Question Regarding Blow-off Valves

[Dead_Poetic]

Hey everyone, Just recently a good friend of mine bought a 2004 Volkswagen Jetta GLI. Being that its turbocharged, He really wants to get a blow off valve for it, pretty much just to have that cool sound. He asked a different friend of ours (he also has a gli) and he said not to put a blow off valve on it because it causes you to lose horsepower. Is this true?

 

[buickgnx88]

He really wants to get a blow off valve for it, pretty much just to have that cool sound.

 

[bergauk]

Yes its true, or from what I understand from talking to my brother. Blow-off Valves essentially open up a bypass for the exhaust to go through past the turbo. There is some pressure lost through that process. Pressure loss = less horsepower, but less of a chance that you'll destroy your turbo. Either way its up to your friend on whether or not he wants that cool sound.

 

[ExigeEvan]

At least he's upfront about it. And lets be fair, there's plenty of other members on this site who do things for other than performance reasons to their car, and I don't see most people complaining.

 

[Dead_Poetic]

At least he's upfront about it. And lets be fair, there's plenty of other members on this site who do things for other than performance reasons to their car, and I don't see most people complaining.

Thanks. Lets be honest, its not more trivial then getting any visual upgrade. And at least it can have benefit, especially if he decides to upgrade to a stage two or beyond.

Another question though: If he does put on the blow-off valve, about how much of a horsepower loss are we looking at?

 

[sesselpupser]

Probably depends on the valve, the more pressure it bleeds off the more is lost, basically the louder the sound the more pressure is let out so the more power it loses. Then again I was under the impression that blow-off valves and wastegates are different, blow-off valves being the ones that work when the turbo is on-boost to alleviate some of the pressure and wastegates only working when the turbo comes off-boost, i.e. when you take your foot off the accelerator (like, say, when changing gear) to immediately empty any pressure left in the turbo. Then again I have also heard that these are the same things, which I'm more inclined to believe, but surely if a wastegate/BOV only really dumps the pressure when you're not accelerating, why would it matter if the horsepower is down?

In other words, if he got a blow-off valve that was closed while his foot is down on the accelerator and no pressure is let off while the turbo is on boost (seems pointless to do that on a stock car, though, since the pressures will be well within the tolerances of the engine and turbo, but then again I think most turbos have one as standard) but opens when he takes his foot off the accelerator, then he wouldn't have any horsepower lost through bled-off pressure but would get the cool woosh sound.

Also its worth pointing out that you can get valves that dump the exhaust gas into the exhaust plumbing and others that dump it directly into the atmosphere, which I would imagine gives a better sound and releases the pressure instantly.

That was the least coherent post I've ever written but, well, deal with it


p.s. if his car already has one, which it probably does, he could probably just modify it to make the sound anyway, not much point spending the money on a performance part if its going to be bolted on to the standard car... Maybe if he goes mad and tries to get 400bhp+ out of it then yeah, by all means, but if its otherwise standard, just, I dunno, glue a whistle to the existing one

 

[Perfect Balance]

Yes its true, or from what I understand from talking to my brother. Blow-off Valves essentially open up a bypass for the exhaust to go through past the turbo.

That would be the wastegate. The blowoff valve lets the extra air out of the intake portion.


I'm not sure how much of a power difference it makes, since the wastegate is what controls the actual psi of the turbo, but it would change the response of the engine.

Basically, with a blowoff valve set to go off under more pressure, you end up with more air left over in the piping for when you open the throttle again, aiding with response, but putting more stress on your turbo. If you have it set to let off under less pressure, you do less damage to your components, but response goes down. That's all the info I can provide.

EDIT: A wastegate is normally a spring operated valve that gets forced open by exhaust gasses at a certain pressure, bypassing the exhaust portion of the turbo and re-routing into the exhaust. This is what keeps your engine at a certain psi.

EDIT #2: You can also have boost creep, which is when the wastegate is fully open but still doesn't let the gasses flow out quickly enough, so the pressures just keep rising slowly. This would normally happen in long duration conditions, like accelerating in 5th gear.

