Love the sound of a bov

But doing a little research found this article

 

Any truth, I can understand logic behind what is said but quite often see them fitted

 

"Z32: Don’t install blow off valves on a 300ZX

 

Tech Article: Don’t Install a BOV on a 300ZX

Composed by:*300ZXttZman

By: Greg @ Specialty Z

 

Here’s why you won’t want to install BOV’s on a engine with a MAF sensor: When you make any positive boost and you close the throttle without a BOV or recirculation plumbing, the pressurized air will stop moving and stall the turbo.

 

Blow off valve:

What a BOV does is open a valve when you let off the throttle by way of engine vacuum, this allows the air to be released into the atmosphere. This is better for the turbo than nothing in the system because it allows to turbo to keep spinning.

 

The problem with a blow off valve in a MAF sensor set up is that because the turbo is still spinning, new air is being pulled into the turbo from the air filter and is being measured by the MAF sensor. So the ECU believes all the air coming into MAF is going into the engine that is now being pushed out into open air. So when you hear that sound of air rushing, the engine is pumping fuel in for all that air you hear coming out. This causes the engine to want to stall, because it is being flooded with fuel.

 

The engine wanting to die is one thing, the other is that all the unburned fuel going into the cylinders will not burn and this washes the lubrication off the cylinder walls and the engine rings, creating premature engine wear.

 

The plumbing on a Z with MAF’s is not designed to work with a BOV and you can not tune it out. A MAF measures the air being drawn past the air filter to allow the ECU to calculate the fuel needed. The MAF needs to be measuring the air and the ECU has no way of knowing when you’re blowing some of the air outside the engine.

 

What a MAP sensor does is measure vacuum and pressure in the intake manifold to tell the engine management how much fuel is needed. So it does not matter what happens in the pipes before the throttle body with a MAP system, as the MAP only measures what happens in the engine and not what is happening BEFORE the manifold. BOV’s work fine on MAP set ups, but a recirc valve is always better, as it is helping to keep the turbo spinning by feeding the turbo air.

 

Recirculation Valve:

The stock Nissan recirc valve is larger than most aftermarket BOV’s. The stock Nissan BOV is also stronger than most aftermarket BOV’s. The stock recirc’s can handle more than 40 PSI boost pressure. What a recirc valve does is similar to a BOV, but better. Just like a BOV the recirc valve opens when it gets a vacuum signal – the difference is that instead of allowing the air to be blown off into the atmosphere, the recirc valve blows the air back into the front side of the turbo.

 

What this does is let the air out from the pressure side of the turbo and blows that air back into the suction side of the turbo. The air pushing back into the front side of the turbo is helping it keep spinning because it is recirculating the air. The air simply goes out of the turbo and right back in.

Because the air that is coming out of the turbo is going right back into the turbo, no new air is being pulled in through the MAF because the air is going in a loop.

 

Removing the stock recirc makes zero sense and will only cause issues with stalling and filling your crankcase with fuel. As long as you run a MAF you should never install a BOV.

 

Now, the reason some BOV’s cause less problems is that they come with different springs, a heavier spring requires more vacuum to open the valve. The problem with too stiff of a spring, is the valve is not opening enough, this will cause compressor surge and is hard on the turbos."

I'm hoping he's going to say stock or 99, I never like the storesk one it had personally, it's my second least favourite over the basking shark.

 

well its a tose up over the 99 spec but i really love the twin z p spec its absolutly lovely but i live around loads of speed ramps. if i could afford air this year but i cant it would be a no branner.

you cant say this is ugly it the tits and with a fat rear i think it would finish the car of lovely,

and sorry i dont want to sabatarge this thread,so no more.

I really don't like the TwinZ front bumper AT ALL. It's one of the only things they make that I don't like as all their other stuff looks fantastic. That bumper makes it look like a Dust Buster....or a basking shark!

the twinz bumper kicks arse I like it am in to minds to use one and sell the 99 spec bumper I already have I just don't know

the twinz bumper kicks arse I like it am in to minds to use one and sell the 99 spec bumper I already have I just don't know

 

stick with my 99 then job done

With regards to BOVs...

