FLUTTER sound as BOV

[chrissso]

You're going to have to unpack that for me, and explain how air flowing in a different way can also be applying force in the same direction as when its not flowing in this "different" way.

<{POST_SNAPBACK}>

Well... The turbo is still spinning in the same direction. And so the force would still be on the same side of the turbo blades - the leading edge. Here's why. Surge is just air escaping back through the blades because the pressure inside the plumbing is bigger than the air pressure being pumped in. You get flutter because the turbo is still spinning after a surge and now that the presure is lower inside, the turbo draws more air in again. Then it surges again etc, etc. So multiple surges gives you the flutter.

So, If the force was on the other side of the blades, the turbo would spin backwards and you would not get the repeated surges.

I agree with what someone else said on this thread that backward spinning turbos is a myth. They spin at 100,000 rpm, you can t easily stop that, lots of inertia built up there. You would need really friggin high boost and high boost means a turbo spinning at 200,000 rpm - Even harder to stop.

[scathing]

Before I continue with this discussion, would you agree that a turbo setup with no BOV spools down faster than one with a BOV?

Having never driven a car without a BOV I can't say from personal experience.

[[HOTNXR]]

ATTENTION:

Now from what ive been reading, my opinion is a BOV is not needed.

But can someone back me up by saying the PSI we are talking is the same PSI you pump a tyre up? also id like to say 10psi is something you can hold the pressure with your thumb... is this correct? so even 20 is pretty weak. your tyres are 34psi...

also if the blades went backwards, wouldnt that cause the exhaust wheel blades to go backwards to, causing exhaust to go BACK into the motor??

[paulr33]

Well....

The air in the plumbing has to go somewhere right?

It goes back out of the turbo (surge) and into the atmosphere, passing the airflow meter on the way which read some airflow and the ecu pumps fuel through your injectors giving you a black puff of smoke.

If you have an atmo BOV, the turbo keeps sucking air and the air flow meter reads the air - etc.. see above for the rest.

A plumback keeps the air circulating through the plumbing,after the airflowmeter, the aflowmeter doesn't register any airflow and there is no polution.

<{POST_SNAPBACK}>

The standard BOV recirculates back into the front of the turbocharger to be re-used again. The standard unit is *not* an atmo BOV. So again:

How does fitting a BOV correct emissions? The standard skyline bov's simply recircluate back into the intake system. Without a bov the air is still in the same location. I don't see how it "helps emissions". The BOV is simply there to prevent compressor surge when the throttle body is closed

[Freeman]

I bought my skyline two days ago and it does this massive flutter every gearchange higher than 2000 rpm. the front mount pipework was custom made and where the stock blowoff valve usually is there is just a pipe running to a hole in the side of the plenum at the back. Anyone know whats going on?

[chrissso]

The standard BOV recirculates back into the front of the turbocharger to be re-used again. The standard unit is *not* an atmo BOV. So again:

How does fitting a BOV correct emissions?  The standard skyline bov's simply recircluate back into the intake system. Without a bov the air is still in the same location.  I don't see how it "helps emissions".  The BOV is simply there to prevent compressor surge when the throttle body is closed

<{POST_SNAPBACK}>

To clear up. Bov's in general remove surge.

Plumback bov's are more emmision friendly.

So, nissan fit plumbacks instead of atmo.

yawn.

[chrissso]

I bought my skyline two days ago and it does this massive flutter every gearchange higher than 2000 rpm. the front mount pipework was custom made and where the stock blowoff valve usually is there is just a pipe running to a hole in the side of the plenum at the back. Anyone know whats going on?

<{POST_SNAPBACK}>

Hey I think that might be your vacuum line to the breaks??

Sounds like you just have no bov!?!?

Got any pics? This would help.

[chrissso]

Before I continue with this discussion, would you agree that a turbo setup with no BOV spools down faster than one with a BOV?

Having never driven a car without a BOV I can't say from personal experience.

<{POST_SNAPBACK}>

I have an ajustable spring rate bov and I'll do some experiments with it. At either extreme it will give you lots either of flutter or lot of phish. Then i'll post the results. I have played around with the adjustment before though and I didn't notice any difference in immediate power after gear change. However , I wasn't looking for it. Its interesting to hear what alot of other people say in other threads about the improvement in performance that stock BOV gives them vs atmo bov... Alot put it down to the adjustment of the atmo bov. My car never came with the stock bov so I don't know.

[paulr33]

To clear up.  Bov's in general remove surge.

Plumback bov's are more emmision friendly.

So, nissan fit plumbacks instead of atmo.

yawn.

<{POST_SNAPBACK}>

Ok so we agree that BOV's remove surge or prevent it. But 2 pages ago we have lots of people stating the BOV's are pointless and they do nothing. Nissan began fitting BOV's to factory cars as this decreased the rate or frequency of turbo failure (I believe).

