BOV noise

[Breezy]

When does the BOV make a noise?

[tRipitaka]

when throttle is released..

[b18c_crx]

when boost comes on and when u release the throttle

[Zdster]

Reopened. Plus PQ points all around :thumbsup:.

[DLO01]

when boost comes on and when u release the throttle

To confirm and as I think this is what your trying to say.

Your BOV 'blows off' when there is +ve pressure in your charge piping and -ve pressure in your intake manifold, separated by the closed butterfly (off throttle changing gears).

A BOV maintains the Turbo spooled up (spinning) ready for when you get back on the throttle again.

If you did not have a BOV and your close the butterfly (off throttle changing gears), +ve pressure in the intake will escape back through the turbo slowing it down.

[string]

To confirm and as I think this is what your trying to say.

Your BOV 'blows off' when there is +ve pressure in your charge piping and -ve pressure in your intake manifold, separated by the closed butterfly (off throttle changing gears).

A BOV maintains the Turbo spooled up (spinning) ready for when you get back on the throttle again.

If you did not have a BOV and your close the butterfly (off throttle changing gears), +ve pressure in the intake will escape back through the turbo slowing it down.
Most people have their blow off valve located on the cold side charge piping anyway so you'll have half of your charge going back through the turbo anyway. Also, you'll get nowhere near maintaining shaft speed, due to the fact you are removing the driving force on the turbine (exhaust).

[DLO01]

If your Bov is opperating and working correctly, you will not get flow back through the turbo. This is the whole purpose of a Bov. If you Bov is open its releasing air, therefore the turbo can maintain flow, spooled up ready for boost once the butterfly opens.

If you can hear flutter. That is boost going back/reverse way through the compressor wheel. Either your Bov is adjusted too tightly and is not opening, installed incorectly or you have no Bov at all.

The reverse flow through the turbo heard by this flutter will slow your turbo and put extra pressure on the turbos bearings.

[string]

How on earth do you think a turbo can maintain flow against a closed throttle, with no force driving the compressor?

The whole reason the flutter noise exists is because the turbo can't maintain flow; thus it surges due to pressure in the charge piping and it's inability to maintain that pressure. By removing the pressure in the charge piping, it changes nothing in the compressor, except an unproven myth about thrust bearing damage from the insignificant ammount of surge you get.

[DLO01]

How on earth do you think a turbo can maintain flow against a closed throttle, with no force driving the compressor?

The turbo is still spinning a million miles an hour, 'before' you take the throttle off (butterfly open). Once you take your throttle off (butterfly closed) the Bov opens alowing it to continue to spin a million miles an hour as there is no boost against/pushing reverse way against the compressor, therefore maintaining flow and can make boost as soon as the bov closes for the next throttle application. Make sense?

[Muzz]

How on earth do you think a turbo can maintain flow against a closed throttle, with no force driving the compressor?

It does so with momentum, turbos spool up too 100,000 rpm. The amount of time your off the throttle to change gears may be half a second, the only way the turbo will stop spooling, is if there is a massive pressure build up extremly quickly from not having a bov.

When you let off the throttle the bov opens and the air can continue to flow without building to much pressure, since there is no huge restriction for this air pump, it will continue to spin, there may be nothing really driving it as you say, but there is nothing really providing a huge resistance trying to slow the turbo spool rate either. Half a second isnt enough time for the turbo to stop spinning, when there isnt much trying to stop it, and its spinning incredibly fast.

[string]

The turbo is still spinning a million miles an hour, 'before' you take the throttle off (butterfly open). Once you take your throttle off (butterfly closed) the Bov opens alowing it to continue to spin a million miles an hour as there is no boost against/pushing reverse way against the compressor, therefore maintaining flow and can make boost as soon as the bov closes for the next throttle application. Make sense?
No it doesn't.

A turbo spinning at "a million miles an hour" pushes a huge chunk of air. Compression comes at a price, energy cost. This energy comes from pressure on the turbine. The instant you release the throttle, you no longer have any energy being applied to the compressor. It's rotation instantly becomes resistance as it is trying to compress air with no drive. It slows down immensely.

A blow off valve is only there to remove pressure in the charge piping so that the compressor does not surge. Maintaining flow is a load of crap. That's what anti-lag on rally cars does, not blow off valves. To maintain flow you need continuous energy input. Delayed combustion event into the turbine does this. Reduction of compressor output resistance does not.

[Muzz]

Most people have their blow off valve located on the cold side charge piping anyway so you'll have half of your charge going back through the turbo anyway.

the bov is always between the turbo and butterfly, it sohuld release most of the pressure with very vert little, if any, going back through the turbo.