 

Generally speaking, standard 20+yr old recircs are only good to a point, as far as boost levels go, hence an aftermarket solution may be required, be it recirc or VTA which is easier to implement. Fitting them purely for the noise is different and down to personal preference, taking into account the possible issues on a MAF-based vehicle. A MAP sensor set up (standalone ECU or VPC) or simply having the MAF after the BOVs in the IC pipework eliminates any fuel delivery issues. Regardless, with a good-quality BOV set-up you will only get a tiny instance of overfuelling before the ECU cuts all injection events due to overrun (TPS closed, RPM>1500 when Temp>70°C; unless this has been mapped out for flames of course).

 

I personally don't run any type of dump valve on any car, regardless of boost level. Removing recircs altogether does not cause compressor surge of the damaging kind. On-boost surge is a different phenomenon altogether. As far as I'm aware there is nothing to suggest premature turbo failure, but a recirc set up does indeed reduce noise-pollution which is the main reason they were fitted, along with ribbed intake pipework, exhaust silencers etc.

 

When you make any positive boost and you close the throttle without a BOV or recirculation plumbing, the pressurized air will stop moving and stall the turbo.

What actually happens is the pressurized air flows back towards the compressor outlet and causes flow instability at the compressor itself. The fluttering noise you hear on lift-off is this flow interacting with the blades in a non-laminar manner. It is this scenario which, in engineering terms, is called compressor stall. When the terminology is applied to modified cars, it has been interpreted that the shaft actually stops spinning. This is untrue. Although there will be some additional stress, since the car is on overrun with the throttle closed, the turbine (exhaust) wheel isn't experiencing high applied torque and the flow subsequently stabilises (the fluttering stops).

 

Any BOV with a weak spring is going to cause running issues due to unmetered air. If you must run them, look for an SSQV-type unit or a good quality twin-piston with adjustable spring (I've had good results with GFB BOVs). Personally, I can't stand them as they're just another component that can fail. However, any "McDonalds/chav" hyperbole is pointless as it fails to address the actual facts of the matter whilst being mildly offensive to the many thousands of people running BOVs on MAF-equipped cars. Much worse than running a BOV, or even a Veilside bodykit :laugh:

 

From a noise perspective, I prefer a "flutter/chatter" over a "tish" any day of the week :)

I may well revert to your method Noel, for a few reasons really that I shan't litter the thread with. Your car makes just as many exciting noises as mine just differently.

Fitting them purely for the noise is different and down to personal preference...

... being mildly offensive to the many thousands of people running BOVs on MAF-equipped cars.

Many thousands of people wear socks with sandals - another fitment down to personal preference which also deserves as much opprobrium as it gets. Really beyond the pale, my dear.

BTW, "willy waving McDonalds car-park modification" isn't hyperbole. It isn't litotes or meiosis either. Might be a simile or possibly a metaphor. Where's Cato when you need him?

BOVs delenda est

Edited August 29, 201411 yr by Gio
Latin 0/10 chiz chiz

Many thousands of people wear socks with sandals - another fitment down to personal preference which also deserves as much opprobrium as it gets. Really beyond the pale, my dear.

BTW, "willy waving McDonalds car-park modification" isn't hyperbole. It isn't litotes or meiosis either. Might be a simile or possibly a metaphor. Where's Cato when you need him?

 

Not overly fussed about semantics or individual fashion choices I'm afraid, just the technical aspect of the topic in question. Well done though, that's some fancy linguistics you've done there. Got me beat without the use of Google, although the statement wasn't a simile. Have some internet points on me :laugh:

 

From a noise perspective, I prefer a "flutter/chatter" over a "tish" any day of the week :)

 

:bow:

Cheers guys

 

Over whelmed with response

 

I think I'll stick as is as done the plastic fantastic bit before

 

Pledged to no add bits that do no make it faster on this one!!!

:bow:

 

I have both waste gate chatter and BOV's

my zed didn't have them so I fitted them. thought it was cool for a couple of years then thought how gay do I sound, here I come what for it tissss yeah baby how good was that tissssss lol!!!!