 

[Rotary Junkie]

Never mind, remind me to refresh next time >.<

 

[HACKr]

http://www.streetracersonline.com/articles/turbo/bov.php

 

[Dead_Poetic]

Okay, thanks a lot for the help guys. Anything else I should know?

 

[DriifterX]

You wont notice any loss of power, if any power is lost it'll be an extremely small amount. If however this is a worry, you could set up a plumb back set up so that the air from the blow off valve is 'fired' back into the intake. My friend did this on his evo 6 and he reckons it stopped a bit of lag between gearshifts

 

[L_Hamilton]

MKIV Jettas = Diverter Valve.

 

[Slicks]

Hey everyone, Just recently a good friend of mine bought a 2004 Volkswagen Jetta GLI. Being that its turbocharged, He really wants to get a blow off valve for it, pretty much just to have that cool sound. He asked a different friend of ours (he also has a gli) and he said not to put a blow off valve on it because it causes you to lose horsepower. Is this true?

I'm not sure how air is metered in VW's (2.0T? 1.8T?) powerplants, but it's most likely not a good idea.

It won't cause a loss of horsepower, per se. However, you are (again, depending on how and where the air's metered) letting out compressed air, and typically recirculating it into the intake, pre-turbo. This air has already been accounted for by the computer, and letting it out into the atmosphere means that you've now got XX amount of air less than the computer thinks is there. It'll cause a rich condition.

Overall... just inefficient. Some forced induction vehicles are designed in a way that puts the MAF/MAS/MAP/ETC after the turbo, and it is then usually optional of whether you recirculate or vent to atmosphere.

 

[slidesquad#1]

From what I've heard, going with a VTA blow-off valve in a VW is generally a bad idea. A recirculating one would probably be fine, but wouldn't provide the mad tyt3 sound effektz.
Personally, I wouldn't do it.

 

[Keef]

And replacing the stock recirculating valve with an aftermarket one would be pointless unless the stock one failed, in which case the aftermarket one would probably be cheaper assuming the car isn't under warranty.

I believe Race Idiot was telling me that on his second gen MR2 turbo it's recommended that you keep a recirculating valve. Apparently when it vents to the atmosphere it causes the engine to run very rich for a split second. I guess the computer's response on the fuel side is delayed behind the throttle pedal's, so when the computer is expecting there to be air present and it isn't, it doesn't compensate. It's programmed to delay, and when it doesn't receive the air from the BOV it still squirts in the fuel, causing a very rich mixture.

Something like that. I've personally seen many turbo cars with a VTA valve blow a rich plume whenever teh driver lets go of the throttle. It wouldn't do that with a recirculator.

 

[Omnis]

Just get an electronic BOV sound machine.

 

[Racer XO]

The question is how is the turbo currently setup... i.e is it internally gated? if so installing a blow-off valve will require some modification to change it to a blow thru setup and as was alreacdy mentioned having a gated setup will not cause a loss in hp

 

[benzoboy]

Wow, you're helpful.

You're saying every modification that should be done to a car has to improve performance? I'll give you stick if you ever decide to re-paint a car, add stickers or change the rims. Among others.

OT: I'm no car expert, but I heard that what a BOV does is stop air flow in the turbo for a split second, then releases it quickly (Hence the 'whoosh' sound.). I also heard that this causes a decrease in turbo performance, which probably would result in lower HP levels, not by too much though.

Another disadvantage I hear of is a decreased turbo life, it seems restricting the air flow is bad for the turbo unsurprisingly.

Personally, I'd get one, 'cos BOVs sound awesome. I recommend a HKS SSQV.


They're on Supras, so I guess they'd probably make it sound better somewhat, with that bad-ass engine sound. But you get the point.

Hope this helps.

 

[McLaren]

Wow, you're helpful.

You're saying every modification that should be done to a car has to improve performance? I'll give you stick if you ever decide to re-paint a car, add stickers or change the rims. Among others.

He's not saying modifying anything else but performance is silly, but the reason the guy wants a blow off vale is silly. And I agree. I'd buy a blow off valve to use it for what it is intended for, not because it goes, "PSHHH!!!" I wouldn't be surprised if this guy wants one just so he can rev at stoplights and make noise with it.

If he wants his car to sound cool, try doing what the majority of kids here do to their Camaros & Mustangs, and just buy a new exhaust....