So do we all still think they are useless?

[chrissso]

Ok so we agree that BOV's remove surge or prevent it. But 2 pages ago we have lots of people stating the BOV's are pointless and they do nothing. Nissan began fitting BOV's to factory cars as this decreased the rate or frequency of turbo failure (I believe).

So do we all still think they are useless?

<{POST_SNAPBACK}>

Car manufacturers try to get there cars as quite as possible so nissan fit a bov to prevent surge noises, and plumb it back to eliminate atmo presure release noises and help with emmisions. If it does infact prolong turbo life, then I guess its an added bonus. But at an expected factory boost of 5-7 psi - it ain't gunna do shit to the turbo if you remove the BOV.

[paulr33]

There were no concers over emissions for non BOV'd nissan engines. Look at the rb30et it was supplied to holden as an OEM engine by nissan without a BOV. BOV (assuming OEM is recirculate, as all are) or no BOV the emissions are the same.

The air is still in the inlet system (before exhaust / cat). With a BOV it is plumbed to be reused correctly. WIthout a BOV it is not replumbed and causes surge but it is still reused. Neither will vent to atmosphere so they dont affect emissions.

Noises is certainly a possibility as far as emissions go but certainly i dont believe the driving force behind fitting factory BOVs. The VL's passed all the ADR rules and emissions stuff when they were in production run in 1986. I still believe BOV's were fitted as standard parts to prevent turbocharger failure and increase turbocharger life span

[chrissso]

The emmission regulations were changed not long after 86 and car maunfacturers were always ahead of the regs by a few years. That would support agument for fitting bovs for emmision control. Otherwise, why don't VL's have bovs if they prolong turbo life? Have you noticed that fewer turbo cars are coming out of Japan recently due to even stricter emmision laws changing again?

Don't forget that in a non bov'd car that the compressed air still has to go some where. Some of it would go through the idle jets (old carby speak) or whatever it's called. The rest has to surge out in bits through the turbo. This released air still has to go through the MAF in reverse. You might even get an occilation of air in the MAF from the surge. this air will still register and the ECU will still calculate an amount of fuel to squirt into the engine. And this will just vapourises into smoke as there is very little air actually going through the engine to burn it up.

[paulr33]

ok does anyone else here think a bov is a pointless item on a car and we should all just block them off and run it flutter mode?

[Tigger]

I took a picture of what I think is the stock BOV.

What do i do with the pipes to make the flutter sound occur? Which pipes to i need to block or reroute??

[Rolls]

I took a picture of what I think is the stock BOV.

What do i do with the pipes to make the flutter sound occur? Which pipes to i need to block or reroute??

<{POST_SNAPBACK}>

Yes that is the stock bov, the smaller tube is a line for vacuum so that it knows when to open, the bigger one is where it vents the air. Blocking off the 2nd one so it doesnt have anywhere to go would probably do it. However blocking off the smaller one may make it never open or stay open always, not all that sure.

The other tube I have no idea but my redtop rb20 had one as well. Probably a vacuum control for something.

Edited November 14, 2005 by Rolls

[Freeman]

Hey mine makes the flutter noise and i took some pics but i cant post them. does someone want me to email them to them so they can put them up?

Looking at Tiggers picture, mine is the same exept there is no blowoff valve and instead a pipe running from the intercooler piping straight out about 10cm then turns left and appears to plug into or run under the back of the plunum, very close to the blue plug you can see in his pic.

[Jago]

ok does anyone else here think a bov is a pointless item on a car and we should all just block them off and run it flutter mode?

<{POST_SNAPBACK}>

nope, i think they help a bit

[krzysiu]

I blocked up the stock bov and the car runs like crap. You can really feel the turbo slowing down during shifts. You also notice heaps of backfire. After 1 drive i unblocked the bov and the car ran normal again. It wont hurt your tubo, but your car will run like crap.

[paulr33]

i dont see how more obvious it could be? the BOV or reciruclation valve is purely designed to extend turbocharger life vs a NON BOV setup

[scathing]

I blocked up the stock bov and the car runs like crap. You can really feel the turbo slowing down during shifts.

Still waiting on chrissso to get back to me on his experiences. But what you're saying is what I've also heard about non-BOV cars.

Before people reply back saying that the big, f**k-off, drag cars don't run BOVs...they're also set up a lot differently to a street car, and since their gear changes tend to be flat throttle and a lot quicker, they don't have to worry about it as much.

My understanding is that the OEMs started putting BOVs (as opposed to no BOV) to reduce turbo lag, which is what you experienced.

They chose recirculating valves as opposed to venting ones because of the emissions due to AFM setup and noise issues.