BOV blocked off?

[93 Eagle Talon TSi]

i know some of you are getting anoyed with my threads but im trying to get my post up past 30 and get my 30 days in so i can be a proven member, but i fix my reving up situation, kind of. the guy i bought the car from block off the bypass tube that goes to the maf plastic tube thats goes to the cold side of the turbo like in the picture, and some guy told me on here that this will kill my turbo and my intake, so im wondering how to fix this, because if i hook up a hose there the car will not rev up so do i need to buy a new maf? And again sorry for all the questions and my threads just trying to learn everthing i can from you guys.

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[93 Eagle Talon TSi]

the bov is a stock one. and the red one is the biggest one it goes to the maf tube that is connected to the cold side of the turbo, not the intake

 

[Gasolinebaptism]

Many BOV's, like greddy BOV's have a "trumpet" (outlet port) that screws into the housing.
Obviously, BOV's like the tial is a completely different design and therefore would require a replacement.

 

[cl1ckclack]

the MAF tube, and cold side of the turbo IS your intake.

 

[93 Eagle Talon TSi]

so should i buy an aftermarket bov

 

[Gasolinebaptism]

the bov is a stock one. and the red one is the biggest one it goes to the maf tube that is connected to the cold side of the turbo, not the intake

There is absolutely no reason for that tube being connected and sealed to have any adverse reaction to engine response and turbo spool whatsoever, what it should do is make it run better when the BOV is open (i.e. at idle, or between shifts), this is all assuming you didn't make the bonehead mistake of leaving that cap in line when you connected the tube.
It also sounds as if the tube isn't sealed. Maybe theres a hole in it somewhere, allowing unmetered atmospheric air to be brought into the intake past the MAF.

 

[H@xtGSX]

LMFAO.. God damnit.. I didnt notice that..

Best typo I have read in a long time... I was drinking a bit of vodka when I read that and nearly choked on it.

 

[Gasolinebaptism]

so should i buy an aftermarket bov

No, the OEM "green top" BOV is a good unit.

 

[cl1ckclack]

so should i buy an aftermarket bov

there is no reason to buy one... having one, just could have been a possible solution to what your issue is

 

[BurrowZ]

Remove cap from this:

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Now connect the red hose from the uncapped port to the big giant protruding horn on this(it's on the silver part, if you can't tell..):

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If it doesn't run still, check for holes in the hose you are using and make sure the clamps are tight.

 

[H@xtGSX]

Yup, easy as connecting those to things together...

 

[cl1ckclack]

Yup, easy as connecting those to things together...

hopefully its just that easy... but as we all know. most things arent when it comes to these cars

 

[93 Eagle Talon TSi]

@burrowZ

i did have that hooked up and it wouldnt rev up. thats why im so confused. if its capped it runs better and revs up. so thats why i was wondering if i need a new bov or a better one.

and i will check the hose for holes and clamp it better. will let you guys know tomarrow if i get to it.

hopefully its just that easy... but as we all know. most things arent when it comes to these cars

yep this is my first dsm and people told me how weird these cars are and im just now realizing it.

 

[BurrowZ]

@burrowZ

i did have that hooked up and it wouldnt rev up. thats why im so confused. if its capped it runs better and revs up. so thats why i was wondering if i need a new bov or a better one.

and i will check the hose for holes and clamp it better. will let you guys know tomarrow if i get to it.

The reason it's not revving up is because somewhere along that tract you are pulling in unmetered air (or losing it possibly) due to the hose not being tight enough or possibly torn. Any possible leaks your BOV would have can only be leaked into another part of the intake where it has already been metered, therefore you will still run just fine.

EDIT: And these aren't weird cars. They're just the same as any other car. Try modding other non-naturally aspirated cars with Mass Air Flow sensors in the same fashion and you'll get the same results. There are very few things that can stand out when it comes to DSMs but even that is debatable.

 

[H@xtGSX]

hopefully its just that easy... but as we all know. most things arent when it comes to these cars

I know... I am trying to lessen the initial shock.

Sounds like maybe your BOV is shot and leaking... Or a leaking hose.... Or whatever else might be allowing air into the system unmetered.

 

[93 Eagle Talon TSi]

The reason it's not revving up is because somewhere along that tract you are pulling in unmetered air (or losing it possibly) due to the hose not being tight enough or possibly torn. Any possible leaks your BOV would have can only be leaked into another part of the intake where it has already been metered, therefore you will still run just fine.

ok will check the hose tomarrow if i get to it. thanks guys.

I know... I am trying to lessen the initial shock.

Sounds like maybe your BOV is shot and leaking.

thats what i was think but if its capped, my car runs better so im more towards the leak in the hose

 

[H@xtGSX]

The intake pipe may be capped... What about where the BOV is? Is it functional? Is there one present?

 

[polarmoment]

You do need a BOV, or everytime you take your foot off the gas pedal, there will be a shockwave of air pounding the hell out of your turbo, trying to force it to spin the wrong direction. It will damage it eventually, unless you're running something with HUGE surge ports. Even then, it will eventually cause enough wear to damage it.

Actually, no. You don't need a BOV.

