No Bov, And Turbo Life-span

[Gts-t]

on a MAF equipped car the BOV was used for emissions.

it avoids over-fuelling in a MAF based application

end of story

A bov is not fitted to control emissions. It is designed to keep the turbo spinning when the throttle is closed, not slow it down and prolong its life in the process.

Also i have the problem of my car stalling occasionally, i never had it before i fitted an atmo bov

[rb26s13]

funny all this talk of BOV : i went to enquire about getting a blueplate/roady on my car for the conversion.. the guy strictly instructed that i have no BOV on the car regardless if it was plumback or atmo.. so stuffed if i know :

Edited June 10, 2006 by rb26s13

[SuAvE-1]

i know i've run an atmo blow off valve without any sort of stalling or Bs. Just gotta make sure you cap the intake pipe properly to prevent any measured air from escaping (thus running less air compared to fuel).

I do agree blow off vales save compressor wheels. Not so much when you occasionally give it to the car, but at the point where the turbo is glowing hot and relatively mallable, having a ton of air wack up against the turbine blades will bend them back and forth and weaken them till they snap.

Now, i hear a lot of people say that the computer is supposed 'account' for the vented air going back into the intake... if you are not accelerating, how are you supposed to be running rich?????? there is no accounting for shit because you have let go of the accelerator. By the time you resume acceleration, the vented air has dissipated along with the atmospheric air/ or what has been sucked in by the turbo.

There is a fixed amount of air between the intake of the turbo and the air filer and all that piping in between. when the excess air is blow off back into the intake, it will not go into the turbo (because as the throttle is closed there is really no pressure to allow it go in there) so it will push out the air which is around the air filters until it is ready to be sucked in.

Basically, when you plumb back, i reckon you are still technically venting to atmosphere. It doesn't make sense that you will run rich because you are not accelerating. I know I haven't had any issues with an atmo blow off valve.

Blow off valves are good, either atmo or plumb back, because they save your turbo from counter forces and still allow it to spin freely and with the left over momentum, build up boost quicker. The only time i'ver ever seen people run rich and have their cars stagger is when the have a massive air/pressure leak after the AFM causing the engine as we all know to not recieve the air it has percieved for the amount of fuel it is getting. Too rich...we all know what happens. you must block the pipe off properly.

Did i miss something? This is just my theory on what happens, correct me if i'm wrong.

[psybic]

I've run: ATMO BOV, Half half, and full recirc, as well as none. Never had stalling problems, never suffered from excessive lag due to the change.

It must help the life of the turbo. A turbo timer must help the life of the turbo aswell... by how much, is it always required for all applications?

How many VL Turbos have failed? How many GTR turbos have failed? You always get failure and because the arguements go on with no super clear answer, I'd say do what you feel, each to their own.

[Josh]

I really do think its a pointless argument.. just like all those Turbo Vs. V8 discussions.. I run no BOV and have only had minor issues - Eg: Stalling - Admittedly this has not happened very often and have been told by a reputable tuner that it could be due to having my speed cut wire cut..) My car is a daily driver/track car and gets the crap flogged out of it reguarly... It all comes down to personal preferance really... Some say its bad (Although I'm still waiting for documented proof of turbine failure directly related to it..), Some people, like myself, say its fine - I'm basing this on personal experience and the experience of others I know who run no BOV and have done for a long time with no problems..

Mikey just do whatever dude..

[RB SANDY]

What do you say about having a bov spring Adjusted tight so it takes the big pressure build up off the turbo and still keaps the response in the gear change I have run my car with no bov and there is a difference more low end response and at hi speeds eg 3th 4th gear more power and a big difference in the gear change it realy kicks. I am running 11psi could the stock bov be leaking.

ps, the bov spring Adjusted tight setup might sound good you get the pssshhhtt and the dose.

[bilbo117]

hmm...

Big thread to read, lots of long posts.

I dont pretend to know much but one thing that interests me is that people say when the throttle body is closed the turbo is faced with huge pressure trying to push through it.

The air thats forced backwards against the turbo can be no greater then the pressure that the turbo has created. ie, 12 pounds of boost means, with the throttle body closed, there is no more then 12 pound of boost in the piping between the turbo and the throttle body (doesnt sound drangerous to me at all and no different from when the throttle body is open).

so, for no BOV to be detremental to turbo life, I would assume that it is because of one major factor.

The turbo is always driven from the exhaust gases. I assume the bearings, shaft, impeller etc are all designed only for this one directional loading. When you close the throttle body, you have a lack of exhaust gas pressure and a relatively high intake pressure acting backwards on the impeller. Perhaps this causes some kind of weird unbalance?

/end rant

[TurboX]

I could be wrong but I would have thought that the opinions of the Owner of one of Australias forefront Nissan developers & modifiers for more than 10 years could have some credibility!

NIZPRO have the runs on the board with most Turbocharged engines including RB's and lately Ford Turbo's with one running over a thousand HP I belive.

Simon has some unique beliefs, but until some of you have the resources he has and the experience in the industry, I will tend to keep an open mind on what he proposes.

[Beer Baron]

i run two atmo vented bovs on my car. never had it stall once. it idles smoothly at 900rpm and that is with a tuned pfc and adjusted cam timing. so it certainly can be done without problems.

[RB SANDY]

My car used to stall with the BOV on

[TTT]

Paul – you don’t want to tear it to shreads but I have time today…

So in the first part of his description of a bov he says

"The blow-off valve is designed as an emissions control device for OE manufacturers. It came about when smaller engines made more and more power using larger turbochargers and bigger intercoolers. As you close the throttle, the build up of pressure and the larger volume inside the intake has to go somewhere; it can't go into the engine because the throttle is shut. Instead, it has to do a U-turn and it comes screaming out the airflow meter. That creates the 'gobble-goggle' sound.

"The gobble-gobble sound is something the public has grown to love.

Basically describing what happens without a bov and why the bov was created/used… to prevent this gobble gobble as he calls it.

But then he goes on to a conversation that they have with customers saying..

"Unfortunately, we've had people ringing up and wanting the "audible gear change alarm".

""What audible gear change alarm?" we ask. "You know, when the Sierras were running around and just when they went to change gear it used to go whoda-whoda-whoda" they tell us.

""No pal, that is the dump valve..."

So first he says not having a bov/dump valve/recirculation valve will create the sound “that the public has grown to love”, then tells the customer that ""No pal, that is the dump valve..."

Go captain Contradiction go!!!...

Next bit of BS.

"We've tested one on a manual gearbox performance car run at Winton Raceway. I think it was running 1 minute 40s back then, but it would lose 2 seconds a lap putting the gobble-gobble valve on.

Again he calls the bov/bypass valve/recirculation valve, a gobble gobble valve when in an earlier statement he explained the sound is caused from NOT having a bov.

CONFUSED WOULD WE???

Lets get something clear here..

The 2 examples he has made in his little blurb are refering to a track car, that is raced, that is setup and tuned for circuit racing.

The other is of a world rally car, which is raced, set up for rally racing.

His first example

"We've tested one on a manual gearbox performance car run at Winton Raceway

I’ve got no problem with it.

If you have a dedicated race car that you ONLY drive at a track, constantly caning it trying get the quickest lap times, then go right ahead and use no bov.

But if you then have to drive the thing home, to the shops, on public roads etc, you are going to put up with all the associated problems that come with having an AFM car that is getting double the air intake reading from the AFM like he states in this quote.

"The airflow meter is not all that smart and does not realise the air is going in the wrong direction; it therefore measures the air twice (once going into the engine and again going out in the wrong direction). The computer now tips in twice as much fuel as what's required, making it run rich - making it not pass emissions.

Forget emissions for a second, this rich mixture has plenty of issues on a street car.

1.) backfire sounds

2.) stalling

3.) black shit all over your rear bar around the exhaust.

4.) Jerky feeling when you are cruising with very little on off throttle.

His second example.

A world rally car is not what us skyline owners have.