 

[Dead_Poetic]

He's not saying modifying anything else but performance is silly, but the reason the guy wants a blow off vale is silly. And I agree. I'd buy a blow off valve to use it for what it is intended for, not because it goes, "PSHHH!!!" I wouldn't be surprised if this guy wants one just so he can rev at stoplights and make noise with it.

If he wants his car to sound cool, try doing what the majority of kids here do to their Camaros & Mustangs, and just buy a new exhaust....

Lets be honest, having that sound is cool, it sets your car apart from every other stock gli out there, and its just a nice little touch. AND, please understand that if he knew it would cause his car to run lean, or cause any damage at all to his car, he wouldn't do it. Hence the reason why I am trying to figure out any benefits and or repercussions that may result. Plus, he wants a genuine way to make his car sound cool, he doesn't want some obnoxiously loud and annoying fart can because they usually don't help much with performance, and are very ugly. He is a lot more concerned about performance than he is with looks, which is one of the reasons why he bought the gli-it looks very clean and modified even stock. Do not question his motives, and since you are NOT contributing to this thread, get out. I do not want your opinion.

To everyone else who is actually giving constructive criticism, thank you, and I will definitely be forwarding this information to him.

 

[buickgnx88]

Lets be honest, having that sound is cool, it sets your car apart from every other stock gli out there

Sounds like that "fast and the furious" mindset.

Do not question his motives, and since you are NOT contributing to this thread, get out. I do not want your opinion.

Can do chief!

 

[95GTIVR6]

I have a turbo vehicle and I think the stock bypass valve is loud enough. In stock form, you can barely make out the sound, with a K&N drop in it is more audible. I put on a Cold Air Intake and the sound increased but when I put on a Turbo Inlet pipe, the sound decreased.

Tell your friend that all sounds do to your car is draw more attention. There are other things he could do with $200.00. Stay stock, or as close to it as you can.

 

[slidesquad#1]

Personally, I'd get one, 'cos BOVs sound awesome. I recommend a HKS SSQV

I have one of these, it was installed by the previous owner. Mine is stupidly loud, even with the standard intake system. I shudder to think of how deafening it will be if I decide to get a CAI. It's cool for a laugh initially, but it gets real tiring after a while.

On another note, what else has been done to the VW, if anything at all?

 

[Turbo_G54B]

My car didn't come with a BPV/BOV, so it would make a turkey gobble sound (compressor surge) before I put one in.

Personally, I really like hearing mine sound off. Mine isn't too loud or high pitched. I hate the high pitched ones

The one I have:

HKS Racing Bypass Valve

So to summarize what's been said:
Blow Off Valve - Vents the excess boost pressure to the atmosphere. Causes your car to run rich (more fuel than air) for an instant, since it is releasing air that the computer still thinks is in the system. Any loss in horsepower from this would probably be unnoticeable.
Bypass Valve - Recirculates the excess boost pressure to a location before the turbo, and all the air remains accounted for, so no richness.

The problem with running a turbo settup without a BPV/BOV:
"If you are running 15psi boost and slam the throttle shut the boost pressure spikes up and tries to drive the compressor wheel backwards into the Turbo. This does 3 things...

First...it stalls the Turbo so that when you open the throttle back up it has to spool up allover again causing lag and hesitation.

Second...It puts a terrible load on the thrust bearing of the Turbo which can cause premature wear and failure.

Third...It weakens all your soft connections in the intercooler plumbing from excessive expansion and contraction."

 

[McLaren]

Lets be honest, having that sound is cool, it sets your car apart from every other stock gli out there, and its just a nice little touch.

But that shouldn't be the reason you want or need one. I'm positive manufacturers don't build blow off valves so they can make noise.

AND, please understand that if he knew it would cause his car to run lean, or cause any damage at all to his car, he wouldn't do it. Hence the reason why I am trying to figure out any benefits and or repercussions that may result.

That's fine. Some of us still think it is a silly reason to want one.

Plus, he wants a genuine way to make his car sound cool, he doesn't want some obnoxiously loud and annoying fart can because they usually don't help much with performance, and are very ugly.

That's fine, but there are other ways of changing the sound.

