Clashez

iTrader: (5)

This is the question a circulation bypass valve (CBV). It essentially serves the same function as a BOV but does it by venting the excess pressure back into the intake system so there's no loss of metered air as oppose to a BOV venting the excess pressured air into the atmosphere. So wouldn't that make it better then a BOV (Blow off valve) the CBV also doesn't make the pssst sound so it would also be helpful if you or I would want to go the stealther way of Turboing .

Just weighting out different options any useful info would be great

5th gen dd

There is no performance gain to be had from it venting back into the intake. This is done by manufacturers to prevent the possibility of contaminants making it's way into the engine if boost was vented into the atmosphere. Since you are off the throttle at the time that the excess air is being released it will not benefit the turbo and any beneficial amount of pressure built within the intake pre-turbo will release via the air filter since it is the path of least resistance.

On cars that measure air volume via a AFM sensor and have a turbo from the factory, you will have a poor running condition when venting to atmosphere due to the ECU anticipating the surge of air in the intake. The surge is minimal but enough to effect how the car runs. Where as engines that read air density via a MAP sensor are not effected by this because it is metering off the pressure reading in the intake manifold itself. An example of the this is the 2nd gen 3sgte (89-94 MR2, Celicas, etc.) uses a MAF sensor so if you vent to atmosphere the car will run like crap but the 3rd gen 3sgte (94-99 JDM onry yo), which relies solely on it's MAP reading can be safely vented to air. I have the latter of the two in my MR2 and use an Apexi BOV. Even vented back into the intake the stock CBV (BPV in toyota world) still have a bit of a woosh when letting off the throttle but it's certainly nothing compared to a ricey SSQV.

There is a possibility of a performance gain and a better ability to maintain boost if you run no BOV at all. Many people will cry compressor surge at the mere mention of this, but with a precise tune this setup can and has worked, grand touring cars do this all the time. The only time you are at risk of compressor surge is if there is some sort of major misfire due to poor tuning or component failure.

TunerMaxima3000

iTrader: (4)

Oddly, I'm going to help you. I want you to realize that I'm doing this because you sincerely put together a good question with good grammar, and have shown that you've done some measure of research here.

This is information as I know it for TURBO (SC is different, don't confuse them). First, Turbos don't traditionally run any circulation style Wastegates, that is for Superchargers primarily. What you're talking about in a Turbo is normally a "Wastegate".

BOV (Blow off Valve) - Once a certain pressure is reached in the Intake charge pipe (as close to the Turbo as possible) that pressure overcomes spring pressure in the BOV, and the BOV opens.
When it opens pressurized air is purged out into the atmosphere. This happens until the pressure in the Intake Charge Pipe lowers below the spring opening pressure of the BOV.

Wastegate - These are normally part of the Turbine housing (exhaust side of the turbocharger). Sometimes they're external actuators. In that case, A little air line runs from the Intake charge pipe over to a little pot-looking unit with a rod on it. This little pot unit has a spring in it jsut like the BOV. Once the air overcomes the spring pressure the rod moves, this opens the valve inside the Turbocharger Turbine housing.

When that Valve in the Turbine housing opens, exhaust bypasses the Turbine wheel, so essentially, the more that wastegate valve is open, the less the turbo spins, which equals Less Boost.

Wastegate setups do not modify or change the INTAKE air flow, the change the EXHAUST air flow.

BOV's just dump off Intake air flow.






Now... the circulation thing is mainly for superchargers, which are run by a pulley that you can't really disconnect easily when you want to change boost. This I'm not as familiar with, but if you're turbochargning it should not apply to you anyways.

I could have some of this wrong, but that's my understanding of the applicable turbo systems.

First paragraph is a lot of misinformation and presumption, unfortunately.

Second paragraph is a lot of truth, but only if the BOV is installed AFTER the metered air. This is the incorrect way to set up a turbo anyways with MAFS system, though most guys do it this way that don't know better. The MAFS is supposed to see the air the engien is getting regardless of the setup, if it's pre-charge metering that is NOT accurate measurement regardless of the BOV setup.

5th gen dd

Tuner's description is correct. Additionally, recirculating a wastegate on a turbo will just cause overboost. The purpose of the wastegate is to maintain a desired pressure. Once the desired pressure is reached the wastegate will open (this was all explained in Tuner's post) to maintain this pressure. If you somehow recirculated the exhaust gases released by the wastegate back into the turbine, you're going to end up with a $1500+ paperweight. This is why on big HP setups most downpipes have a dedicated "screamer pipe" which is basically an open dump pipe for the wastegate. Once you're at that level though there's nothing sleeper about it.

TunerMaxima3000

iTrader: (4)

As much as I hate to disagree with you when you're agreeing with me, I hate misinformation more so I just feel the need to clarify.

A wastegate is a little valve inside the turbine half of the turbo (exhaust).

Normally the Exhaust goes into the exhaust manifold and then into a single collector, then into the Turbo's Turbine housing and that exhaust gas passes over/through a Turbine wheel. It spins around and then through the turbine wheel and is forced out the center of this wheel and out the Normal exhaust pipe (down-pipe).

When the wastegate is opened, all that happens is some of the exhaust gas is redirected, instead of all of it going to the Turbine wheel, some of it goes directly past the Turbine wheel through the Wastegate port and out into the downpipe.
The exhaust literally bypasses the turbine wheel and goes into the downpipe. There is no 're-circulation' with a wastegate.

