Pros & Cons Of Not Running A Bov

[bigmikespec]

Mmmmm,

Just thinking about all the money that car manufacturers have wasted incorporating BOVs or compressor by-pass valves into their cars over the years..A BOV probably adds $50-150 to the build cost of each car. Millions of dollars wasted all because their engineers were liars....Can't trust those engineers!!!

How did you know I was an engineer? lol

2:1 is a basic engineering "standard" or guideline it was just a bit of a pot stir. To be honest I doubt whether no BOV will make a difference to turbo life at all, depending on what boost spike you would get, just more load on the bearings. I probably would on a ball bearing turbocharger as the bearings are not designed for very high axial loads. But for bush bearing cores (which can be rebuilt for peanuts anyway) I would not bother.

My opinion...

[**RB2530**]

thanks for all replies, no used to have GTR i now have R34 RB25det neo. with brand new gt3076 on 18psi, nisstune ecu with AFM

my plan is to install the new FMIC, forward facing plenum, throttle body and piping, i will get all the fittings welded to the pipe but not run a BOV. i will test it and see how i like it and if i need it i will quickly be able to connect the BOV, plan is to connect it in just after the FMIC behind front bumper and vent it to atmos, hopefully no one will see it down there....

there are a few pro's of not running one i can see, cant get defected and cost.

con's to much dispute between them, I mean i asked my mech/tuner and he said doesnt matter which way you go wont hurt the car ( by this i guess you gotta keep in mind its a heavily modified car its like sayying you 1000hp drag cars motor wont last as long as yur holden astra's motor)

my concern is throttle on, then off the throttle (say pulling up to stop lights) and it stalls.

I don't know much about the Neo ECU but what I do know is that with any AFM setup and a vent to atmosphere BOV, stalling issues are caused by the fact that when you close the throttle, the BOV is pulled open (all the ones I have used anyway) by the inlet manifold vacuum. The air drawn by the engine for idle and very light engine loads is then drawn in through the open BOV and not through your air filter and therefore the afm does not register that air. Obviously the extent to which this happens depends on where the BOV and air filter are in relation to each. Also depends on air filter restriction etc..

Also consider the fact that when you have 'vented to atmosphere', some air that has already passed through the AFM is dumped. So the ECU is calculating for air that the intake system no longer has...if this makes sense.

I advocate plumb back all the time. I wont say anymore.

With some smart tuning however you may get a driveable set up but if you want 'vent to atmosphere' consider a MAFless system.

[Adriano]

Basically having the AFM means you should run the BOV recirculating, I have had a non BOV car for a number of years, and the thrust surfaces of the bearing were worn, probably excessively by the "dose" as the spinning assembly goes back and forth. However the turbo is many years old, runs 20 psi, so it certainly hasnt "failed"

[89CAL]

I think the main reason that skylines run bov's anyway is because the run ceramic wheel turbos. Which from what I understand suffer more from failure due to heat and shock loading. There was alot of debate about the whole holding boost between gear changes or whatever it was but I think the point of it is to maintain the speed of the turbine rather then maintaining boost. For example, non bov creates backpressure through the turbo decreasing the speed of the turbine where venting the pressure retains the speed of the turbine so it can create boost again quicker.

Thats me trying to be techincal about it, thats just things from my understanding. Could be 100% wrong or 100% right im not claiming to know everything

[Fordy85]

thanks for all replies, no used to have GTR i now have R34 RB25det neo. with brand new gt3076 on 18psi, nisstune ecu with AFM

my plan is to install the new FMIC, forward facing plenum, throttle body and piping, i will get all the fittings welded to the pipe but not run a BOV. i will test it and see how i like it and if i need it i will quickly be able to connect the BOV, plan is to connect it in just after the FMIC behind front bumper and vent it to atmos, hopefully no one will see it down there....

there are a few pro's of not running one i can see, cant get defected and cost.

con's to much dispute between them, I mean i asked my mech/tuner and he said doesnt matter which way you go wont hurt the car ( by this i guess you gotta keep in mind its a heavily modified car its like sayying you 1000hp drag cars motor wont last as long as yur holden astra's motor)

my concern is throttle on, then off the throttle (say pulling up to stop lights) and it stalls.