 

then put it back to stock sooooooooo much more classy as the zed should be. its not a gt5 or rs turbo and there so dated the only thing there good for a scaring ****er cyclists that cycle 4 a breast :xxx:

 

- - - Updated - - -

 

my zed didn't have them so I fitted them. thought it was cool for a couple of years then thought how gay do I sound, here I come what for it tissss yeah baby how good was that tissssss lol!!!!

 

then put it back to stock sooooooooo much more classy as the zed should be. its not a gt5 or rs turbo and there so dated the only thing there good for a scaring ****er cyclists that cycle 4 a breast :xxx:

my new car has them fitted already so to eary for me to make a comment as ive not picked up car yet as im working tell next mounth so no comment from me

My most recent car had them and I was going to have them fitted to my new one but after what Noz has said and explained very well I am having second and third thoughts sorry to hijack thread a bit but seems there so many technically minded people posting on here can someone explain the benefits of external waste gates?.. and when and why would you fit or not?.

Slightly better spool and response, with the penalty of them being quite big and a sod to fit in our engine bays. Until you are in BIG after market turbo territory you don't get an option.

 

And for those who are uncertain, as I understand it. The wastegate is a pressure relief valve in the power generation hot side of the turbo. It diverts exhaust gas around the compressor wheel to stop the turbo running away up creating more and more boost. It is actuated by the wastegate actuator (the bit that looks like a bicycle bell on a stick.) often this bit is refered to as a wastegate. The bicycle bell bit is a sprung diaphragm with a boost feed in the top, once at the set boost, it does a game of mousetrap and pushes the rod to open the wastegate about 6 inches away inside the turbo.

 

An internal wastegate the actual relief valve is inside the snail of the turbo, an external wastegate diverts exhaust gasses around the entire turbo. The benefit is to the turbulance of the exhaust flow out the back of the power turbine.

 

to my understanding.

 

Edited August 31, 201411 yr by tomfromthenorth
added picture

Yup that's the wastegate there on the right, once the actuator sees the pressure required it pushes thus flap open, the excess gasses then pass through here limiting the speed the turbine is spinning. It's likeca diverter valve it literally wastes off the air. Very simple really.

So I was reading that fitting an external wastegate helps provide steady boost control at any pressure level and makes it easier to control and set a more precise and constant boost level thus helping with less lag throughout the range is this correct.

Yeah on a drag impreza with a boost level measured in Atmospheres!

so unless your upgrading to bigger turbo's and your internals its pretty pointless then yeh

As I understand, a large portion of the performance benefit is from the better aerodynamics in the turbo exhaust outlet. If you look at that picture above, gas leaves the turbine then enters a large chamber that houses the wastegate. The gasses will immediately expand and slow down, causing the gas following it that is travelling through the turbo to "run into a motorway pile up of slowing gas". Plus any mixing from the two sources if the wastegate is open, causing Eddie currents and what have you.

 

And you need to buy a turbo that doesn't have an internal wasegate, leaving you with a choice of big ones. I think an EBC will control and damp any boost oscillations perfectly well for normal application. Buy a top end EBC.

you know my birthday's coming up soon tom :) I'l have https://www.conceptzperformance.com/Cart/description.php?II=1108 lol

You can run internally-gated turbos with an external wastegate: You simply weld the wastegate shut.

Noz yeh i did read that somewhere what ws really after was if there would be a benefit using external waste gate with stock turbo's on a mildish tuned engine say running 430 450 ish

Oi! That's my saying! :wack:

 

I totally agree though. I've been saying that BOVs are useless tat for years, even before reading Greg's report into them on TwinTurbo.net. Back in the early 2000s, a mate of mine bought a Cavalier Turbo and fitted one against my suggestion. After having it fitted for a few months, he wasn't impressed with it and reverted back to the standard recirculating valve, he found that not only did it run better, but that responsiveness was also better.

 

As much as they are down to personal taste, they have plenty of negatives. Spunking out £220 on a pair something that does nothing just leaves me bereft. A willy waving McDonalds car-park modification if you will. :)

 

IMO, never has there been such a good case for something being so utterly pointless. :) Hell, not one single manufacturer the world over has fitted one to a production car, that probably tells you something. :rofl:

 

What he said.... :wink: