The BIG diverter valve / blow off / dump valve theory!

[truls000]

How it works:
When you take your foot off the gasspedal the throttle plate is shut/closed. The turbo is still spinning (as long as the engine is running) and blowing air through the IC and agains the closed throttlebody. All that boost/airpressure has nowhere to go, it's trapped between the throttle plate and the compressor. This is where the DV comes inhandy, the divert valve/dump valve opens up (when the pressure exceeds the set DV pressure) and eihter diverts the airpressure back into the TIP or dumps it info the atmosphere. If the DV has a to stong spring (airpressure relase set to high) or the DV dont work/open you will get whats called compressor surge (distressing sound). It can easily turn ugly, with shattered wheels or shaft bits all over the place. The dump valve prevents this condition, because as soon as the throttle is shut, it vents the excess pressure from the pipes, preventing this surge. This will reduce wear on the turbocharger and engine

Divert valve (DV) vs. dump valves (Blowoff) :
On engines with MAF (mass airflow sensor) its NOT recomended to use blowoff dump valves. When the blowoff valve dumps the compressed air into the free-atomsphere the MAF/ECU don't registed this (it still thinks the air is in the system). This results in a fuel-rich mixture after each valve actuation becuase the atmospherically vented air is not subtracted from the intake charge measurements. Therfore use divert valves!

Throttle response:
The MODIFIED dv placement (closest possible til the throttle boddy) is regarded best. The pressure build up starts at the throttle plate, this is where you want to divert/dump the 'over-pressure'. Therefore its most logical to place the DV on the cold side of your IC.

Stock:
As this illustration shows, the stock placement of the DV dumps hot air back into the turbo inlet pipe (TIP).



Modified
If the DV is re-located as this illustration shows, the DV dumps the cooled air back into the TIP.
Cooler air has a greater density. The greater the density of the charge mix in the cylinder the more power generated on combustion.



Blowoff Dump Valve:

[SEATONE]

Makes sense! Good info here thanks.

[rbj325]

I ran my DV on the cold side for awhile. There is no noticeable gain from doing it. If anything it was just more of a hassle to have to run the longer plumbing back to the TIP.

I also experienced a bucking issue while running my DV like that. Not sure if it was due to the DV though.

[hercfe]

OP,

Please refrain from doing anything that you might think is smart. This post is useless garbage. Not only do you have no idea of the principles of street-turbocharging, but you also have no clue about pneumatic theory.

[manhertm]

What about a hybrid valve?

[32_d3gr33s]

OP,

Please refrain from doing anything that you might think is smart. This post is useless garbage. Not only do you have no idea of the principles of street-turbocharging, but you also have no clue about pneumatic theory.

harsh...

[khj677turbo]

OP,

Please refrain from doing anything that you might think is smart. This post is useless garbage. Not only do you have no idea of the principles of street-turbocharging, but you also have no clue about pneumatic theory.

And todays asshole is...

[truls000]

OP,

Please refrain from doing anything that you might think is smart. This post is useless garbage. Not only do you have no idea of the principles of street-turbocharging, but you also have no clue about pneumatic theory.

Hi there 'hercfe'.

First off, this is a my theory (as written in the thread topic).
Ill take your criticism, but can critizie anyting whit out telling me whats wrong/to critizice?
Why is this/my post garbage?
Plese inform me about the 'principles of street-turbocharging' Ide love to learn :) ?

[dubgli]

haha. ouch! that is really harsh.. what is the true information about DV's and relocating the DV to the cold side if this thread is incorrect as it has been mentioned. Since this useless garbage is being posted here, someone might as well correct the information or knowledge and make it useful garbage from a learning/educational point of view..
any volunteers?

[truls000]

Throttle open, blowoff valve closed:


Throttle closed, blowoff valve open:


Note: Courtesy of Wikipedia.

[Saturnine]

Definition of a theory:

the·o·ry   
[thee-uh-ree, theer-ee] Show IPA
–noun, plural -ries.

1. a coherent group of general propositions used as principles of explanation for a class of phenomena: Einstein's theory of relativity.
2. a proposed explanation whose status is still conjectural, in contrast to well-established propositions that are regarded as reporting matters of actual fact.
3. Mathematics . a body of principles, theorems, or the like, belonging to one subject: number theory.
4. the branch of a science or art that deals with its principles or methods, as distinguished from its practice: music theory.
5. a particular conception or view of something to be done or of the method of doing it; a system of rules or principles.
6. contemplation or speculation.
7. guess or conjecture.

OP,

Please refrain from doing anything that you might think is smart. This post is useless garbage. Not only do you have no idea of the principles of street-turbocharging, but you also have no clue about pneumatic theory.

