BOV to any car equipped with mass-air or vane-type flow meter is with a proper recirculation system, which will allow a soft internal BOV spring setting. The lighter the spring tension, the more prone the valve will be to leakage, but better the BOV can perform its task. A light spring makes the BOV far more efficient and sensitive to small changes in throttle position and in some cases, the BOV will audibly vent air at some part throttle openings. Remember, the more spring tension you wind onto the BOV (with adjustable types), generally, the worse it will actually perform in preventing the compressor from stalling. (In many cases, those that adjust BOV tension to the highest settings often experience the sounds of cavitation or “flutter", indicating the BOV is working inefficiently … and thus may as well not be running a BOV at all!).

There are numerous different aftermarket types of BOVs available from various manufacturers (most of them Japanese, a few now Australian made as well) and with names such as ‘Super Sound’, ‘Super Sequential’, ‘Super Blow-Off’ etc. To some, how well a BOV works is not as important as the type of noise that it generates, with the characteristic “Ptshhhhh’ being a not-so-secret handshake amongst the, ‘I’ve got a turbo’ club!

Then there is appearance. I’m the first to agree that a BOV is normally a visual part of under bonnet presentation, something that anybody who enjoys their car will more than likely take seriously. However, to spend up to $700 on a polished and machined part that can be substituted for a $120 part with no discernable performance difference is sometimes hard to understand. The rule here is that if a BOV makes you feel good with the way it looks and sounds and it has adjustability and big vent areas, then by all means buy it. No-one other than jealous idiots will hang you for it!

Best Position

This is something I have mucked around with a lot over the years, trying to determine and then effectively work out a way to best measure how the placement of a BOV affects its performance. There is no easy way to do this other than by trying to rig up some sort of RPM transducer on the turbocharger shaft to see how placement affects the stall rpm amount. This is a difficult and arduous task to try and organize!

Logic would determine though that you would want to catch the biggest mass of pressurized air as close as possible to the point of reversion which, in this case, is the throttle body. Mounting the valve at an inclined angle to the throttle body so that air could exit cleanly at an angle could also bring additional efficiency. No-one seems to do this, which doesn’t mean they are right, maybe it’s worth a try. Nobody ever tried twin throttles on a four-cylinder before either!

Mounting the BOV close to the turbocharger compressor outlet is a little like shutting the stable gate after the horse has bolted. (Not to mention, the momentary time-lapse that would have to take place to ‘re-fill’ the pipe area between the turbo and throttle body… especially if you are running a front mount intercooler with extensive pipework?!).

Yet in the case of a constant-pressure system, like a turbocharger inlet tract, it may not make that much of a difference.

Installation

If you own a MAP sensor-equipped car there is no wrong way of setting up a BOV because you don’t have to recirculate the air like you do with an airflow meter-equipped car (more on that later). There is no way a BOV will affect tuning at all with a MAP sensor unless, or course, it is stuck open the whole time, in which case you will simply lose boost pressure.

Any engine equipped with an airflow meter is a different issue again and to be done, I suggest you have a look at the diagram supplied. The outlet from the BOV needs to be plumbed back into the inlet system after the airflow meter (upstream towards the engine) so that the airflow meter is not affected by the excessive air running around the inlet tract. Why? Imagine if you let the BOV vent to the atmosphere. As the BOV opens and lets out a mass of air, a corresponding amount is drawn straight back in through the turbocharger inlet (and hence airflow meter) which fools the ECU into thinking the engine was under load. When this false load signal occurs, the corresponding fuel mixtures are made super-rich. This usually results in frequent backfiring and in some cases, massive momentary flames firing out from the exhaust during gearshifts. Some love this, some don’t. (Particularly… Police!).

The other problem that occurs is the BOV being pulled open at idle if the spring setting is a little weak. If the system is not of the recirculating type and an airflow meter is installed, the ECU will normally enrichen the mixtures enough to cause the engine to stall. As a lot of aftermarket valves feature neat trumpets, and the like, to vent the BOV, there is no facility to return the air properly. (Although exceptions are now available in many cases these days). This then requires the spring tension to be tightened excessively to stop the valve from opening and the engine from stalling. In this instance you have simply compromised BOV performance for good looks and sound. Not recommended.

Better Performance?