when i put my silvertop rb20 into my 31 i chucked on a new fmic and front-facing plenum too so my mechanic made up all new ic piping (with no bov), we ran the afm in the original position and i found the car would go a bit flat after boosting then lifting off, which im guessing was the afm remeasuring the air that went back through the turbo and pod. asked my mechanic to put the afm between the fmic and plenum and problem solvered, afm now only measures the air getting past the throttle body and drives far smoother than before, especially when cold where it would boost a little strangely. not running a nistune as planned yet but once i get the car back with it's new turbo ill have nistune installed and mixtures checked, im not sure if the afm's signal is much different but safer to be sure. hope that helps!

[**RB2530**]

+1. Best post in this thread. Someone has a B.E.

Adam..you are correct...and you? It takes one to know one?

[**RB2530**]

I think the main reason that skylines run bov's anyway is because the run ceramic wheel turbos. Which from what I understand suffer more from failure due to heat and shock loading. There was alot of debate about the whole holding boost between gear changes or whatever it was but I think the point of it is to maintain the speed of the turbine rather then maintaining boost. For example, non bov creates backpressure through the turbo decreasing the speed of the turbine where venting the pressure retains the speed of the turbine so it can create boost again quicker.

Thats me trying to be techincal about it, thats just things from my understanding. Could be 100% wrong or 100% right im not claiming to know everything

Don't nearly all modern factory turbo cars run a BOV??..Europeans such as SAAB, Audi, Porsche, VW etc call it a 'compressor bypass valve'. They all use a Bosch item. Its what I use. I rate them, although there are a few forum members who claim they don't work. I must get special ones..

[**RB2530**]

Wasn't there some interesting proof regarding this topic coming through today???

[MBS206]

I don't know that a turbocharger core would have a 'design factor' of 2???

ie stock Nissan RB25DET T28 stock application is 7-8 psi..They run fine at 14-16psi?? No

The concensus is that they are 'ok' up to 11-12 psi and even then will not live a long life. So design factor is more like 1.5

The problem being it isn't seals or bearings that are failing in that position.

It is the RPM of the wheels exceeding limits and too much heat, making the ceramic explode.

Throw steel wheels in, change nothing else, those turbos run perfectly fine at 20PSi...

[MBS206]

Mmmmm,

Just thinking about all the money that car manufacturers have wasted incorporating BOVs or compressor by-pass valves into their cars over the years..A BOV probably adds $50-150 to the build cost of each car. Millions of dollars wasted all because their engineers were liars....Can't trust those engineers!!!

Ah yes, but why do car manufacturers install them?

Ask the designers... It has NOTHING to do with turbo life...

The BOV was developed to meet what? Emmisions!

Who was the first person to claim it damaged turbos? AFTERMARKET BOV MANUFACTURERS!

Oh, and the whole slow to build boost with no BOV.

I run a large turbo, so maybe you'll claim it has lots of KE to keep it spinning... Hence, I don't drop boost like others do.

But then, the really small turbos don't drop boost between shifts either when not running a BOV... Do you know what does? SHITTY SETUPS!

[**RB2530**]

Ah yes, but why do car manufacturers install them?

Ask the designers... It has NOTHING to do with turbo life...

The BOV was developed to meet what? Emmisions!

Who was the first person to claim it damaged turbos? AFTERMARKET BOV MANUFACTURERS!

Oh, and the whole slow to build boost with no BOV.

I run a large turbo, so maybe you'll claim it has lots of KE to keep it spinning... Hence, I don't drop boost like others do.

But then, the really small turbos don't drop boost between shifts either when not running a BOV... Do you know what does? SHITTY SETUPS!

So car manufacturers install BOV to meet emmisions???? How does that work?? Are you getting confused between vent to atmoshpere and recirculating?

Were aftermarket BOVs created before OEM ones? Contradiction in terms? IMO aftermarket BOVs are made to satisfy the ever growing rice market out there..

Your large turbo would have higher KE...but it would also have more surface area on the impeller vanes (it moves more air right?) so the advantage backpressure would have over the impeller with respect to stalling it would be higher right?

