Pros & Cons Of Not Running A Bov

[3LGODZILA]

i ran no bov for a while and the car ran so much better with one, i also noticed the difference between stock and atmo.

also recently blew my standard turbo (bearings) and when u consider how a turbo operates and what happens when theres no bov, it cannot be doing the thrust bearing any good. wudnt be surprised if that was the cause of failure

my 2 cents anyway

[R31Nismoid]

Lets consider for a minute the fact that most race cars don't run a BOV.

Let's all consider that turbochargers between meetings are rebuilt

Race cars most of the time are bad bad examples.

BOV or no BOV comes down to two questions... one Adriano said earlier.

1. What ECU?

2. MAF or MAP?

Everything else in this thread apart from the above two questions is largely irrelevant unfortunately.

[PM-R33]

I thought my post was relevent

[snozzle]

i really dont see how compressor surge can damage a turbo, ive blocked off the stock bov on alot of cars ive owned and ive never seen any added shaft play from when ive owned the car to when ive sold it (roughly 40,000kms)

ppl will claim it causes turbo failure eventually but ive seen alot of turbos fail running the standard bov.. so just coz a turbo failed with a blocked bov doesnt mean its the cause

If you like the sound of compressor surge, block off you bov. If you prefer the sound of a bov whether it be atmospheric or plumbed back, go for that, i dont believe it will affect the reliability of your turbo and hurting your engine is out of the question.

Performance wise - on a stock ecu that has not been tuned; it may cause the car to run abit richer and pop occasionally so its also important to know what ecu you will be running aswell. If its stock ecu, stick with the stock plumbed back bov car will drive smoother but if its going to be tuned, decide before you get it tuned so that its tuned accordingly.

[SKYPER]

Interesting subject.

Nismo didn't run stock BOV's on their 24hour R35GTR racecar (didn't hear about a turbo failure and can't hear any compressor surge) -

http://www.viddler.com/explore/GTRBlog/videos/47/

Photo of Nismo 24hour R35GTR engine bay without stock BOV's -

http://www.gtr-world.net/media/4/20080706-02-001.jpg

But transmission seems to shift quickly on R35GTR, so probably keeps turbo's spooled up during gearchanges. Also I have read somewhere that the stock R35GTR turbo's are non ballbearing (non ballbearing turbo's can run without BOV's).

Cefiro RB20DET engine didn't have a BOV, but had non ballbearing turbo, etc -

http://www.flashoptions.com/i_prod/cefiro%20RB20%201.JPG

R32 RB20DET had ballbearing turbo and BOV.

Edited March 21, 2010 by SKYPER

[snozzle]

i dont understand the logic of "atmospheric bovs are to keep your boost up between gear changes" when they actually dispel the charged air out of ur system quicker than a system with no bov...

[r33_racer]

isnt it due to the belief that the air in the system is basically trying to slow/stall the turbo down/out after it hits the closed throttle body and goes backwards? Hence the bov's job to dispel that air or recirculate it back to the intake of the turbo. Well thats what they say....

[greensa14]

Yea but there would still be some pressure in the system. Whereas expelling to atmosphere relieves all the pressure hence the turbs having to spool up and build boost again.

If ya like me you probably get bored anyway and are constantly changing set ups.

[wlspn]

skyper, rb20s did not come factory with a ball-bearing turbo

[scotty nm35]

With no bov, as the boost raises to maximum pressure when the throttle is closed, there is maximum load on the compressor and the thrust washer. This will obviously cause more wear and slow the shaft down.

From what I can work out, when the compressor surges, the shaft is vibrating in the journal/ball bearing causing axial load and wearing them.

Im guessing its better to run a bov even in a race car, although only half the historic cars I saw yesterday were running them. If properly tuned with a map sensor you could perhaps use the boost spike to get a bit of extra punch for the next gear?

[MBS206]

With no bov, as the boost raises to maximum pressure when the throttle is closed, there is maximum load on the compressor and the thrust washer. This will obviously cause more wear and slow the shaft down.

From what I can work out, when the compressor surges, the shaft is vibrating in the journal/ball bearing causing axial load and wearing them.

Im guessing its better to run a bov even in a race car, although only half the historic cars I saw yesterday were running them. If properly tuned with a map sensor you could perhaps use the boost spike to get a bit of extra punch for the next gear?

Wrong... Look at the design of the impellar. It's uni directional. Ie only forces acting in one direction will make it turn.

Running no bov causes laggy gear shifts if the pressure source for wadtegate is on the ic piping not the manifold. As the wadtegate stays open and no gases are turning the turbine.

When I get home I'll dig up some info on why it won't cause damage and the lies people spill about them

[**RB2530**]

Wilkor32gtr,

Unfortunately mate you will not get a straight answer to this question on these forums. It has been debated for many years on these forums and comes up every few months. The pros and cons vary and actually depend many variables.

The 'keyboards mechanics' out there have an endless number of anecdotes of cars that don't run BOVs have no problem. Race cars etc etc. Race cars are also not trying to get the best possible life out of their turbochargers though. (I assume you will be).

Fact is some race cars also don't run cooling fans. But I can't ever remember seeing traffic lights and peak hour traffic on a race track. It really is a horses for courses thing.

IMO, for a street car setup, a BOV is a very good idea for both turbocharger longevity and driveability.

[scotty nm35]

Wrong... Look at the design of the impellar. It's uni directional. Ie only forces acting in one direction will make it turn.

Running no bov causes laggy gear shifts if the pressure source for wadtegate is on the ic piping not the manifold. As the wadtegate stays open and no gases are turning the turbine.

When I get home I'll dig up some info on why it won't cause damage and the lies people spill about them

The shaft still has plenty of potential energy considering it is spinning at 100,000 revs plus, no amount of wastegate actuation is going to change that. What exactly is wrong?

Any boost causes wear on the thrust washer and the higher boost you run, the more force on it. What boost is seen at close of throttle with no bov? 40, 50 psi?

There are no "lies" being spilt, and no reason to discredit people for trying to help.

[MBS206]

The shaft still has plenty of potential energy considering it is spinning at 100,000 revs plus, no amount of wastegate actuation is going to change that. What exactly is wrong?

Any boost causes wear on the thrust washer and the higher boost you run, the more force on it. What boost is seen at close of throttle with no bov? 40, 50 psi?

There are no "lies" being spilt, and no reason to discredit people for trying to help.

Well one huge thing people keep claiming is that the compressor stalls, a lie right there. Yes they slow, just as much as a turbo with a bov.

[**RB2530**]

Wrong... Look at the design of the impellar. It's uni directional. Ie only forces acting in one direction will make it turn.

Running no bov causes laggy gear shifts if the pressure source for wadtegate is on the ic piping not the manifold. As the wadtegate stays open and no gases are turning the turbine.

When I get home I'll dig up some info on why it won't cause damage and the lies people spill about them

I agree about the unidirectional thing. The direction of the force acting on the impeller vanes does not change. The rest of what you say I can't..

1. Normal operating conditions where impeller is being spun by turbine. Air is drawn in at compressor inlet and starts to rotate with vanes. Air moves outwards through impeller (due to centrigual acceleration) and is captured by compressor scroll. Curvature of vanes acts to add tangential velocity to air as it moves into scroll. Velocity is in direction of air rotation in scroll which increases efficiency.

2. Under a reverse flow scenario, the air enters the scroll and obviously starts to rotate with it. As the cross section of the scroll reduces, the air is pushed into the vanes and starts to rotate them. The centrifugal force that is wanting to push the air back out is simply counteracted by the pressure in the scroll. You can prove this by getting an old turbo and putting compressed air into the compressor outlet. Believe it or not the compressor wheel spins backwards!!

Also if you have a look at the geometry of the turbine, this is exactly how it works!! ie exhaust gas enters the scroll and turns the vanes. The only thing that changes is the vane geometry (curvature is the same though).

Now we need to go back to basics..

When engine is running under boost the turbine is being spun by the exhaust gas. The turbine spins the compressor wheel and it compresses the air. On a gear change all positive pressure disappears from the exhaust manifold. It may actually be slightly negative due the fact that the exhaust gas flowing in the exhaust has inertia and wants to keep moving...

So when the throttle closes there is no exhaust pressure to spin turbocharger because engine is not burning fuel. The only thing that is keeping it spinning is its own 'Kinetic energy'. It does not matter what the WG is doing.

Without a BOV you have air pressure remaining in the compressor outlet which is trying to spin the comp wheel backwards and no energy from the turbine to counteract it (due to no exhaust gas pressure). It 'will' slow down quicker than it would if there was no pressure at the compressor outlet.

Now as far as damage is concerned..There is confusion between wear and damage. Wear is a type of damage that occurs over time in an expected fashion. If a bearing gets through 15% of it expected life is it worn out or damaged? If it gets through 110% of its expected life is it worn out or damaged?

What is known with certainty is that the life of a bearing is generally inversely proportional to its loading (all other things being equal)...The higher the loading, the quicker it fail. The is a very simplistic view but it gets my point across. Also if you are running 5psi and typical spikes were up around 15psi no issue. If you are running 25psi with spikes up to 50psi there may be an issue..

So when you dont run a BOV and you load up the thrust bearing more than what you would with a BOV, and it fails after 25,000km you may find it acceptable and call it worn out..If you were hoping for 100,000km then you would say its damaged....

[bigmikespec]

If you are running 25psi with spikes up to 50psi there may be an issue..

Not with a 2:1 safety factor in the design.

[**RB2530**]

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!!!

[MrStabby]

Now we need to go back to basics..

When engine is running under boost the turbine is being spun by the exhaust gas. The turbine spins the compressor wheel and it compresses the air. On a gear change all positive pressure disappears from the exhaust manifold. It may actually be slightly negative due the fact that the exhaust gas flowing in the exhaust has inertia and wants to keep moving...

So when the throttle closes there is no exhaust pressure to spin turbocharger because engine is not burning fuel. The only thing that is keeping it spinning is its own 'Kinetic energy'. It does not matter what the WG is doing.

Without a BOV you have air pressure remaining in the compressor outlet which is trying to spin the comp wheel backwards and no energy from the turbine to counteract it (due to no exhaust gas pressure). It 'will' slow down quicker than it would if there was no pressure at the compressor outlet.

Now as far as damage is concerned..There is confusion between wear and damage. Wear is a type of damage that occurs over time in an expected fashion. If a bearing gets through 15% of it expected life is it worn out or damaged? If it gets through 110% of its expected life is it worn out or damaged?

What is known with certainty is that the life of a bearing is generally inversely proportional to its loading (all other things being equal)...The higher the loading, the quicker it fail. The is a very simplistic view but it gets my point across. Also if you are running 5psi and typical spikes were up around 15psi no issue. If you are running 25psi with spikes up to 50psi there may be an issue..

So when you dont run a BOV and you load up the thrust bearing more than what you would with a BOV, and it fails after 25,000km you may find it acceptable and call it worn out..If you were hoping for 100,000km then you would say its damaged....

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

[**RB2530**]

Not with a 2:1 safety factor in the design.

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

[.WILKO.]

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.