I have tried repeatedly to measure the effect of the BOV on vehicle performance, not being able to pick a change with or without several types attached to several different cars. In fact, a workshop associate of mine goes as far as to say they are nothing more than a marketing ploy. I don’t know about that one. (Especially since BOVs are standard factory fitment these days, and to my knowledge most GT and WRC cars still employ them on race cars). This is where the problem lies. The BOV, although heavily touted as being a performance enhancer in some circles, is not designed to be primarily for this job. Always remember that the job of the BOV is to protect and enhance the longevity of the turbocharger. (Especially even more so with today’s turbocharger manufacturers who have ongoing development with ball bearing technology and a more recent focus on creating lighter compressor wheels with thinner blades!).

Conclusion

There is no doubt the BOV is a cool device. Any product that can look good, sound good and protect the life of the turbocharger must be good. Just don’t expect to reap some magical performance gain from the installation or upgrading of such a device. Measuring the results is almost impossible and, in some instances, you would think that they aren’t worth the expense for other than ‘show-pony’ value. If you buy the $700 device then maybe that is the case, but hey, if you do and you’re happy with it, who’s complaining?


*Article and diagrams taken from “Zoom” Performance magazine, issue No.26. Thanks also goes to Brett @ ‘Go Fast Bits’ for additional advice.
** Further editing in Italics by Pole Position crew

[evil1]

esssssssayyyy.......so what if you run no bov your car will run rich...hence the flames? cos i always thought bovs make u run rich...?

[Miami]

about halfway through...


Installation

If you own a MAP sensor-equipped car there is no wrong way of setting up a BOV because you don’t have to recirculate the air like you do with an airflow meter-equipped car (more on that later). There is no way a BOV will affect tuning at all with a MAP sensor unless, or course, it is stuck open the whole time, in which case you will simply lose boost pressure.

Any engine equipped with an airflow meter is a different issue again and to be done, I suggest you have a look at the diagram supplied. The outlet from the BOV needs to be plumbed back into the inlet system after the airflow meter (upstream towards the engine) so that the airflow meter is not affected by the excessive air running around the inlet tract. Why? Imagine if you let the BOV vent to the atmosphere. As the BOV opens and lets out a mass of air, a corresponding amount is drawn straight back in through the turbocharger inlet (and hence airflow meter) which fools the ECU into thinking the engine was under load. When this false load signal occurs, the corresponding fuel mixtures are made super-rich. This usually results in frequent backfiring and in some cases, massive momentary flames firing out from the exhaust during gearshifts. Some love this, some don’t. (Particularly… Police!).

[bodybodyrock]

very good read

[ReaperSS]

Since i put on BOV bumper gets alot blacker quicker,shows up bad on a white car and hard to keep clean.

[rxattak]

There's a reason turbo cars come with a BOV from factory. If it wasn't neccessary then manufactures wouldn't bother.

Having said that, loud BOV's piss you off about 1 week after you get them...


sorry to disagree but i believe there is a couple of cars that came from the factory with no bov

old skool f1 cars didnot run bov either do indy[i think] 40 50 psi no problems there but i reckon there turbos are heaps better than the china spec a lot of guys heer run

[upgarage]

haha who here runs a china turbo?

[Lonewolf]

sorry to disagree but i believe there is a couple of cars that came from the factory with no bov

old skool f1 cars didnot run bov either do indy[i think] 40 50 psi no problems there but i reckon there turbos are heaps better than the china spec a lot of guys heer run

yes some came without them, pretty much any turbo car from '88 onwards do however (as manufacturers caught on that they do have some benefits). If a car company could get away with no BOV, they would, as it would save 1000's of dollars over a cars production run.

race cars are a different story, theres numerous reasons for not running one (ie rally, they use antilag to keep the turbo spooled) especially the fact that turbo's are generally replaced after each race, negating the BOV helping turbo life.

[joey89]

race cars are a different story, theres numerous reasons for not running one (ie rally, they use antilag to keep the turbo spooled) especially the fact that turbo's are generally replaced after each race, negating the BOV helping turbo life.
Not only that they are hardly off the throttle and flat shift . . .

[SLEEKA]

sorry to disagree but i believe there is a couple of cars that came from the factory with no bov

old skool f1 cars didnot run bov either do indy[i think] 40 50 psi no problems there but i reckon there turbos are heaps better than the china spec a lot of guys heer run

old school f1 cars got torn down after each race, so $hit got replaced and the turbo only needed to last a short amount of time. We want a turbo to last 100k km + so a BOV will help to do this. At the end of the day some people love the sound or some hate the sound, thats why theres atmo or plumb back, but either way a BOV imho should be fitted. It helps eliminate or reduce compressor surge which in turn helps boost through gear changes and helps extend the life of the turbo, anybody that doesnt want those benefits shouldnt drive a turbo car... :hammer: