hehehehe

[hehehehe]

hi guys

this may sound like a really stupid question to alot of you here but my mate was playing round with my BOV on r33 and disconnected the little hose from the top of the BOV and blocked it with his finger and revved the car and it made a mad fluttering noise compared to the standard psshhhh noise.

He said to me i can keep it like that just remove my stock BOV and seal its area with a metal flange and all piping around it and i wil get a very distict loud noise as i have a fmic.

NOW i am wondering is it safe to remove the stock BOV or will this damge anything. i am running 5 pounds ( i know pretty low but my solenoid is screwed or something).

So please i need answer ASAP whether it is safe.

thank you

[Al]

What a friend, they have just shown you how to f**k up ya turbo. Excuse the sarcasim, but people who don't know much about turbo's and start playin around with other people's cars really annoy me.

The "flutter" noise you hear is the air bouncing off the throttle body (as it shuts) then re-entering the turbo, in the opposite direction. This will gradually damage any turbo, but with the r33's the exhaust turbine is ceramic, so it will blow it much faster.

[hehehehe]

sorry to continue my stupidity but the noise came from my apexi pod as i have heard the same noise on my cousins 180 when i put my pod on his car

please explain

[hehehehe]

also when he did this on my car we went for a drive only below 3000 rpm it made that noise but high revs it made the standard psshhht scream

[Al]

The bov is designed to expell the compressed air when the throttle is closed, by doing this it keeps the turbo spinning between shifts. Now, if the hole is blocked the air can only force it's way through the turbo (in the opposite direction) and out the air pod.

Also, this is done while the exhaust turbine is trying to spin the turbo in it's proper direction. So you have air passing in opposite directions, trying to spin the turbines in opposite directions, so eventually you will get excessive wary leading to a blown turbo.

The way i look at things: All parts cost money, if nissan did not feel it neccessary to fit a bov they wouldn't. Whether the bov is plumbed back to the intake, or expelled into the atmosphere is irrelavant, the later only being an illegal EPA issue.

Hope this helps

[JimX]

Originally posted by hehehehe

sorry to continue my stupidity but the noise came from my apexi pod as i have heard the same noise on my cousins 180 when i put my pod on his car

please explain

Compressed air bounces off closed throttle body. Usually it vents back through the BOV and into the intake again, but if you block it off it goes back through the turbo and gets chopped up by the turbo. You then hear it out your pod.

So it's kind of like this: Air bouncing off the TB gives the noise its "power source", the turbo impeller blades chop up the air and create the noise, and you hear it out your pod/air box because that's where the air escapes.

If it makes the normal bov noise at high revs chances are he hasn't sealed it properly and the higher amount of compressed air is able to force its way out the bov.

[darkstar]

Al, i am that friend who was mucking around with the vacume signal to the bov. For your information, i now a lot abot turbos and associated performance increases, not to mention built engines as well as performance packages with good results.

I was interested to see how it sounded at low boost (about 1psi when free reving the engine a little). heheheh (mena) decided that thats what sound he wanted and i told him that running the hose off the bov and blocking it, youll get the chop-chop noise on low boost due to the bov not opening, but at high boost, you will get the bov to open as it can sense the pressure through the intercooler pipe to open, combined with the nipple on bov being to the atmosphere, the bov will open.

The noise everyone refering to is indeed compressor stall. Similar kind of noise that you get when you have a turbo clearly too big for the motor, thus forcing in more air that the motor can consume even at WOT.

I told mena that this will not be the best thing to do performance wise, as during gear changes or throttle off he will get backfiring due to running rich, because the AFM will register air going into the turbo and also out of the turbo due to the compressor stall.

Such enrichment from an emissions prospective is undesirable, can can cause the car to fail emissions testing. Hence a bov is fitted MAINLY for emissions reasons, not to prolong the life of the turbo per se. Prolonging the life of the turbo might be an arguable side advantage, but its not a primary concern for nissan if they cant pass emission laws.

Consider your turbocharger system for this explanation. The turbo is working and rotating in a clockwise direction, generating boost that goes to your intercooler. Since the air is providing resistance to the shaft and compressor wheel, the shaft will have more loading on one side than on the other, because it moves in a a clockwise direction. When the air comes back after throttle closure, its only for a breif moment (2-3 seconds) that the shaft is slightly loaded in the opposite direction to normal operation. Therefore the ware characteristics from compressor stall would be null, as the wear is already biased due to the normal operating of the turbo.

