BOV position

[doridori32]

but will blocking up this hole cause any damage to anything? cause i have an flat plate to block it off that was part of my old setup. just thinking that i might block the small hole off and take it for a run just to test the differences, but i dont wana do any damage to anything if i block it up....

cheers!

Stop wasting your time and damaging factory parts, remove the BOV and let it run naturally.

Petar.

[Sydneykid]

Oh no, the old "BOV's don't do anything" line .............

Why did Nissan fit them?

Why did the early turbo engines (someone used the NICS and RB30ET examples) not use them and had recommended turbo servicing at 60,000 ks'?

Why do the later Nissan engines have recommended turbo servicing at 120,000 k's?

Does anyomne really think that Nissan wasted money on BOV's, fitting something that wasn't necessary? They would have saved millions of dollars over the life of R32/33/34 and S13/14/15 and Stagea and Cefiro and ............you get the drift.

Does any out there really believe that comparing race cars with no BOV's and road cars is realistic? Give me a break, we service turbos every 2,000 ks' of racing. Personally I don't want to be doing that on my road car.

With a boost gauge plumbed to the comprressor housing you can easily see what happens to the pressure at the compressor when you close the throttle without a BOV, double the set boost limit is not unusual. Does any one really think that that is somehow good for your turbo?

Everyone has heard the turbo flutter noise when the throttle is closed and no BOV is fitted and noise = vibration at the tubine blades. Does any one really think that that is somehow good for your turbo?

As for slowing the rpm versus reversing the flow. On the engine dyno I have seen large amounts of air flow out of the compressor inlet on throttle close. That air is coming from somwehere and it has to get past the compressor blades to get out. So I have no problem with the thought that the compressor blades stop or turn backwards. Even if they only slow rapidly, does any one really think that that is somehow good for your turbo?

Sorry have to stop this post, there is a car on the dyno that needs me......

[R31 POWER]

Same as Roy I to fully shut(Greddy type S can be closed shut by that thread on top)my BOV to see what the sound would be like.Yes it fluttered it's tit's off and when nailing it and reaching for another gear it felt doughy/jerks and did'nt feel right when in the start of the other gear on boost.So it might not give power but better driveabilty is what it does.

[mattysaidso]

can anyone answer my question regarding blocking the small hole in the bottom of the factory BOV? and its damaging effect, if any to the rest of the turbo system? i just want to be sure i wont f*#k anything if i block it off and take it for a strap.

ps. i have decided to stick with my std bov cause i really dont have the $$$ to replace my turbo 'IF' it shits itself due to increased wear from compressor surge.

[Sydneykid]

can anyone answer my question regarding blocking the small hole in the bottom of the factory BOV? and its damaging effect, if any to the rest of the turbo system? i just want to be sure i wont f*#k anything if i block it off and take it for a strap.

ps. i have decided to stick with my std bov cause i really dont have the $$$ to replace my turbo 'IF' it shits itself due to increased wear from compressor surge.

The theory is the hole bleeds off a very small amount of boost when the airflow is low, so it smoooooths out the transition between no boost and some boost. It is really too small to lower the boost once the turbo is at its max airflow. So if you want a very slightly faster boost then block the hole. But you shouldn't expect a max power increase.

Hope that helps:cheers:

[Roy]

So i am pretty sure that the flow of air is reversed without a BOV, but i would have thought that the compressor would only slow not actually stop, let alone reverse.

Either way the loads on the tubine/compressor shaft is higher without a BOV then with a BOV...so thats enough reason for me...especially if you are running a std ceramic turbo, the heat combined with additional loads and vibration would be another POSSIBLE (I dont KNOW, just guessing) factor when thrashing around in your car.

[R33vit]

can anyone answer my question regarding blocking the small hole in the bottom of the factory BOV? and its damaging effect, if any to the rest of the turbo system? i just want to be sure i wont f*#k anything if i block it off and take it for a strap.

ps. i have decided to stick with my std bov cause i really dont have the $$$ to replace my turbo 'IF' it shits itself due to increased wear from compressor surge.

Matty it won’t damage anything if you block the little hole in the bottom of the stock BOV, but it will be difficult to feather the throttle especially in lower gears.