Also, you'll get nowhere near maintaining shaft speed, due to the fact you are removing the driving force on the turbine (exhaust).

the turbo may have half a second where it isnt really driven by exhaust, this isnt long enough to reduce the turbos extream rpms, being that there is not much resistance trying to stop it from spinning, as the pressure after the turbo is being released by the bov.

[DLO01]

It does so with momentum Agreed.

[string]

the bov is always between the turbo and butterfly, it sohuld release most of the pressure with very vert little, if any, going back through the turbo.

Obviously. I was saying that it is usually very close to the throttle. Just because the blow off valve opening has a lesser resistance than the compressor, does not mean that all the air simply goes out of it. What do you think happens to the air closest to the compressor? It gets sucked all the way back to the blow off valve?



the turbo may have half a second where it isnt really driven by exhaust, this isnt long enough to reduce the turbos extream rpms, being that there is not much resistance trying to stop it from spinning, as the pressure after the turbo is being released by the bov.
It's plenty of time to reduce the rpm of the shaft. The power required to maintain a given pressure ratio is substantial relative to the power generated by the charge. What makes you think that when you take away the driving force that it's going to be happy to sit at "extreme rpms" for half a second? It is a compressor not a fan, it's resistance in the air is massive, especially at high shaft speeds where you actually get charge compression.

[tRipitaka]

i've heard, if the BOV is closer to the throttle/intake manifold, performance/response is better..
but if the BOV is closer to the turbo, the life of the turbo is increased..

anyone want to shed some light on this ?

[string]

Agreed.

I'd agree with the both of you if the compressor was actually a solid steel cylinder. Unfortunately, it isn't. Momentum is all well and good, until you realise you have a compressor trying to compress a full flow rate's worth of air without aid.

Now I won't bring any calculations into this, because we all know that no one likes those, but i'd hazzard a guess to say that the kinetic energy of a fully spooled turbo shaft, turbine and compressor, will be negligible compared to the energy requirement of half a second's worth of compression.

[string]

No I am talking about an atmospheric releasing blow off valve.


i've heard, if the BOV is closer to the throttle/intake manifold, performance/response is better..
but if the BOV is closer to the turbo, the life of the turbo is increased..

anyone want to shed some light on this ?
There is no evidence to support that even having no BOV even affects turbo life. Of course running a compressor continuously in the surge region is not good for bearing life but you'd have to be mad to run a setup which does this.

[Muzz]

No it doesn't.

A turbo spinning at "a million miles an hour" pushes a huge chunk of air. Compression comes at a price, energy cost. This energy comes from pressure on the turbine. The instant you release the throttle, you no longer have any energy being applied to the compressor. It's rotation instantly becomes resistance as it is trying to compress air with no drive. It slows down immensely.


Thats the point of a bov, so that it it isnt compressing air while your off the throttle. That air is being released.

A turbo spinning at 100,000rpm, say you let off the throttle for half a second, for the turbo to drop to say 70,000 rpm over that time, its rpm will have to decrease at 60,000 rpms in a second. This is not going to happen, momentum wont allow it unless there is a big force working against it, somthing that the bov gets rid of.




A blow off valve is only there to remove pressure in the charge piping so that the compressor does not surge. Maintaining flow is a load of crap.

Incorrect. Yes the bov is there to remove air pressure in the charge piping. Doing so helps the compressor keep its spool up while off the throttle, by stopping the compressor surging. Compressor surge is what suddenly decreases the shafts rpm, removing the surge against the compressor, means the shaft will decelerater ALOT slower. And as im sure you know, air is flowing, when the turbo is spinning.




That's what anti-lag on rally cars does, not blow off valves. To maintain flow you need continuous energy input. Delayed combustion event into the turbine does this. Reduction of compressor output resistance does not.

Anti lag drives the turbo while off the throttle, this keeps it spooled.
The bov releases pressure after the turbo, while off the throttle, the stop the turbo from suddenly decelerating from surge, the momentum keeps the spool from dropping fast.




To maintain flow you need continuous energy input.

Or you need to reduce the resistance created when not providing energy, so that the shaft decelerates at a much much slower rate. This is the purpose of a bov.

[string]

You missed post #16?


Thats the point of a bov, so that it it isnt compressing air while your off the throttle. That air is being released.

A spinning compressor will always be trying to compress. The blow off valve does not reduce the space around the compressor to a pure vacuum despite what you might think.


A turbo spinning at 100,000rpm, say you let off the throttle for half a second, for the turbo to drop to say 70,000 rpm over that time, its rpm will have to decrease at 60,000 rpms in a second. This is not going to happen, momentum wont allow it unless there is a big force working against it, somthing that the bov gets rid of.