He is a lot more concerned about performance than he is with looks, which is one of the reasons why he bought the gli-it looks very clean and modified even stock.

He wants performance instead of looks, yet the only reason he wants a BOV is to make noise so people will notice? Ok, that sounds quite a bit contradicting....

Do not question his motives,

I'm positive I have the right to question anyone's motives. I think wanting a BOV for its sound is silly.

and since you are NOT contributing to this thread, get out. I do not want your opinion.

I love this defense. You made the thread, so you believe you are automatically entitled to who & who can't make a post just because you don't like the response. Unfortunately, doesn't work that way bud.

You brought up the topic that your friend wants a BOV just for the sound, so I'm gave my opinion regardless of whether or not you care.

 

[Holdenhsvgtsr]

Personally, I'd get one, 'cos BOVs sound awesome. I recommend a HKS SSQV.


They're on Supras, so I guess they'd probably make it sound better somewhat, with that bad-ass engine sound. But you get the point.

Hope this helps.

They are only good if your shifting a serious amount of power/boost. A friend of mine had one on his leon cupra (wasnt standard,had a K04 hybird now a GTRS) and it kept messing with the engine management. They are also annoying like hell after 30mins the novelty wears off very quickly.

 

[Dead_Poetic]

I love this defense. You made the thread, so you believe you are automatically entitled to who & who can't make a post just because you don't like the response. Unfortunately, doesn't work that way bud.

You brought up the topic that your friend wants a BOV just for the sound, so I'm gave my opinion regardless of whether or not you care.

I dont think that because I made the thread I can kick people out of it, I just hate it when veterans of this forum act like they can say remarks that contribute nothing at all to the thread, or the issue at hand and think it justified. I created this thread to get positive feedback on the negative and positive effects of installing a blow off valve; not to have you come in here and ruin the thread.

And thanks to all of you who did give me real reasons why or why not to install one, and because of it he has decided to not install it. He was under the impression that it was a very easy mod that didn't really effect performance either way. And as such, why wouldn't you install it, provided you like the sound. But now he knows, and definitely will not be installing it. Hes now looking at some other cheap mods that are much more efficient.

 

[Azuremen]

Well, that's good. Its pretty funny to watch a car with "mad tyte BOV" sound that accelerates like a stock car.

About the same as a Honda Civic with a glass pack and that's it. Noisy.

 

[McLaren]

I dont think that because I made the thread I can kick people out of it, I just hate it when veterans of this forum act like they can say remarks that contribute nothing at all to the thread, or the issue at hand and think it justified.

So the thread automatically has to be only filled with responses answering your question? Or that the community is not allowed to give their opinion?

That's quite ridiculous. Whether or not you wanted feedback on your question, you should have expected any other kind of response, esp. when you're telling the forum the only reason this guy wants a BOV is for noise.

I created this thread to get positive feedback on the negative and positive effects of installing a blow off valve; not to have you come in here and ruin the thread.

I came in here defending buickgnx because he was misunderstood by benzo. I also said that I agreed wanting a BOV was silly. You went on the defense instantly, spouting that your friend is all about performance and what not. Then you told me to get out just because I expressed that wanting a BOV for its noise is stupid.

If you couldn't handle the criticism about why the guy wants a BOV, then you shouldn't have even brought up that fact. I'm amazed nobody has called him a ricer yet for just wanting to make noise.

 

[Frizbe]

I dont know if anyone will actually read this post, and the info I provide might have all ready been covered but I'm in a hurry sooo....

The MKIV A body turbo engines use a MAF, with the meter placed right after the air filter, if you put a Atmospheric BOV on said vehicle, the dis-charge is, of course, vented out and is no longer in the system. HOwever the VW's ECU still thinks that air is in the system, when its not, meaning the vehicle starts to run rich. Because the ECU is dumping in more gas for no-more air. AFIK most A-BOV can be purchased with an add-on that converts it to a Recirculating BOV, or diverter valve. that said the only way to really hear the DV is to get an intake. which with an intake you can hear the stock DV, so there is really no reason to get an aftermarket DV unless the vehicle is reflashed.


PS I would recomend the REVO reflash and a Forge 007 DV.👍