[pnblight]

People actually have proof they dont do anything, not proof they do ANYTHING.

Petar.

well thats a load of shit "Gramhan Bell who wrote Forced Induction" has alot to say about the reasons the bov were invented and used and it wasnt not for damage to turbos ,its primary role is to reduce back pressure on outlet of turbo to keep the turbo spooled up as long as possible so there is reduce turbo lag when you get back on the throddle. Just stop and think to your self if you reduce exhaust gas flow (throddle shut ) and get a hugh back pressure pike its going to try and stop turbo dead so when you get back on the throddle you have to spool up the turbo again (laggy as shit) . Where the turbo can handle this is irrelevant

[mattysaidso]

thanx guys for your responses, think i will just leave it as is. if i really get bored one day i might block it off just to test the difference.

ps. R33vit, what mods do you have on your 33 to get 1/4 mile time? it is f*#king great for a stock turbo!

[doridori32]

Yeh mate thats the THEORY, where is the prac like everyone else has to prove they dont do anything.

RACE CARS DONT USE BOV's!

FACTORY CARS DO FOR EMMISIONS!!!

I wouldnt block a BOV, thats just useless, pull it out or get a Greddy Type S!

Cheers

[R33vit]

Matty

3" turbo back

POD + CAP

Cam gear

FMIC

Autospeed boost controller

PFC

and a good 60 foot time.

[R33vit]

Oh

forgot to mention, it has a stock BOV because unlike the full time race cars, I dont strip and rebuild my engines every few meets, nor do I use a sequential gear box where you dont lift off the throttle...

[doridori32]

Oh

forgot to mention, it has a stock BOV because unlike the full time race cars, I dont strip and rebuild my engines every few meets, nor do I use a sequential gear box where you dont lift off the throttle...

Just get over it... ive done all the test's possible and dont use sequential boxes.

25+psi, no problems.. your car must be setup shockingly and using a plug-in power FC!

ohhh poor kid.

Petar.

[R33vit]

LOL

dad pass the landing net, I got a real one

[doridori32]

Sydneykid i would like to tell you your wrong.... very very wrong.

My Engineer told me to tell you that you don't know nothing and suck balls.

If you want his email let me know!

Im not being a smart ass but just giving you some real fact's. Stating BOV"s are useless pieces of shit.

Some Quotes...

PostPosted: Tue Jan 04, 2005 8:12 pm Post subject: Reply with quote

Tell us what you really think Pete, you always do. Laughing I think you would convince a lot more people if you specifically responded to the allegations, not just pay someone out Laughing

As explained ages ago (and re-quoted a few times), BOVs serve two functions in factory cars: (1) mask flutter noise; (2) recirculate air to avoid overfuelling in AFM engines. (2) is moot anyway because if you have deceleration fuel cut, you don't need to trick the AFM. (1) is the single biggest reason. Imagine your average joe driving this brand new series 6 RX-7 off the factory floor with the flutter noise every gear change. He would be straight back to the Mazda dealership asking if he has piston slip or has done a head gasket. Laughing

Service intervals increase because manufacturing techniques have improved. Are the failures your engineer friend speaks about the shaft snapping or the comp wheel shearing off? Because if what people are saying about BOVs is true then this is the kind of catastrophic damage you would expect. Those old nissans develop turbo oil seal leaks. This is not necessarily consistent with the allegations made about BOVs. Improved seal life is more consistent with the introduction of synthetic oils IMO, than it is the introduction of BOVs.

If what your friend is alleging about BOVs is true, they would not last 60,000km.

The sound is not caused by 'vibrations at the turbine blades'. The turbine blades are on the exhaust side, first of all, and second of all, there is no evidence that these vibrations are sufficient to cause any damage. You don't need much vibration to get fan blades to chop up sound. Tell him to go to his electric cooling fan in his house and yell into it. The sounds chops up. Now see if the fan comes loose and starts spinning around the room because he yelled into it. Confused go put your 500W subwoofer in front of the fan and it still won't ruin it. Not a valid comparison considering the speed at which the blades are turning, but still worthwhile considering the material a turbo is made of and the much smaller diameter of the wheel.