Momentum does allow it. The rotating assembly of a turbo is made to be as light as possible such that it can spool as fast as possible. The blow off valve does not remove any of the resistance on the compressor. It is still trying to compress with no power being applied. The blow off valve is pretty much equivilent to opening the throttle but disconnecting the engine from the turbing housing. You're pumping air into something which is giving nothing back to you. It's going to slow down like a mofo.



Incorrect. Yes the bov is there to remove air pressure in the charge piping. Doing so helps the compressor keep its spool up while off the throttle, by stopping the compressor surging. Compressor surge is what suddenly decreases the shafts rpm, removing the surge against the compressor, means the shaft will decelerater ALOT slower. And as im sure you know, air is flowing, when the turbo is spinning.

There are far more things to stop a compressor shaft than surging or stalling. Of course air is flowing when the turbo is spinning. Moving air requires WORK. Under normal operation, that work is provided by input to the turbine. When you take away the input to the turbine where does the energy for the work on air come from? Kinetic energy of the rotating assembly. The more air you want to push off throttle, the faster your going to slow down the turbo shaft. It's fundamental physics; conservation of energy. You learn it in high school.
[/quote]


Anti lag drives the turbo while off the throttle, this keeps it spooled.
The bov releases pressure after the turbo, while off the throttle, the stop the turbo from suddenly decelerating from surge, the momentum keeps the spool from dropping fast.

See above.



Or you need to reduce the resistance created when not providing energy, so that the shaft decelerates at a much much slower rate. This is the purpose of a bov.
See above again.

The primary purpose of a BOV is to make the manufacturers a lot of money. If you have a link to evidence of BOV's doing any of the above to a tangible level please let me know. The majority of people who use them do so for the sound, or because they think that it will destroy their turbo otherwise. Not because they made a logical conclusion themselves, but because they were told so by other sheep.

[Muzz]

Obviously. I was saying that it is usually very close to the throttle. Just because the blow off valve opening has a lesser resistance than the compressor, does not mean that all the air simply goes out of it. What do you think happens to the air closest to the compressor? It gets sucked all the way back to the blow off valve?
The air thats closest to the compresser gets pumped down the piping and out of the bov




It's plenty of time to reduce the rpm of the shaft. The power required to maintain a given pressure ratio is substantial relative to the power generated by the charge. What makes you think that when you take away the driving force that it's going to be happy to sit at "extreme rpms" for half a second? It is a compressor not a fan, it's resistance in the air is massive, especially at high shaft speeds where you actually get charge compression.

Yes the resistance is high.
No it wont be happy to sit at extream rpms, it will decelerate with no driving force.

What i am trying to explain to you is that by releasing the pressure from building up after the turbo when the throttle is shut, the compresser shaft will decererate alot slower than if there was nowhere for the compressed air to flow and it surged the compressor.

The spool might decelerate from 100,000rpm to 70,000 rpm over half a second with a bov to stop pressure build up and surge.
The spool might decelerate from 100,000rpm to 10,000 rpm over half a second if there is nowhwere for the compressed air to flow, and it surges the compressor, causing it to stall.

[DLO01]

There is no evidence to support that even having no BOV even affects turbo life. Of course running a compressor continuously in the surge region is not good for bearing life but you'd have to be mad to run a setup which does this.

Very good discussion guys.

Sorry, I don't mean to target you, but I disagree with this. The pressure (boost) in the charge pipes during butterfly closed is opposing the compressor wheels normal direction. So therefore they are both resisting each other. Opposite forces will have an affect on each other. The boost against the compressor wheel with cause a shear force on the shaft and added pressure on bearings. It may not be much, but still its more force then if you did have a Bov.

[string]

Very good discussion guys.

Sorry, I don't mean to target you, but I disagree with this. The pressure (boost) in the charge pipes during butterfly closed is opposing the compressor wheels normal direction. So therefore they are both resisting each other. Opposite forces will have an affect on each other. The boost against the compressor wheel with cause a shear force on the shaft and added pressure on bearings. It may not be much, but still its more force then if you did have a Bov.
This is true. But it's like saying that if you have cancer, scraping your knee will kill you faster than if you didn't do it. It's adding a nill insult to injury. Awful example but you get the point :)

Imagine how much of the same type of pressure is on the shaft under normal operation? Far more than the 100grams of air you have in your charge pipes pushing against it. The act of compressing air creates the same forces as the ones you described above.

You primarily get wear from surge, not air pushing on the compressor. And until someone provides a link with some solid evidence supporting tangible wear from no blow off valve, this is a moot point.

[DLO01]

Points all round for good discussions. :thumbsup:

[Muzz]

You missed post #16?

A spinning compressor will always be trying to compress. The blow off valve does not reduce the space around the compressor to a pure vacuum despite what you might think.



lmao, let me ask you this.
If you take a turbo and run exhaust through it, does it compress air if no charge pipe is connected to the outlet?
Answer: NO, it pushes air, it is a pump. The air gets compressed when the air being pushed into the intake cannot be ingested fast enough.