We do not have a budget that allows us to replace a $40K turbo after each race (yes rally cars have turbo’s that cost around $40K, purpose built to work with the restrictor they have to run, which they bin after each race wether it is still working perfectly or not)

He also seems to have forgotten a little thing that rally cars have … ANTILAG.

When they come off throttle, you also hear a whole heap of backfire cause even with throttle closed, the turbo is kept spinning with antilag.

Why compare peoples street cars with those 2 examples?

It’s stupid.

Will not having a bov break your turbo?

Can’t be proven.

The fact is, if you have an afm equipt car, having a plumback bov will make the car run better.

He says it himself

"The airflow meter is not all that smart and does not realise the air is going in the wrong direction; it therefore measures the air twice (once going into the engine and again going out in the wrong direction). The computer now tips in twice as much fuel as what's required, making it run rich

Having a plumback bov will prevent the above situation.

I also do not agree with his theory on throttle response.

1.) he says

. As you close the throttle, the build up of pressure and the larger volume inside the intake has to go somewhere; it can't go into the engine because the throttle is shut. Instead, it has to do a U-turn and it comes screaming out the airflow meter. That creates the 'gobble-goggle' sound.

So by his own words, this backed up air goes BACK THROUGH THE TURBO cause it goes back out the AFM which is further down the track of the intake system.

How he thinks that this does NOT slow the turbo’s RPM MORE than a plumback bov dumping the air back in front of the turbo inlet is just amazing to me. And absolutely stupid.

"The fact that people think that they keep the turbo spinning 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.

OK.. here I go. The theories of TT…

I agree with

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.

The problem with his theory is that wether you have a bov or not, plumback or atmo… when you shut the throttle it’s all the same. No exhaust flow as throttle is shut.

So this does not change wether there is any sort of bov or not.

My theory on no bov.

Throttle shut, air stuck in intercooler pipes, causes pressure build up and escapes through the path of least resistance… metal pipes and shut throttle butterfly is solid.

Turbo INLET blades are spinning but have gaps where air can escape so it goes back through there.

My theory on plumb back bov or recirculation valve.

Throttle shut, air stuck in intercooler pipes, causes pressure build up and escapes through the path of least resistance. In this moment where throttle is shut, manifold sees vacuum, this sucks the recirc valve open, air escapes through here and leads down the pipe to in front of the turbo.

Both of these scenarios end up with the pipes losing pressure, be it out the bov or out the turbo with no bov.

However, no one here (or the guy in the article) can surely argue that the no bov option of air needing to go back through the turbo will slow down the turbo more than dumping air in FRONT of a turbo which was sucking air in.

It’s seriously common sense.

So having said AAAAALLLLLL this… throttle response and with it boost response will be higher on a car with recirculating bov than a car with no bov.

I say, a turbo spinning at 100,000rpm will slow down MORE with no bov than with a recirc bov between gearchanges.

My reason as stated above is because of the air being forced back through a turbo that is spinning in a direction which is trying to suck air in, compares to a turbo that has nothing trying to go the wrong way, infact has the air that was in the pipes dumped back in front of it.

No force on the back of the COMPRESSOR of a turbo equals less turbo rpm loss between gears.

Has nothing to do with exhaust side of things.

And I’m spent.

[paulr33]

i agree with 100% and i still believe to this day the bov is purely to prevent compressor failure.

[mad082]

there are 2 point i want to make here. first is a quick and easy explanation of bov vs no bov.

imagine people walking through a turnstyle (people are the air, turnstyle is the turbo).

no bov- when the throttle is closed the air stops but is still at boost so it trys to escape. (the people start to walk back out through the turnstyle, however this doesn't actually cause the turbo to spin backwards, just slow down). then when you get on the throttle again more people are walking through the turnstyle, but there are people still trying to walk backwards so they have to turn around. this causes a slight delay.

with bov- same start, people walking through turnstyle. when throttle shut the people already though the turnstyle walk around the turnstyle and back through it and keep doing this till the throttle is open again. there isn't anyone walking against the turnstyle so when the throttle is opened everyone can keep on moving foward.