I've been running 20psi on a 20g TD06 daily for 5 years now without one and there is no sign of damage to my turbo (and I've disassembled it, looking for damage). There are a lot of internet and magazine myths surrounding the necessity of BOVs. That shockwave isn't much of a shockwave. It's a ~3psi pressure oscillation that descends the pressure scale as the charge decompresses through the compressor housing. Peak pressure never exceeds 5psi above nominal boost. Datalog the pressure trace once and you'll see what I'm talking about.

No actual "pressure" even acts on the compressor wheel. The pressure in the intake pipes is converted back to velocity as it moves backwards through the two diffusers (now acting as nozzles)- the scroll itself and the double wall at the exducer of the compressor. That velocity merely slows the velocity of air coming off the compressor wheel, causing it to stall. The impeller at full boost is spinning with the energy of an engine flywheel near redline. That's a LOT of gyroscopic force holding it in place, and rotational energy keeping it spinning. There's an oscillating load on the thrust bearing as the compressor grabs and slips the air, but:

This is happening with ALL of the thrust load from the turbine side removed. It's gone as soon as the throttle closes. On-throttle surge is what kills turbos. That oscillating load is negligible compared to the jet-engine thrust loads that come from the turbine side. Couple the two and that's when things start to die.

To paraphrase Corky Bell, author of Maximum Boost: "I don't think it's possible to damage a turbo by surging," referring to off-throttle surge and the use of BOVs as noise suppression devices.

BOVs are primarily a device to reduce the noise generated in the intake when the compressor goes into off-throttle surge (Mazda even directly states this in the repair manual for the RX7). There's some question as to the effect on emissions for hotwire MAF cars since they can measure airflow in both directions, but that's not relevant to karman MAfs. It's not a particularly damaging condition, as evidenced by the hoards of turbocharged prototypes in endurance racing throughout the 1980s and 1990s. And before you go saying "well, they change the turbo after every race..." keep in mind that a turbo takes more of a pounding in a 24 hour endurance race than an average street turbo takes in 10 years of service.

Now here's the real question- Why didn't (real, not "time attack") race cars use them, if they're supposed to be so instrumental in keeping the turbo spooled between shifts (another myth)?

Because they actually cost you spool. Turbochargers are positive feedback devices- the more boost you have, the more boost you make and the faster you make it until the wastegate steps in. Opening the throttle with 10psi left in the pipes re-spools the turbo literally twice as fast as having a BOV dump all that air out of the pipes, making you start over from 0. A BOV actually makes your car slower. On a roadcourse, it can cost literally full seconds per lap.

BOVs make cars go slower. That's why race cars don't use them. The difference on a fast shift without one vs. with one is very noticeable. It's the difference between waiting that split second for boost to come back and chirping the tires in the next gear because you already have full power.

Don't get me wrong, I'm not telling anyone to remove theirs. I'm just trying to point out the performance sacrifice OEM engineers made to quiet turbo cars down and make them more civilized to drive for the general public. A good example of this is the MR2 vs the Celica All-trac. The MR2, a mass produced, GT car came with a factory BOV to make the car more refined to drive. The All-trac, a race homologation special, did not come with a factory BOV. Same engine, same turbo. The car meant for consumption by the unwashed masses needed to be quieter. The car meant for enthusiasts did not.

Sorry to derail, just wanted to address this.

 

[bryanwheat]

BOVs make cars go slower. That's why race cars don't use them. The difference on a fast shift without one vs. with one is very noticeable. It's the difference between waiting that split second for boost to come back and chirping the tires in the next gear because you already have full power.

\

So you are telling me that the turbo being violently slowed down by the abrupt throttle body closing will maintain boost better than the turbo idling down with the air venting out the blow off valve. I am sure that the engineer's who design these cars weren't as smart as you huh. If you are running real fast times than you are either running an automatic or you are using no lift shift which would make the difference in having a bov and not having a bov totally irreverent because the throttle plate will never close anyways. Same thing on a road coarse, you would like be running no lift shift there when accelerating and only need to completely close the throttle when you are decelerating and going into a corner. Regardless if you are running a bov or not the turbo will be slowed down by the time you are back on the gas.

 

[dexterholland04]

It's almost too ironic that a MR2 guy posted that taking their BOV off was alright. A good friend of mine just did the same thing on his MR2...even after a whole discussion on why it wasn't such a good idea.

 

[Bud92gsx]

I'm sorry OP..I didn't mean to freak you out when I noticed the bov was not recirculated.

And I especially didn't mean it to turn into a 2 page thing.

http://www.dsmtuners.com/forums/fre...tions/113858-venting-your-bov-atmosphere.html
http://www.dsmtuners.com/forums/art...96-how-vent-your-blow-off-valve-properly.html

 

[polarmoment]

So you are telling me that the turbo being violently slowed down by the abrupt throttle body closing will maintain boost better than the turbo idling down with the air venting out the blow off valve.

Yes. And it's been confirmed via datalogging.