So if the bov opens the air being pumped has somwhere to escape, instead of having nowhere to escape and building massive pressures in an extremly quick amount of time. This would take energy from the shaft at a very very fast rate, stalling it in no time.

Do you agree up to here?

Would you agree that massive pressure build up, when there is nothing driving the shaft, is what causes surge, and even stalling of the compressor?


Momentum does allow it. The rotating assembly of a turbo is made to be as light as possible such that it can spool as fast as possible.


Momentum is a function of not only weight but speed.
At 100,000rpm the shaft has massive rotational inertia.



The blow off valve does not remove any of the resistance on the compressor. It is still trying to compress with no power being applied.


Your incorrect there, the compressor cannot compress the air as it is free to escape through the bov. It is not really compressing air, it is pushing it through the bov.


The blow off valve is pretty much equivilent to opening the throttle but disconnecting the engine from the turbing housing. You're pumping air into something which is giving nothing back to you. It's going to slow down like a mofo.


Sort of. Its more like completly disconnecting the turbo from both the exhaust and intake at once. With the intake still conectected, the pressure is going to build up in the intake, with nowhere to escape. With a bov its got somwhere to escape, its not building pressure in the intake tract.






Of course air is flowing when the turbo is spinning. Moving air requires WORK. Under normal operation, that work is provided by input to the turbine. When you take away the input to the turbine where does the energy for the work on air come from? Kinetic energy of the rotating assembly.

Exactly


The more air you want to push off throttle, the faster your going to slow down the turbo shaft. It's fundamental physics; conservation of energy. You learn it in high school.

Believe me you learn about it much much more in depth studying mechanical engineering.

you should change your quote to
The more air you want to COMPRESS off throttle, the faster your going to slow down the turbo shaft.


The purpose of the bov is to stop the compressor from pumping air into a sealed compartment, where it will suddenly build high pressure, stalling the turbo from surge.

Pumping air into an inclosed compartment where it will compress and build pressure, takes more energy than the compressor pumping air through the open bov. Do you agree?

If so, than you will also agree that since the pump is working less, the shaft will decelerate at a slower rate?



The primary purpose of a BOV is to make the manufacturers a lot of money. If you have a link to evidence of BOV's doing any of the above to a tangible level please let me know. The majority of people who use them do so for the sound, or because they think that it will destroy their turbo otherwise. Not because they made a logical conclusion themselves, but because they were told so by other sheep.

Directly from wikipedia


Purpose of Relief and Blow Off Valves
Blowoff valves are used to prevent compressor surge. Compressor surge is a phenomenon that occurs when lifting off the throttle of a turbocharged car (with a non-existent or faulty bypass valve). When the throttle plate on a turbocharged engine running boost closes, high pressure in the intake system has nowhere to go. It is forced to travel back to the turbocharger in the form of a pressure wave. This results in the wheel rapidly decreasing speed and stalling. The driver will notice a fluttering air sound. In extreme cases the compressor wheel will stop completely or even go backwards. Compressor surge is very hard on the bearings in the turbocharger and can significantly decrease its lifespan. In addition, the now slower moving compressor wheel takes longer to spool (speed up) when throttle is applied. This is known as turbo lag.

With the implementation of either a bypass valve or a blowoff valve the pressurized air escapes, allowing the turbo to continue spinning. This allows the turbocharger to have less turbo lag when power is demanded next.

Ok now its your turn, find me some evidence to support the fact that shows that an un driven turbo will decelerate at the same rate, weather pumping air into a closed volume or pumping air that has somwhere to escape.:zip:

Great discussion guys!

[string]

Here's a quote I found on the internet: "Blow off valves are as useful at reducing bearing wear as a bunch of bananas in your intake". Relevence: as much as wikipedia.

I requested evidence, not a wikipedia quote; you should know the difference if you did indeed attend a university.

Obviously it's going to slow the deceleration of the shaft's rotation. But it's the same argument as the BOV and wear. You need to prove that it's reducing it by an ammount which serves a purpose. With or without a BOV you'll still have to recompress the charge pipes; the time to "re-spool" the extra lost rpm is what I am interested in, and arguing about.

If it only takes a fraction of a second to re-spool this ammount, then there is no real gain. You'll get a faster end time from taking your watch off before the race.

It's like selling a product for 1 cent cheaper than the competition. Who gives a **** about 1 cent. Who gives a **** about 10 miliseconds.

[Muzz]

I'd agree with the both of you if the compressor was actually a solid steel cylinder. Unfortunately, it isn't. Momentum is all well and good, until you realise you have a compressor trying to compress a full flow rate's worth of air without aid.