Once again, he, like everyone else who is pro-BOV, has completely neglected what is happening on the other side of the turbo. When you take your foot off the throttle, whether or not you have a BOV, the turbine will slow down simply because it longer has the strong pulses to keep it spinning at that speed. Why does this sudden slowing down not also ruin a turbo when running a BOV? The pressure on the exhaust side would drop rapidly so the resistance to motion on the side of the turbo must also decrease. Any sudden decrease in speed on the comp side is met with less resistance on the exhaust side, so the stresses (if any) on the turbo is far less than what is being claimed.

If no BOV does cause damage, it cannot be due to the turbo rapidly slowing down. It must be due to 'something else', no explanation of which has satisfied me so far.

:wassup:

[Roy]

LOL...do you realise your speaking to a bunch of engineers:)

Not being a smart a55, just curious to hear more thoughts:)

Ask you engineer friend about the kinetic energy of the shaft. Sure the exhaust pulses slow but they still act on the turbine, meaning that the turbine shaft will begin to slow mainly due to friction of the bearings.

So with throtte shut, lets just say the only think keeping the shaft/turbine spinning is its Kinetic Energy or stored energy. Now on the compressor side of things its obviously rotating at the same rpm as the turbine, common shaft and all.

So what happens when a pump (thats all a compressor is, just that it uses exhaust air instead of a 240V motor) tries to pressurise a fixed volume. Without a load beign applied to the turbine from the exhaust gases the shaft will want to slow as it will not have the required energy to keep spinning whilst trying to pressureise a fixed volume with the throttle body closed.

But this assumes the the compressor has a tight seal to the housing, which it doesnt...and air can easily flow back thru the compressor. The compressor on our cars are high flow low pressure units so ask them to squeeze air into a fixed volume adn they will struggle, tell them to flow air and they shine.

Another thing which may influence reliability is also the axial loads on bearings. The compressor will naturally want to sit back against the backing plate when there is a sudden increase in pressure in the housing. Its yet another load on the turbo bearing, in a direction they arent designed for.

So basically ramble thats off topic, but im bored and sick at home:)

I see your in Melb, take my little 2.0L Skyline for a drive with and without the BOV, trust me you will notice the difference. Perhaps its a little more evident when the turbo sizing is on the little too large side, if the turbo had a smaller compressor / turbine perhaps the things spools so quickly that it takes jack sh1t flow to accelerate the thing...

So many variables...but theory is typically right, and even when in some cases it may not eventuate in the real world, doesnt mean its wrong, just in that particular application its negligible

[C_DawG]

Sierra Cosworth's pushing 45+psi down mount panarama screaming with there external wastegate's and did NO damage.

No damage huh?

They changed turbos between every meet for fun?

[R31 POWER]

Yeh mate thats the THEORY, where is the prac like everyone else has to prove they dont do anything.

RACE CARS DONT USE BOV's!

FACTORY CARS DO FOR EMMISIONS!!!

I wouldnt block a BOV, thats just useless, pull it out or get a Greddy Type S!

Cheers

I don't normally post in threads that have turned into a shit fight in them but meh why not.

What race cars are we talking about? I guess the ones that don't are taking the "Keep It Simple Stupid" approach,one less thing to go wrong.

As stated before and is widely known that if you change gears very quick the BOV does'nt have time to open.So how quick do race car drivers change gears? I bet not slow so no need for one then.

And emmisions you keep saying,surely uncombusted air has no danger to the atmosphere in anyway.I know the oil vapours would be mixed in that air but I don't see it being that bad and if there's to much oil well then you have a prob.I know what air I would rather breathe from a automobile and it would'nt be from the exhaust.

And as for the Greddy BOV the thread on top allows you to limit the amount of travel of the valve inside the BOV.So screwing it right in stops the slide all together thus keeping it closed.

[doridori32]

No damage huh?

They changed turbos between every meet for fun?

Yes no damage.

That one 24 hour race on 45+psi would stress the entire turbo/engine/drivetrain more then your cefiro would in its lifetime.

[C_DawG]

Yes no damage.

That one 24 hour race on 45+psi would stress the entire turbo/engine/drivetrain more then your cefiro would in its lifetime.

Probably so.

Why has the Gibson GTR got a bit fat shiny orange BoV then? Track Rice?