Ive quoted Nizpro's Simon Gishus from an article which will help clear things up more.

"Some people do think that at the absolute upper extremes of boost levels - about 30-plus pounds - the blow-off valve does, somewhat, save the compressor wheel and shaft from trying to rotate backwards. It doesn't actually rotate backwards at all - all you're hearing is cavitation. What happens is, you've shut the throttle, the turbocharger is doing 100,000 rpm and now has a boost spike of 50 psi. Because it's working in a higher region than what it's designed for, it slips; it basically does a skid like a car tyre does when you dump the clutch. That's the noise you hear - the whoof-whoof-whoof is the air doing a skid."

Simon has also spoken about how having a BOV (plumb back or externally venting) can decrease lap times. He noted a 2 second quicker time by using no BOV around Winton race track. The theory is that when the bov opens, it releases the air in the pipes closest to the throttle body. As such the air has to be replaced again, by the turbo when the accelerator is pressed, such a replacement could the factor that decreases the lap times. Also with no bov, you can boost spike during fast gear changes by around 0.5-2 psi, which can make the car all that quicker while setting up for cornering. Most cars in WRC dont run a bov for this reason, as they lift on and off the throttle numerous times to control the boost pressure and response of the car in some stages.

"The fact that people think that [The BOVs] keep the turbo spinning [due to no compressor stall] is a problem. The people that suggest this have never had an engine on the dyno and never had a turbo tacho in their hands. What people don't realise is, when you shut off the throttle, you shut off the air supply to the engine - this shuts off the exhaust gasses coming out of the engine. When there is no exhaust flow, there is no energy to keep the turbine spinning - the turbo slows down at an alarming rate."

I hope this clears up some misconceptions about turbos and bovs together.

Bovs have their place both on the street (emissions and also keeping the car a sleeper if its Plumbed back) and on the track (when running high ( 30psi +) boost pressure ). Wank factor externally venting valves have no placement for any performance gain, but a plumbed back can certainly add benefits when done correctly.

[Al]

darkstar:

I really appreciate you info.

From Hehehe's first post, i got the impression that this was done by a friend "backyard style". It is obvious, that you know more than i, about this matter and appoligise if i offended you.

Having said this thou, i still beleive it is a bad idea to block the bov in a R33 due to the increased load on the "ceramic" exhaust wheel.

I have known that race cars do not use bov, and the reasons/advantages behind it. But, race cars have the financial advantages of getting things replaced when needed. I beleive that for street use, on a non-to-lightly modified car, the gains are not benifical, especially when weighing it up against the increased risk of spinning off the "ceramic" turbine wheel from it's shaft.

If Nissan found it benifical and cheaper to have no bov, the tunning of the ecu may have overcome the epa issue.

In Ending: We all learn from different sources, experiences and interpritations. At the end one must make his/her own decisions and live with the outcomes .

[Al]

Originally posted by darkstar

Bovs have their place both on the street (emissions and also keeping the car a sleeper if its Plumbed back) and on the track (when running high ( 30psi +) boost pressure ).  Wank factor externally venting valves have no placement for any performance gain, but a plumbed back can certainly add benefits when done correctly.

COULD NOT AGREE WITH YA MORE!, well said. :uh-huh:

[darkstar]

Thanks for the reply Al.

In regard to the Emissions issue with no bov, the AFM isnt 'smart' enough to measure which direction the flow is in. Backwards or forwards, it cannot tell the difference, as the AFM is a hot wire element (think average light bulb) that measures the resistance as the wire cools. More air = more cooling, and hence a richer mixture as the afm communicates with the ECU.

I have made a flange for Mena (hehehe) to block the bov and the vacume lines etc. He wants it done because he thinks the standard bov is leaking boost back into the plumb back system (the valve is quite weak, too easy push it in with your fingers) and also for the noise (VL Turbos are famous for it). I think he is planning on upgrading to a bigger turbo, whether it be a highflow or a different unit entirely. If there is any premature wear on the turbo due to running no bov we can report back here and also inspect the rear cermaic wheel.

Ive got a hunch that the cermaic wheel will not fail due to compressor surge, even if was had no bov all its life, but from wear and tear or high boost, as we know the epoxy glue that holds the ceramic wheel on the steel shaft either fractures or expands at different rates at high temperatures, causing the shaft to spin out of control at 100,000rpm and shatter into peices. The exhaust wheel is ceramic, whilst the compressor wheel is steel.

Will report on progress with running no bov when the flange is installed.

Regards