Now I won't bring any calculations into this, because we all know that no one likes those, but i'd hazzard a guess to say that the kinetic energy of a fully spooled turbo shaft, turbine and compressor, will be negligible compared to the energy requirement of half a second's worth of compression.

Good post, the truth is, the air pressure after u snap the throttle shut is going to build extremly quickly. The turbo is pumping a shit load of air, the throttle snaps shut, the pressure builds extremly rapidly till the shaft stalls. this will happen very very quickly.

With the bov, this massive instant build up of pressure dosnt happen, the air that is still pumping from the momemtum of the shaft can freely escape. its easier (less energy required) for the turbo to pump air into somthing that isnt already filled with high pressure air.




Now I won't bring any calculations into this, because we all know that no one likes those.

No, i do, i love calculations, thats why im studying mechanical engineering.
Please show me some calculations and ill verify what you are saying.
So, just wondering, what course are you doing that requires you to study fluid mechanics? Theres no way you could do any calculations without it!

[Muzz]

Here's a quote I found on the internet: "Blow off valves are as useful at reducing bearing wear as a bunch of bananas in your intake". Relevence: as much as wikipedia.

I requested evidence, not a wikipedia quote; you should know the difference if you did indeed attend a university.

What do you want proven? The fact that it takes more work to pump air into a high pressure zone than a low pressure zone? Thats what this is all about.

Can u prove that to pump an equal amount of air into a high pressure zore, and a low pressure zone takes the same amount of energy?

[string]

I've edited my post with far more relevant information to the argument.

I study Electrical Engineering. I don't have to study Mechanical Engineering to open a text book, we learn the same skills and you know it :)

[Muzz]

Obviously it's going to slow the deceleration of the shaft's rotation. But it's the same argument as the BOV and wear. You need to prove that it's reducing it by an ammount which serves a purpose. With or without a BOV you'll still have to recompress the charge pipes; the time to "re-spool" the extra lost rpm is what I am interested in, and arguing about.

If it only takes a fraction of a second to re-spool this ammount, then there is no real gain. You'll get a faster end time from taking your watch off before the race.

It's like selling a product for 1 cent cheaper than the competition. Who gives a **** about 1 cent. Who gives a **** about 10 miliseconds.

Have you been in a car with a blow off valve, once your on boost, you stay on boost through the shifts.
My mates car had the bov jam closed on him he didnt fix it for a while, while he was using the car with the jamed bov, it was a pig and had to build boost every gear change. there was lag in every gear. i have experianced this first hand. Same car without a bov, and with a good working bov after it was fixed. Im here lmao, that you think it dosnt benifit keeping spool up between shifts.

[Muzz]

I've edited my post with far more relevant information to the argument.

I study Electrical Engineering. I don't have to study Mechanical Engineering to open a text book, we learn the same skills and you know it :)

Yeah we do for the first year:thumbsup:
I didnt think electrical engineers study fluid mechanics though. Thats what this problem is mostly based upon.

A turbo, going from full flow capacity, to pumping that flow into a sealed compartment with say 15lts of volume, with nothing driving the shaft, is goin to stall very very quickly.

[string]

Yes.

With and without BOV, 2 litre, GT3040R and GT2871R. 1bar and 1.5bar respectively. No difference in either resulting in the car now running without. I can count the number of times I've shifted on boost, with a blow off valve, and seen the boost gauge stay above zero. None.

With a decent sized turbo, recompression of the charge pipes is where the time is going, not bringing the compressor just up to speed where it will actually generate positive pressure.

You are claiming that you keep boost between gears, yet your argument is based on the blow off valve removing all positive pressure in the charge pipes to remove the restriction? Make up your mind please.

How many years of your degree have you done? Starting second year this year?

As I said, you don't need to be enrolled in a course to be able to do it's content. All the engineerings are the same, they just find different things to apply the same forumlas too :D

[Muzz]

You are claiming that you keep boost between gears, yet your argument is based on the blow off valve removing all positive pressure in the charge pipes to remove the restriction? Make up your mind please.


No, what i am claiming is that the turbo dosnt loose spool anywhere near as quickly between gears with a bov. When you enter next gear, its going to reach full boost quicker if the turbo is at a higher spool rate.




With a decent sized turbo, recompression of the charge pipes is where the time is going, not bringing the compressor just up to speed where it will actually generate positive pressure.


lol, funny comment that. How can the compressor re-compress the charge pipes while the compressors not at a speed where it can produce positive pressure?:zip:

i thought it would be the other way around:
With a decent sized turbo, bringing the compressor just up to speed where it will actually generate positive pressure to begin re-compression of the charge pipes is where the time is going. :thumbsup:

Recompression of the charge pipes will happen much quicker after a gear change if the turbo is spooling at a higher rate!