[PDX04a4]

OP,

Please refrain from doing anything that you might think is smart. This post is useless garbage. Not only do you have no idea of the principles of street-turbocharging, but you also have no clue about pneumatic theory.

you never cease to amaze me, by far the BIGGEST asshole on the forums. thanks for living up to your reputation once again.

[n7plus1]

the most efficient way the system works is how its already designed. the dv/bov should be as close to the turbo as possible for fastest operation.

[KMPRSSD]

the most efficient way the system works is how its already designed. the dv/bov should be as close to the turbo as possible for fastest operation.

Agreed. If the DV is located to far from the turbo then there is a posibility of more leaks. Couplings, FMIC, hose clamps, etc. I wouldn't take the chance of routing all that plumbing if it was possibly going to leak. I think the concept of sending cool air back to the TIP is a smart idea, but the way it was designed is best for proper response time.

[android3000]

It doesn't much matter if hot air is sent back to the tip anyway, it's going to pass through the intercooler again

[Ori0n]

I believe this would reduce performance for the reasons stated above. The DV should be as close to the turbo as possible so that the air that is being diverted, or not, has less distance/volume to travel/fill. I think if you ran it after the intercooler you'd just be slowing things down...

[spector]

I believe this would reduce performance for the reasons stated above. The DV should be as close to the turbo as possible so that the air that is being diverted, or not, has less distance/volume to travel/fill. I think if you ran it after the intercooler you'd just be slowing things down...

This. The air is still being cooled prior to going into the engine.

[nein-reis]

Why does this thread exist? I'm not trying to be an ass... but why are you making a theory about a subject that the answer already exists. Couldn't your time be better spent researching the answer then formulating your own guess?

[truls000]

Why does this thread exist? I'm not trying to be an ass... but why are you making a theory about a subject that the answer already exists. Couldn't your time be better spent researching the answer then formulating your own guess?

If so, please answer my question then; But is OEM or the MODIFIED dv placement best regaring throttle response?

[AudiA4_20T]

Negligible on the stock turbo

[drjonez]

...Throttle response:
But is OEM or the MODIFIED dv placement best regaring throttle response? Witch is the best solution regarding the amount of air needed to be compressed again? There is a lot of discussion on this subject all over the internett(fourms). Lets get the right answer once for all.

From a purely physics standpoint, you want to stop the pressure wave where it starts- at the throttle plate. This allows the compressor to continue spinning and keeps the piping/IC full.

The stock placement is simply done for packaging. Will you see gains by moving the DV? Probably not, given the tiny turbo. In a larger turbo system you would certainly see faster on-off-on throttle/boost response.

[nein-reis]

If so, please answer my question then; But is OEM or the MODIFIED dv placement best regaring throttle response?

Like these two already said... neither. Your throttle response will not change.

[diagnosticator]

From a purely physics standpoint, you want to stop the pressure wave where it starts- at the throttle plate. This allows the compressor to continue spinning and keeps the piping/IC full.

The stock placement is simply done for packaging. Will you see gains by moving the DV? Probably not, given the tiny turbo. In a larger turbo system you would certainly see faster on-off-on throttle/boost response.

I agree.

Since the throttle plate is the point of blocking the charge air flow from the turbo/intercooler, the DV placed nearest the throttle body to recirculate the air flow at the point of blockage, is the technically better setup. When the DV recirculation air flow path exists just before the throttle, the air flow from the turbo will not change during brief throttle closures, because the pressure wave reflection from the closed throttle plate does not develop and travel back to the turbo. Regardless of if the effects are noticeable or otherwise worthwhile to implement or not, the DV placed close to the throttle body will result in the maintainence of pre shift turbo RPM and air mass flow rate during throttle closure transients better than the stock DV location. Intuitively, I believe the relative increased throttle responsiveness with the DV placed close to the throttle body is about the same amount of throttle response improvement typically noticed with the DV installed in the reverse from OE orientation. Without detailed measurements and tests, the results is only a subjective variable, more or less for each driver.

[widgget]

diagnosticator was here.

/endthread

[audi1.8tFTW]

Well i read the entire thread and found that the better way to do it would be that :

[android3000]

Diagnosticator confirmed that closest to the throttle body was best, did you miss that?

[dubgli]

nvm.. i didn't even look at the arrows.

[nein-reis]

Coming from the IC????

[Casius]

I agree.