It's either:
Closed(exhaust goes to the turbine wheel and spins it)
or
opened (some exhaust bypasses the wheel through the opened wastegate due to 'path of least resistance', the amount of exhaust that bypasses is directly related to how much the wastegate is opened)


After writing all that, I realize that this is confusing to say the least. I couldn't find a good GIF of it but this shows pretty good a normal wastegate.

What you're looking at is the Turbine (exhaust side) housing with the Down-pipe (exhaust pipe) removed



The Turbine wheel should be obvious. So should the steel flange that mounts to the exhaust manifold.
Now picture the flow, exhaust gas enters, is forced around the Housing ("snail" housing) which spins the turbine wheel and then the gas comes out the center of that wheel and out the exhaust.

Now, do you see that little round piece that is to the left of the compressor wheel? that's the Wastegate valve. It opens up and the exhaust passes right by the turbine wheel.

5th gen dd

Agreed, my post was a bit off. Was just waking up. The CT20b on my car has an internal wastegate as well. It looks very similar to the picture you posted only the wastegate valve is a bit bigger. The wastegate works with the boost controller to control how much the turbine spins by opening the wastegate butterfly to bypass the turbine itself thus controlling how much it spins and pushes boost into the motor. My experience with turbos is strictly with the 3sgte in the MR2 so my knowledge with FI on this platform is limited and designs will definitely vary between vehicles. The AFM is the main bottleneck in 2nd gen 3s because it is a trap door design.

My comment about recirculating the wastegate should've read not only is this detrimental to control of the turbo, it's pointless and not really possible. But I think he is just wanting to know what to do with the vroompssh noise anyways.

5th gen dd

Somewhat unrelated page but the first half has some useful information.

http://people.physics.anu.edu.au/~amh110/blow_off_valve.htm

Clashez

iTrader: (5)

So there really is no real performance gain or loss going with a BOV or CBV style , other then the fact the bov release's pressure into the atmosphere and makes the pssst sound. Only reason I was thinking of going with CBV is I have a few friends running them on there Turbo volvo's and you couldn't even tell they were turbo'ed unless you know cars or they popped there hood . The sound is very milded and was thinking it would be a great way to be super stealthily and still be safe ( not using a bov at all)

* wow simple question became a very informative thread
Thanks guys

TunerMaxima3000

iTrader: (4)

You asked for the difference. lol. Not a very specific question.
If the Turbo doesn't have a wastegate and you need a BOV:

Atmosphere vent: Loud noise during purge. If the MAFS sensor is positioned incorrectly for boost application you will have fuel management issues with this setup.

Recirculate vent: No noise during purge. If MAFS sensor is positioned in the wrong position you will have LESS fuel management issues. This isn't ideal because you're putting positive (boost) pressure into low-pressure areas of the intake, these areas can't hold the boost, it will leak off. BUT the MAFS will see an increase in pressure still and still won't get all that air it thinks it's going to get.

The short of it: You can do either, Atmosphere vent is better if you NEED to use a BOV (no wastegate).

there is one more option that applies to guys that need a BOV, have proper MAFS setup, and don't want the noise, a surge tank. This basically is just a holding tank for the boost to purge into so it doesn't make a big obnoixious noise when purging. If you want proper MAFS setup and no noise, this is what I'd recommend.

Clashez

iTrader: (5)

Tunermaxima3000 and 5th gen dd thanks for your help it was very much appreciated

Quickywd01

iTrader: (16)

For the centrifugal supercharger you'd want a valve that can open partially during idle or when off-throttle cruising so that the air can escape. On 4th gen's you don't have to worry about metered air escaping.

TunerMaxima3000

iTrader: (4)

Huh? He asked about turbo, and there's no reason to have boost bleed off at idle....

Centrifugal SC's make boost proportionate to RPM, at idle the car will still be pulling a vacuum, not boosting.

T_Behr904

Externally wastegated turbo's are better imo...

TunerMaxima3000

iTrader: (4)

Nicer if you want to change boost.

T_Behr904

I'm serious. Externally wastegated turbo systems on older Audi's and Porsche's are bulletproof. Easy to get more boost from them, too. Besides a stiffer wastegate spring, you can also shim it. Turn a screw on the CIS injection pump to add more fuel and you're good to go. External wastegates are commonly used for regulating boost levels more precisely than internal wastegates in high power applications as well. You'll see external wastegates on "serious" higher power builds.

The Wizard

iTrader: (43)

Huh? There is no boost at idle... regardless if SC or turbo


OP,
FWIW, a BOV in a sense is a CBV as you call it, just w/o the recirculation hose.

Redline Maxima

iTrader: (10)

I have a question in regards to a particular BOV. How come no one has ever used a GReddy Type R BOV for their boosted application? Is it the price or it just doesn't work or isn't right for setups on Maxima's?

Clashez

iTrader: (5)

The GReddy Type R BOV is one that i had in mind

EvoTillIDie

iTrader: (1)

Funny how I just saw this a while ago, hopefully it helps here

TunerMaxima3000

iTrader: (4)

Not what I meant when I said that, but he was right either way, my understanding of Centrifugal BPV's was precisely '0' at that time. Totally different setup


agree