The loss in impeller speed is a function of the loss of drive pressure on the turbine and the distance of the rotating mass from the axis of rotation, not of reversion through the compressor housing. Seriously, think about this for a minute. Think about how much energy it took on the exhaust side (remember, you're adding fuel AFTER the compressor) to get to that speed. Now ask yourself just how much influence a pipe with a smaller PR and a fraction of the energy is going to have.

I am sure that the engineer's who design these cars weren't as smart as you huh.

Where did I ever imply that? What I'm saying is that their intention wasn't what you were taught to think it was. Their intention was to minimize the noise in the intake. Mazda has stated this, plain as day. If their intention was to save the turbo, why don't cars like the Lotus Esprit (both turbo 4 and V8 twin turbo) come with BOVs?

If you are running real fast times than you are either running an automatic or you are using no lift shift which would make the difference in having a bov and not having a bov totally irreverent because the throttle plate will never close anyways. Same thing on a road coarse, you would like be running no lift shift there when accelerating and only need to completely close the throttle when you are decelerating and going into a corner.

Actually, the turbo recovers about as fast with no-lift shift (standard style) as it does with a BOV in place. That's because the engine still ingests the air. Without a BOV, the charge pipes and intercooler act as a surge tank to store some of the boost so that there is actually BOOST in the pipes when you crack the throttle open again.

I'm saying this as someone who abandoned no-lift shift (ignition cut) when I realized it wasn't any faster. The only no-lift shift that would actually work as you say it would is the type that pulls massive timing to keep the fire burning through the turbo even while the engine is decelerating for the next gear. This is the type that indycars and LMP cars use. They don't just shut off the fuel or ignition because it still slows the turbo down at almost the exact same rate as closing the throttle.

You're also ignoring the massive effect it has on balancing the car with the throttle. Instead of dumping the intake charge every time you breathe the throttle around a long corner, the car has much more linear response and acts more like an N/A car. Maybe that's not all that important with an AWD car, since it doesn't require the finesse that a RWD car does to drive fast. In any car that suffers from even the mildest trailing throttle oversteer, it's a HUGE benefit.

Regardless if you are running a bov or not the turbo will be slowed down by the time you are back on the gas.

You're missing the point. I'll state it again so it's clear: Turbochargers are positive feedback devices. The more boost you have, the more boost you make, and the faster you make it until the wastegate steps in. Really think about that. 10psi in the charge pipes when the throttle opens will always build boost faster than 0psi, even if the impeller is spinning a negligible amount slower. This is a fact known by race engineers since the 1980s. It's the misinformation by manufacturers trying to sell unnecessary stuff that has kept the performance community blindsided for so long.


People use words like "air SLAMS into the compressor.." and that really shows that they don't have a firm grasp on what's actually happening. There are even people out there who still believe the impeller stops or spins backwards!

It's almost too ironic that a MR2 guy posted that taking their BOV off was alright. A good friend of mine just did the same thing on his MR2...even after a whole discussion on why it wasn't such a good idea.

I'm the guy that started the discussion in the MR2 community. I got pretty much the same response there for a number of years until people started investigating this for themselves and found that I was right. It's actually pretty common in Japan, Australia, and Europe to delete the BOV. They don't have failures. We've yet to have a failure. I believe the Crawford subaru turbo/IC kits come without provision for a BOV, and they don't seem to think it's a bad idea- because they're catching on.

Like I said, I'm not telling you to do it. I am, however, asking you to do some actual research on the subject before you go telling someone "what a bad idea it is." If people actually educate themselves, we can eradicate this bullshit myth once and for all.

The fact of the matter is, however, that there are a lot of people out there who are very knowledgeable about turbo cars in general, but still don't have a firm grasp on how turbochargers actually make boost. The compressor wheel does not make pressure by cramming air in (that would be a positive displacement pump- like a supercharger). It makes pressure by pulling air in, increasing its velocity, then slowing the air back down again. When slowing the air down, the energy added is converted to static pressure. There are a lot of aerodynamics involved between the exducer of the compressor wheel and the outlet of the compressor housing, and people talking about "violent waves slamming into the wheel" very obviously don't understand those aerodynamics.

Then again, maybe I shouldn't be telling people this. Let them leave a couple seconds per lap on the table because they don't know any better.

 

[93 Eagle Talon TSi]

The intake pipe may be capped... What about where the BOV is? Is it functional? Is there one present?

i know its functinal because i stuck a rag in the bov big hole and when i let the throttle go it shot out and made the tis sound so im sure its working.

 

[bryanwheat]

It could still be leaking, do a boost leak test and find out.

 

[93 Eagle Talon TSi]

i dont have one so i will have to go buy one.

http://www.dsmtuners.com/forums/art...96-how-vent-your-blow-off-valve-properly.html

in this post it say not to vent my stock bov to the maf so isnt that what you guy are telling me?

 

[bryanwheat]

i dont have one so i will have to go buy one.




in this post it say not to vent my stock bov to the maf so isnt that what you guy are telling me?

That thread is telling you what you need to do to be able to vent the bov. As you can see you have to have a gm maf after the bov, or run speed density. That thread doesn't pertain to you, your car, or anything that you need to do. You can make a boost leak tester for around 10-15 bucks with supplies from home depot or and hardware store.