Gtr Bov

[Kaido_RR]

hey,

i was just wondering will running 1 gtr bov be ok for application of boost around 16psi with about 350rwhp to 400rwhp?

or will i need both of them.

and will i see any boost leak from them?

thanks michael

[R31Nismoid]

I ran 1 GTR BOV for over 330rwkw/24psi

[Kaido_RR]

awsome thats the answer im looking for thanks nismoid

[RB30-POWER]

If the factory GTR needed two BOV with only 206kw @ fly (bit more in reality, i know )

Surely a car that has close to 300kw at the tyres is going to benefit from having both.

[R31Nismoid]

Benefit how?

[RB30-POWER]

There is going to be alot more volume of air in the pipework at higher power levels then standard. Having both is going to allow alot more air to be bypassed back to the front of the turbos because only one is probably going to be to restrictive especially when you snap the throttle closed on big boost and still cause some reversion through the AFM and turbo's.

Did Nissan put two on for no reason, just to waste some money?

Im not trying to be smart, just asking?

[R31Nismoid]

Im not sure why they did either... and i dont know

I just see it as... If it worked fine for me with one, no flutter at all... then it must have been letting all the air out through the single one

Maybe it has something to do with the two turbos and the recirc @ idle or something?

[GTRgeoff]

The volume of the air recirculated will be the key. Unfortunately you never got to run the car on the circuit Ash or you would have discovered the benefits of running both.

The reason it didn't flutter is because the was always pressure against the throttle butterfly because it wasn't releasing all the pressure. The flutter is caused by the valve opening and closing as controlled by positive pressure at the butterfly.

[R31Nismoid]

What do you mean it wasnt releasing all of it?

Can you explain differently... you've for once totally lost me

[GTRgeoff]

No worries mate, I'll go a bit long on this one for other readers.

Air has mass, so as well as having static or guage (Boost) pressure it has momentum or velocity pressure. Consider a really big pressure vessel where the air is sitting still. If the compressor were operating in there at atmo pressure then you instantly change the pressure to one bar there would be little difference in what was going on with the compresor. It would just be stirring the air around. It isn't the boost pressure that is being released by the BOV.

In the engine the air is moving from one place to another at a high speed so has serious momentum. When the throttle body closes the air has to stop or go elsewhere, usually as a reversion wave like water hammer when you turn the tap off fast which goes back to hit the compressor which is slowed but then continues to try to force the air in so people without BOVS get their voop-voop-voop sound which is the compressor being hit by air impulses. Impulse energy is not good for any mechanical device and for a turbo would mean much increased loadings on the bearings and even seals as well as possible beyond fatigue limit loading of the shaft meaning it could snap off after a few thousand of these impulses.

When a BOV opens it releases the air momentum to allow the compressor to continue spinning. Because air has momentum it also aids in dragging air through the compressor without the aid of the turbine forcing it along so reduces the drag keeping the rotating velocity high so potential energy is there to bring boost back on faster. Much like a helicopter pilot who loses engine power can wind off pitch on the main rotor and dive to maintain rotor speed so he can pull pitch at the right time to do an auto-rotation landing.

When you have a too small capacity BOV the air will continue to escape in a continuous rushing sound. If it is way too small you will get some reversion noises. A large one, depending on sensitivity will either open and close rapidly (very sensitive) or make a single release sound which will reduce in intesity untill equalising but still giving a slight flutter.

I ran 2 on the race car. One for road (stock) which was too small for even 220rwkw with large average power which just hissed contiuously off throttle and a HKS atmo which had plenty of capacity. It gave just a squeak on in gate changes since those shifts are pretty quick, but on cross gate changes like 2-3 and especially 4-5 it could be heard working and improved the time for boost to kick in after changing a lot. Individually the GTR bov's are not huge (I have a pair for after the rebuild on the racecar) but together simply act like a much larger one. I very much like the way they work in the GTR. They are probably adequate for street use at those levels you were running to prevent damage.

Let me know if that makes it clearer.

[CruiseLiner]

just offtopic a fraction but whats the going rate for a set of stock gtr bov's secondhand???

[RB240Dav]

Giving thought to the moving mass of air, does this imply that the location of the BOV's is just as important.

I have been contemplating moving the BOVs to the hot pipe, pipe between turbo and intercooler, to make plumbing easier on my custom rb26 setup.

It would seem that the BOVs would still relieve the air's momentum from hitting the compressor, but only after returning from bouncing off of the throttle bodies.

Would the only concern be the loss of the air's momentum in a single direction through the intercooler, and would this be enough of a concern not to go with this setup; once again, BOVs on the hot pipe for a much shorter recirc to the AFMs.

[RB30-POWER]

Well they typically say closer to the throttle body the better.

However i really don't think it would matter a hell of alot.

One functional problem i see having the BOV's before the IC (hot side) is if there is any pressure drop across the cooler, then the vacuum line that is plumbed to the back of the BOV diaphram will have less boost pressure from the plenum and may cause the BOV to open/leak.

The BOV relies on equal pressure on each side of the diaphram to keep it closed under boost.

EG, 6psi in plenum and 6psi in pipework just before throttlebody will keep it closed.

If you have a pressure drop of say 2psi across the cooler, you will have 6psi in the plenum but 8psi in the pipework (hot side), causing the BOV to potentially open, because the pressure isn't equal on each side of the BOV diaphram.

It will work if you don't have any pressure drop across the core or you have the springs real tight on the BOV. (Defeats BOV purpose then though)

Just something i though i would mention, alot of people sometimes miss the little things that can cause gremlins down the track.