Pressure is built up by the amount air being pumped.
The amount of air being pumped depends on how fast the turbo is spooling.

[civic_mods]

http://en.wikipedia.org/wiki/Blow_off_valve

[DLO01]

http://en.wikipedia.org/wiki/Blow_off_valve

See post No. 25

[string]

lol, funny comment that. How can the compressor re-compress the charge pipes while the compressors not at a speed where it can produce positive pressure?:zip:

It can't, i'm not saying that it can, i'm saying that time is a negligible quantity compared to re-compression time (as in re-compression after the shaft speed is back to the boost generation threshold). Pedanticism gets you nowhere. It pays to read too.


i thought it would be the other way around:
With a decent sized turbo, bringing the compressor just up to speed where it will actually generate positive pressure to begin re-compression of the charge pipes is where the time is going. :thumbsup:

Recompression of the charge pipes will happen much quicker after a gear change if the turbo is spooling at a higher rate!

Pressure is built up by the amount air being pumped.
The amount of air being pumped depends on how fast the turbo is spooling.
How much is "much" quicker. If it was so much quicker where are all the studies that BOV manufacturers are refering to to sell their products more?

You tell me that at high compressor rpm just after throttle release, it will keep spinning because of a lack of resistance on the compressor blades behalf. This is fair. You are not encountering any resistance to compression and are simply pushing air.

However, consider what happens when you jump back on throttle in the next gear. Let's say your BOV is very good at it's supposed job and it keeps the compressor at an rpm just where it would normally make boost when given some resistance, let's call this Rpm1. Now, without a BOV, the same turbo might fall to Rpm2. You are claiming that spooling from Rpm2 up to Rpm1 takes up "much" of the re-spool time. However, until it gets to Rpm1, you aren't building boost, you are just pushing air. As part of your previous argument, you are telling me that pushing air offers very little resistance. Infact, the engine probably helps the turbo spool a bit as it sucks air in, but that's a completely baseless argument of it's own.

If when no power is applied, this little resistance causes little rpm loss; isn't it logical to conclude that when full throttle is re-applied, the little resistance of the allows for a very quick gain of rpm? (up to Rpm1) With the newer ball bearing turbos this will be even more pronounced as there is very little resistance in all parts.

No one's butt dyno results are ever going to be conclusive; i'm always going to say that I felt nothing and you will always say you felt the opposite..

[Riviera]

i got one word - two/three what ever u want

wikipedia

lol

with the argument as is i think we can understand why and how but the question was when...

when u release the throttle

the pressure build up from the turbo is blocked off when the butterfly closes this causes the pressure build up to go backwards thats where the blow off valve comes in, it releases the pressure - built up air, realeasing it before coming back to the turbo...

call it a bypass valve if u will...

air travels down, butter fly closes, air needs an escape, vacuum to the blow off valve sense butterfly closed it gets the turbo pressure behind it, BOV opens releases the air....




here we go images from wiki-ma-pedia

http://i167.photobucket.com/albums/u148/Riviera001/Throttle_body_closedBOV7.jpg
http://i167.photobucket.com/albums/u148/Riviera001/Throttle_body_openBOV12.jpg

[Riviera]

also MUZZ is no the ball

the fluttering is not caused by back pressure its the type of blow off valve installed


edit - i am incorrect with this didnt research hard enough am doing so

[tRipitaka]

also MUZZ is no the ball

the fluttering is not caused by back pressure its the type of blow off valve installed

can't you get fluttering without a BOV at all..

[Riviera]

i highly doubt it i think it may be multiple BOV's(2), or its one with more tention in the spring

lemmie correct that ive just searched it up and found a forum sumwhere else


sequential BOV when it has 2 cylinders


still researching

[Riviera]

heres a qoute from another forum just google searched it and this is what the only person in there who thinks they know what theyre talking about, said...


gofastbits.com.au

The "Sequential" Myth
Added on 21st June, 2004

We’ve had a lot of enquiries recently beginning with the question “do you have the valve that makes that sequential noise?”. There is a common misconception that the fluttering, chirping kind of noise that people often hear, is caused by a sequential valve. This is NOT correct, in fact, there is no such thing as a blow-off valve that makes this kind of noise.

The term “sequential” is applied to HKS’ Super Sequential because it has two valves that open one after the other, the small inner valve opens first, which then pulls the second, larger valve open. By this definition, GFB’s Hybrid, Bovus Maximus and Stealth FX valves are also sequential, as there are two ports, which open one after the other.

The fluttering noise is in fact compressor surge, caused by pressurised air blowing back through the turbo when you close the throttle. Compressor surge occurs when the blades of the compressor “slip” in the air, much like an aeroplane wing stalling. This condition is most common when shutting the throttle and not opening a BOV far enough, but it can also occur with the throttle open under boost conditions if the turbo is not correctly matched to the engine. The fluttering noise is simply a result of the pressurised air trying to escape through the turbo, and the turbo attempting (under its own momentum) to cram it back in. The high velocities of the air involved can sometimes make a chirping noise in combination with the flutter.