Since the throttle plate is the point of blocking the charge air flow from the turbo/intercooler, the DV placed nearest the throttle body to recirculate the air flow at the point of blockage, is the technically better setup. When the DV recirculation air flow path exists just before the throttle, the air flow from the turbo will not change during brief throttle closures, because the pressure wave reflection from the closed throttle plate does not develop and travel back to the turbo. Regardless of if the effects are noticeable or otherwise worthwhile to implement or not, the DV placed close to the throttle body will result in the maintainence of pre shift turbo RPM and air mass flow rate during throttle closure transients better than the stock DV location. Intuitively, I believe the relative increased throttle responsiveness with the DV placed close to the throttle body is about the same amount of throttle response improvement typically noticed with the DV installed in the reverse from OE orientation. Without detailed measurements and tests, the results is only a subjective variable, more or less for each driver.

Makes sense to me

[pape]

I dont see anything wrong with this question that was posted by truls000, In fact am happy he even asked it. As I say the only stupid question it the one you dont ask.

Proof that this is a good post...... (many of you did not know that the BEST place to mount a BOV is as close as posible to the throtle body, well now you know.) and Diagnosticator explained why.

[a4darkness]

Ignoring the DV placement debate as this one's pretty much been put to rest. However it's discussion threads like this one that usually inadvertently teach ppl things. So at least in that regard, it's good to bring ideas like this up.

The notion of sending cold air back into the DV is an interesting one, albeit not really feasible. I was just thinking about it and this comical notion popped into my head... using the OEM SMIC to cool the charged air awaiting re-entry into the turbo, but positioning it on the pass side where the DV currently lives. But then again, that's under the turbo... prob not the best place for an IC. ha ha ha

EDIT: just realized the DSMIC is under the turbo... duh

[truls000]

OP,

Please refrain from doing anything that you might think is smart. This post is useless garbage. Not only do you have no idea of the principles of street-turbocharging, but you also have no clue about pneumatic theory.

the most efficient way the system works is how its already designed. the dv/bov should be as close to the turbo as possible for fastest operation.

Agreed. If the DV is located to far from the turbo then there is a posibility of more leaks. Couplings, FMIC, hose clamps, etc. I wouldn't take the chance of routing all that plumbing if it was possibly going to leak. I think the concept of sending cool air back to the TIP is a smart idea, but the way it was designed is best for proper response time.

I believe this would reduce performance for the reasons stated above. The DV should be as close to the turbo as possible so that the air that is being diverted, or not, has less distance/volume to travel/fill. I think if you ran it after the intercooler you'd just be slowing things down...

By the looks of it, you were all wrong !

[truls000]

drjonez

diagnosticator

Thanks to you both for the informative and logical answers!

[Bische]

One thing not mentioned is when hot compressed air is released it cools down rapidly, at high pressures with a BOV you can even see the condensed water blowing out.

[audi1.8tFTW]

haha i was just kidding with the ic thing .. hahaha

[M-Hood]

When you take your foot off the gasspedal the throttle plate is SHUT, but all that boost has nowhere to go. It's trapped between the throttle plate and the compressor, that still spins for a fraction of a second, as inertia and a few remaining exhaust gases still try to spin the turbine. That is a wall of pressurised air that won't let the compressor turn as fast as it needs to - but the turbine doesn't know that yet (it will, in a while, because no combustion creates no more exhaust gases, but it takes some time to respond). So the turbine tries to spin the shaft, but the trapped boost forces the compressor to stop spinning.

Just about everything you said there is wrong. You might want to pick up a book on turbo charging.

First off, the turbo never stops spinning till you turn the engine off. On ball bearing turbos it can keep spinning for more then 30 seconds without anything blowing thru the exhaust housing. That is well beyond a fraction of a second.

Also you might want to pick up a book on how a engine works. If the crank is spinning it is producing exhaust gas or air, even if your not spraying fuel into the cylinders the engine is still producing vacuum sucking in air and that air has to be pushed out the exhaust valves and thru the turbo. This is still going to spin the turbo, it isn't like the WG open at that time.

Not sure why some people think the turbo stops spinning just because they got off the throttle.

[truls000]

Just about everything you said there is wrong. You might want to pick up a book on turbo charging.

First off, the turbo never stops spinning till you turn the engine off. On ball bearing turbos it can keep spinning for more then 30 seconds without anything blowing thru the exhaust housing. That is well beyond a fraction of a second.

Also you might want to pick up a book on how a engine works. If the crank is spinning it is producing exhaust gas or air, even if your not spraying fuel into the cylinders the engine is still producing vacuum sucking in air and that air has to be pushed out the exhaust valves and thru the turbo. This is still going to spin the turbo, it isn't like the WG open at that time.

Not sure why some people think the turbo stops spinning just because they got off the throttle.

Thanks for the informative answer... I updated the #1 post :)