my second point is to do with the stock r33 bov. everyone seems to think it is the best thing since sliced bread. however how many of you have taken it off? those who have will have noticed that it has a hole that constantly leaks boost. now people who think that only aftermarket atmo bovs cause the car not to idle need to disconnect the plumback pipe and see what happens. it will barely idle, if at all. then put your hand over the bov hole and it will idle fine. this means that at full noise there is boost being wasted.

everyone i know with a r33 with an atmo bov have never had idle problems (1 guy has owned 3, all with atmo bovs with no problems). the only problems i have heard have been fixed by tightening the spring to stop it leaking boost. the cause of the idle problems is leaking boost. and as for the running rich on gear changes that is only for a split second. having driven a few r33s both before and after the atmo bov i can say that the extra dumping capacity of the atmo more than makes up for the richness. so if you have an atmo bov and the car doesn't idle, adjust the tension spring, or make sure it isn't leaking boost from around the base of it. and possibly check/change spark plugs. i had idle issues with stock bov due to crap plugs.

sorry for the hijack, but i feel much better now. thank you, and goodnight.

Edited June 13, 2006 by mad082

[mad082]

oh and the vl turbo was made before 1991 so different emissions rules apply to it. any car made before 1991 has different gas/noise emission rules, as well as other things. and there are more cars than the vl without bovs. and its not just emissions that bovs are for. they also improve the drive quality (less lag on gear changes).

and the proper name is compressor bypass valve, as has been said by someone here.

Edited June 13, 2006 by mad082

[FATGTS-R]

I have an 87 HR31 GTSR. No factory BOV, and it stalled. Fitted a bosch plastic jobby and all is fine.

Some people use the argument that when Nissan fitted BOVs to cars that turbo sevice intervals increased but its a flawed comparison as from what I understand ballbearing turbos were also first fitted when the BOVs came to be fitted. The extebded turbo sevice interval could of been solely because of the uprated technology of the turbo, or not, or both.

On the emissions side of things, nobody has yet taken into consideration the crankcase vapours. With no BOV, the oily non epa friendly vapours emitted from the rocker breathers go straight out to atmosphere via the airfilter.

With a recirc bov fitted the vapours remain in a sealed system and cant get out to atmo.

Surely, this was a huge part of Nissans reasoning for fitting them.

Fwiw, I am pro BOV and would always run one on a turbocharged vehicle beleiving it has to increase turbo life, but by how much I dont know. But for the purpose of this thread I do beleive it serves an emissions purpose as well to keep the crankcase vapours sealed in.

[bilbo117]

my second point is to do with the stock r33 bov. everyone seems to think it is the best thing since sliced bread. however how many of you have taken it off? those who have will have noticed that it has a hole that constantly leaks boost. now people who think that only aftermarket atmo bovs cause the car not to idle need to disconnect the plumback pipe and see what happens. it will barely idle, if at all. then put your hand over the bov hole and it will idle fine. this means that at full noise there is boost being wasted.

Hmmm I dont quite understand what you are saying here. If you disconnect the Plumb back pipe from the turbo of course it will not idle properly. at idle the intake is under vaccuam pressure, and will therefore suck un-metered air through the big hole you have left their. However, when connected all is good. because all air that passes through will be metered.

On a side note, I have my factory BOV with the small hole you talk of blocked. Not much of a difference at all in the running of the car... I read somewhere once this hole is for smoother deacceleration.

[mad082]

if you plug up the plumback pipe after you disconnect it it will still idle like crap. and i pluged up the hole in the bov and it wouldn't hold high boost.

Edited June 14, 2006 by mad082

[bilbo117]

if you plug up the plumback pipe after you disconnect it it will still idle like crap. and i pluged up the hole in the bov and it wouldn't hold high boost.

because it is still sucking unmetered air isnt it... through the hole in the bov.....

What is high boost for you? Mine holds 12 fine....

[mad082]

i'm running about 12-13psi. it would get high up in the rpm and bleed off to about 10psi. but i'm going to get an after market plumback bov. the other problem is that they only have to move a little bit before they leak.

[seriesII]

i like what: GTST said above. covered alot of everything in one post ..