Whilst the noise does not actually come from the blow-off valve itself, it can be caused by the blow-off valve. When the spring pre-load is set too hard, or the valve itself cannot flow enough air, compressor surge will result. Generally, if the spring is too hard, you will tend to hear the surge at low to medium RPM and boost conditions, with a normal “whoosh” at higher engine speeds and boost. If the valve is too small for the task, the surge will occur at high RPM and boost.

It is possible for the blow-off valve to open and still cause surge, as at lower RPM and boost the compressor is closer to the point of surging. Turbos can surge even with the valve half open at low RPM, and yet at high RPM even with the same valve opening, it does not surge. If you’ve ever watched the piston of a blow-off valve open when the turbo surges, you’ll usually see it flutter up and down, which is what leads people to think it is the valve causing the noise. It is in fact the pressure fluctuations in the turbo piping caused by the surge. If you hook a boost gauge near the turbo, you can see the pressure fluctuating as the compressor surges.

Ok, so how do I get that noise, then?
Quite simply, all you need to do is increase the backpressure in the turbo piping when you lift off the throttle. This can be done by removing the valve totally (not recommended – see paragraph below), or adjusting the spring on your valve harder. This will allow the valve to open at higher RPM and vent normally, and at low RPM will increase the amount of air flowing back through the turbo.

However, the noise that you get is totally dependant on your individual engine/turbo/intercooler/air filter setup. A stock intake air filter box will usually muffle the noise very significantly, pod-type filters will make the noise much more obvious. Secondly, the noise is very dependant on the type of turbo. Usually you will find that smaller turbos such as the TD04 used on WRX’s will not surge as readily, and do not sound the same at all. Nissan turbos such as those used on the 200SX and GTS-T readily surge at low RPM (accelerate moderately to about 3000 RPM, roll off the throttle, and you’ll usually hear it on a Nissan). Larger intercooler set-ups also increase the chance of surge, as there is a significantly larger volume for the valve to evacuate.

So if the noise is compressor surge, will it wreck the turbo?
This is a very grey area, dependant on too many variables to say yes or no. Generally, if the surge is only occurring at low RPM and boost, then there really isn’t going to be a detrimental effect on the turbo. You only need to compare the loads placed on the turbo at full boost near redline to the small amount of surge at low RPM to see this. If the surge is occurring when you are driving flat out at high boost (greater than stock), then the risk of turbo damage and/or a reduced turbo lifespan is greatly increased. Also bear in mind that driving style alone probably has the greatest effect on the life of your turbo!

[tRipitaka]

The fluttering noise is in fact compressor surge, caused by pressurised air blowing back through the turbo when you close the throttle.

so in fact, you don't need a BOV for flutter :)

[mrwillz]

its jus the turbo spinnin backwards isnt it? no BOV ftw
doseee it

[tRipitaka]

its jus the turbo spinnin backwards isnt it? no BOV ftw
doseee it

yep :thumbsup:

but dose is a different story.. you need a dose pipe for it :p

[Riviera]

duh read some more some things cancel the other out

heard performance right vehicles make the noise though wonder why they would do that to there turbos :( poor turbos

[string]

heard performance right vehicles make the noise though wonder why they would do that to there turbos :( poor turbos
Why don't you read your own quote where it mentions the damage, you seem to believe everything you read.

You'd have to really try to get a turbo to operate in the surge region under normal operation.

[Muzz]

It can't, i'm not saying that it can, i'm saying that time is a negligible quantity compared to re-compression time (as in re-compression after the shaft speed is back to the boost generation threshold). Pedanticism gets you nowhere. It pays to read too.

It does pay to read, this is what i read:thumbsup:



With a decent sized turbo, recompression of the charge pipes is where the time is going, not bringing the compressor just up to speed where it will actually generate positive pressure.


Time is a negligable quanity compared to re-compression time?
Sorry but thats really confusing, when you say time is negligiable, what time are you talking about?

All im saying is that re-compression time, time to full boost, whatever time your talking about, will be less if the spool is higher when coming on to full acceleration.


How much is "much" quicker. If it was so much quicker where are all the studies that BOV manufacturers are refering to to sell their products more?
I cant answer how much quicker. If letting of air pressure after the turbo when the butterflys closed is pointless, Why do manurfactures use recirculation valves?


You tell me that at high compressor rpm just after throttle release, it will keep spinning because of a lack of resistance on the compressor blades behalf. This is fair. You are not encountering any resistance to compression and are simply pushing air.