Now you have some proof that using/not using a BOV makes no difference to compressor stalling....but it does slow down right? Isn't the difference between it slowing down and stalling just a matter of time?

Where is your proof? Please provide detailed explanation?

[89CAL]

yeh i agree, i dont think BOVs are on there just for emmissions considering that if I had no BOV on my car it would still dispose of the wasted boost the same way - back through the air filter. theres no other way for it to vent to atmosphere.....

BOV's serve a purpose, im not saying they are necessary for a turbo car but they do serve a purpose

[D_Stirls]

This is compressor surge, full load compressor surge is what kills turbos. As has been said, once the TB has been closed to only load that the compressor will see is due a pressure wave bouncing back and forth through the intake tract (where the flutter noise comes from, it differs from what you will hear below) and as well as inertial. This is due to there being minimal turbine flow.

I think that with MAF based ECU's that a lot of the reason BOV's were fitted was because of emissions. This is highlighted by the early versions for some common engines (RB20, CA18, etc) not being fitted with BOV's but by the 90's when emission became tighter then BOV's began springing up on almost all turbo'd variants.

Edited March 23, 2010 by D_Stirls

[Harey]

So car manufacturers install BOV to meet emmisions???? How does that work?? Are you getting confused between vent to atmoshpere and recirculating?

Were aftermarket BOVs created before OEM ones? Contradiction in terms? IMO aftermarket BOVs are made to satisfy the ever growing rice market out there..

Yes to meet emissions. A plumb back bov is the only way to ensure you are not releasing air to the atmosphere without going through a catalytic converter. No bov and you are still releasing air to the atmosphere.

Aftermarket and OEM bovs have different goals so whichever one came first is irrelevant. OEM bovs for emissions. Aftermarket for noise and to supposedly protect your turbo.

[89CAL]

Yes to meet emissions. A plumb back bov is the only way to ensure you are not releasing air to the atmosphere without going through a catalytic converter. No bov and you are still releasing air to the atmosphere.

Aftermarket and OEM bovs have different goals so whichever one came first is irrelevant. OEM bovs for emissions. Aftermarket for noise and to supposedly protect your turbo.

Im sorry i still dont see how having no blow off valve is any different to having a plumback bov emissions wise..... atmo yes i can see that it vents to the atmosphere... but a plumback bov vents the air back to just in front of the turbo and then out the air filter, and no bov would mean that the pressure would go back through the turbo and out the filter anyway....

Im not having a go I'm just saying how it is to meet emissions. If you can explain then im more then happy to learn something

[MBS206]

So car manufacturers install BOV to meet emmisions???? How does that work?? Are you getting confused between vent to atmoshpere and recirculating?

Were aftermarket BOVs created before OEM ones? Contradiction in terms? IMO aftermarket BOVs are made to satisfy the ever growing rice market out there..

Your large turbo would have higher KE...but it would also have more surface area on the impeller vanes (it moves more air right?) so the advantage backpressure would have over the impeller with respect to stalling it would be higher right?

Now you have some proof that using/not using a BOV makes no difference to compressor stalling....but it does slow down right? Isn't the difference between it slowing down and stalling just a matter of time?

Where is your proof? Please provide detailed explanation?

Running a BOV, the compressor slows down as well right? If it doesn't... You might want to look into patenting the BOV and turbo setup as a perpetual motion machine. It's ALWAYS going to slow.

Put a car on a dyno, run it up full tilt, make it "dose" with no air filter on and watch the turbo... The turbo will NOT stall. Simple test for you. Go on, go try it. Film it to with a super high frame rate so we can slow it down too, that'd be awesome. Thanks.

As to the post I'd made, I can't find it at the moment, but I've made it around 5 times on this forum, a rather long read. Go have a look if you would like.

Also, most of the failures people seem to have, that are blamed on no BOV are exhaust side oil seals... Now if all the pressure is on the inlet side... Shouldn't that side go kaboom first?

And yes, the BOV was first bought about for emmisions reason. When a turbo "doses" air rushes backwards and forwards (As a sound wave does, hence the ptsususus) and this makes AFM metered cars go "Oh my, lots of air" which means lots of fuel, which means high CO emmisions. Have you noticed how the turbo had been around for YEARS and then as emmisions got tighter the BOV was introduced?