However, consider what happens when you jump back on throttle in the next gear. Let's say your BOV is very good at it's supposed job and it keeps the compressor at an rpm just where it would normally make boost when given some resistance, let's call this Rpm1. Now, without a BOV, the same turbo might fall to Rpm2. You are claiming that spooling from Rpm2 up to Rpm1 takes up "much" of the re-spool time. However, until it gets to Rpm1, you aren't building boost, you are just pushing air. As part of your previous argument, you are telling me that pushing air offers very little resistance. Infact, the engine probably helps the turbo spool a bit as it sucks air in, but that's a completely baseless argument of it's own.

Good argument there:thumbsup: However, i dont agree with this part:


You are claiming that spooling from Rpm2 up to Rpm1 takes up "much" of the re-spool time. However, until it gets to Rpm1, you aren't building boost, you are just pushing air.

I dont believe this is correct, the BOV closes as soon as you apply throttle again. You would most very likley be building boost well before you reach RPM1.


If when no power is applied, this little resistance causes little rpm loss; isn't it logical to conclude that when full throttle is re-applied, the little resistance of the allows for a very quick gain of rpm? (up to Rpm1)

Yes you are correct, remember though, the air it is pumping can no longer, escape through the BOV.

At low turbine shaft speeds, after a gear change, the engine might be injesting all of the air the turbo is pumping. The exhaust is driving the turbo hard and there is little resistance since there is not much pressure after the turbo, it will accelerate at a fast rate, as pressure builds, the rate of acceleration (of the shaft), lessens and lessens, as the resistance increases.




With the newer ball bearing turbos this will be even more pronounced as there is very little resistance in all parts

Fair enough, but hat about drag cars running a massive, laggy turbo. In this senario, you would much rather each new gear starts with the turbo spooling at 70,000rpm than 10,000rpm.



No one's butt dyno results are ever going to be conclusive; i'm always going to say that I felt nothing and you will always say you felt the opposite..

I am not basing this on my butt dyno. Im basing this on what my ears told me when riding in my mates s13 with the jammed BOV.

The turbo spool would sound like.
mmmmmmmmmmwwwwwwwwwwwaaaaaaaaaaaaaaaaaaahhhhhhhhh pissshhhh
mmmmmmmmmmwwwwwwwwwwwaaaaaaaaaaaaaaaaaaahhhhhhhhh
The exact way it does when accelerating from a stand still in first gear.

With the new BOV accelerating from 1st would sound like.
mmmmmmmmmmwwwwwwwwwwwaaaaaaaaaaaaaaaaaaahhhhhhhhh pissshhhh
waaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhh
the spool rate seemed to barly drop between gears!

Id guess that it was a minimum of 1 second longer (felt like 3 but ill play it safe;) ) it would take to reach full boost after each gear change, it wasnt a placebo, it was very very clear.

Obviously the effectivness of the operation depends greatly on the bov and the turbo system, so if you didnt notice any change, thats a disapointment.

Id rather my turbo enter each gear almost fully spooled, instead of barly any spool, as was the case of my mates car, which is quite laggy! try telling him BOVs do nothing!

[string]

Your mate's car had bigger problems than a broken BOV if you were getting 1 (or even more) second difference in spool between with and without the valve.

Also, get back to me when you've actually driven said car so you can control a few more unknown variables. For all you know your mate can't drive and without the BOV he let the engine rpm slip a little too low.

Manufacturers use recirculation valves for two reasons. Noise pollution, and emissions control when using MAF devices.



Yes you are correct, remember though, the air it is pumping can no longer, escape through the BOV.

At low turbine shaft speeds, after a gear change, the engine might be injesting all of the air the turbo is pumping. The exhaust is driving the turbo hard and there is little resistance since there is not much pressure after the turbo, it will accelerate at a fast rate, as pressure builds, the rate of acceleration (of the shaft), lessens and lessens, as the resistance increases.

You are missing what I am saying.

There will be a compressor shaft speed when to spin any faster, would result in compression, not just pushing air into the hungry engine. This is RPM1. There is little resistance up until this point simply because your pushing less air than is actually required by the engine (unless of course upon gear change we fall past boost threshold, in which case this argument is entirely pointless). Getting up to RPM1 will be incredibly fast because you now have a driving force turning the compressor just up to the speed where it would begin compression, no further.

If your mate's turbo takes "like 3" seconds (in an engine state where enough exhaust gas can be present to generate full boost, i.e. a reasonable rpm) to spin a turbo just up to a point where it will begin to compress, then he needs to stop using super-glue for oil.

I'm sure you're familiar with the TonyTheTiger's turbo GSR video? Sitting around about boost threshold from cruising throttle, it takes less than the time you are stating to hit rev-limiter let alone build up boost.