And a vent to atmosphere BOV causes the same issue emmisions wise as not running a BOV.

Look at all the late 80s turbo cars... They DON'T RUN BOVS... Are they known for killing turbos? No. Why? Because not running a BOV doesn't kill a turbo. What happened at the end of the 80s start of the 90s? Emmisions got tighter... What happened then? recirculating BOVs were invented... What happened then? some wanker invented atmospheric venting BOVs and started a rumour that not running a BOV caused damage to turbos...What happened then? By this time we're heading for the late 90s early 00s, and 15 year old turbos with over 250 000KM on them start dieing from old age... Mainly seals, or ceramic wheels... People view this as an issue created from these cars not having a BOV... The funny part... The cars with BOVs are all failing the same way too now... Just no one can see it!

If a car running a BOV, vs when it never ran a BOV comes onto boost exactly the same between gears... Does it not show you that the compressor is not stalling/slowing any quicker then when it runs a BOV?

Have you done any testing, or are you being a text book mechanic?

I run currently a fairly old turbo, that yes,needs a rebuild as the exhaust side oil seal has started letting oil out under high oil pressure, but the funny thing... There is NO shaft play in this turbo... And it's got a SHITLOAD of KMs on it... And it's never ran a BOV... (And I punish it at the track, it's not a daily driver, or even a weekend warrior, it goes to the track, and back)

[D_Stirls]

probably shouldn't use the word stall, With Compressor design/operation stall means something else.

Edited March 24, 2010 by D_Stirls

[MBS206]

probably shouldn't use the word stall, With Compressor design/operation stall means something else.

A stail in compressor terms, from what I know in proper design operation is that the compressor continues to spin, but the air flow around it "stalls" much like when a plane stalls... Whilst the angle of attack is for "lift" it actually falls.

Stalling when people are talking about not running a BOV they're meaning the actual compressor "stalls" or stops.

To claim it stalls in the matter of air flows in the incorrect direction to what it should considering compressor movement is correct. And this is how we get the ptsusususu noise. The air flow turns backwards to the direction the compressor is moving it, forcing "high pressure air" out the air filter. The forces applied from the compressor then overcome the stall, forcing it back into the inlet piping. (Leaving a now nearly the same size low pressure area behind it, but not quite, so we have one high pressure "pulse"). Then the pressure builds up too much, flow reverses, and the process continues over and over, causing a high pressure, low pressure, rinse repeat of air flow out the air filter, and a then Ptsususususu... Of pressure fluctuations...

[Dose Pipe Sutututu]

well said MSB206!

I run a bov with a piece of rubber wedged between it so it looks legal

other than that flutter on baby!

all day, everyday 1.3bar, still haven't seen my old school turbo go kaboom either

[**RB2530**]

Aw FFS!! Nobody is saying that turbos go kaboom if you dont run a BOV!!! I am talking about long term wear on bearings and not catastrophic failures.

By the sounds of it you guys are both running 'bush' bearing turbos???..So maybe your experience is based on those. Bush and Ball bearings can tolerate different levels of thrust loading. I think someone else in the thread supports this?

Matt,

As far as perpetual motion machines are concerned, your theory that reduction in turbine rpm is the same irrespective of BOV /NO BOV, to me, has a scent of divine energy creation in itself...

By what you were saying I assumed 'you' had some measured data to support your theory. I was keen to see it.

Onve agin very very simply put;

On a gear change the only energy remaining in T/C is kinetic. Turbine starts to slow due to friction in brgs and windage etc. With no BOV, as soon TB closes there is a rise in pressure between it and the compressor.

Now, where do you think the energy that compresses this air comes from??

Something else I will put out there. Another energy sink within the whole intake system is the restriction of the air filter and pipework leading up to the compressor. Typically the compressor draws air through this section of the intake and as a result, the pressure at the compressor inlet will be slightly -ve. (if you don't accept this I think I will call it a day-we must be using different brands of physics)

Now consider that with a recirc BOV, the air is dumped back into the intake. So pressure within the intake will become slightly +ve and will therefore act to remove the intake restriction and IMO reduce the loss in turbine rpm...