BOV - Do I need one ?

[B-Man]

Yo, me again,

Been thinkin about BOV's - If I have a Steel exhaust turbine (new turbo), FMIC and 3" pipes all the way round the FMIC, do I really need a BOV ??

The turbo could hack it, and think of all that pressure I am venting when it could be going into the engine......

The noise is cool, but I could do without the attention .... plumbing back is another option...

Looking for your 0.2c

Cheers,

[Silver-Arrowz]

How much boost you running? Also how much boost can standard BOV withstand? Just helping you out.

[B-Man]

Silver, thanks dude !! 14 PSI low, 18 PSI high - but it's not the BOV that I'm worried about - it's the turbo....The BOV is a Turbosmart Supersonic, so it can handle it.... Just wondering if I really need it...... Turbo life, etc.....

Cheers,

[Steve]

Brendanf - have you ever heard what it sounds like when the pressure from you pipesand coola is reversed and hits the compressor wheel? pft, pft pft, pft - It doesnt sound pretty.

The plumback could be an option, but I think any BOV if fitted and adjusted properly is a worthwhile thing to have as they stop the back pressure slowing down the urbo on gear change - once slowed they have to speed back up again = lag. Sure the lag wont be as bad if you are going hard, ie less time between shut/open throttle valve and because you have the foot to the floor, but that air must go somewhere and that is straight back through the turbo the wrong way.

I probably need to duck for cover here, as I know that there are a few lads out there that seem to think that a BOV is a complete waste of time and money, but, as requested,

This is just my 0.02

Steve

[B-Man]

Steve, thanks man - no I haven't heard that - But I can imagine the stress.. Which is why I asked the question ...... It really comes down to physics - I know the BOV is the safe option - And I don't wnat to open up a shit fight - I'm looking for ppls opinions and experiences, so I can make a decision.

Right now, I am gonna plumb the BOV back to the air filter - but if there is a compelling reason to do without it altogether, I'll listen to that too !

CHeers,

[Blitz]

Brendan,

have a chat to Merli, He fitted the Trust Type R, one of the best BOVS on the market for heavy duty applications such as yours.

If you need one pm me as we have to in stock at UAS that are available at a very good price for you

[Tosh]

Considering all of the back pressure forcing your Turbo to spin the wrong way, my opinion is that a BOV is essential. And considering what you've just done to your engine, I would imagine the last thing you'de want is shortened turbo life. For a BOV to be cleared legally, you do need it plumbed back into your intake.

and think of all that pressure I am venting when it could be going into the engine......  

If you plumb it back into your intake, then you're not going to be wasting it at all

As it is on my car from the factory (albeit an MR2), my BOV is plumbed back into the intake pipe between the AFM and turbo inlet.

My $0.02 and happy decision making

[Merli]

Originally posted by brendanf

The turbo could hack it, and think of all that pressure I am venting when it could be going into the engine....

Hey Brendan...

Okay, your theory here is quite flawed. All that air that's being vented wouldn't be going into the engine, because the BOV should only open when you've shut your throttle body, and not letting any more air into the engine anyway!!!

Does that makes sense? Basically your BOV should just be lying dormant until such time that you take your foot off the accelerator. Your throttle body shuts, but your turbo is still spinning VERY quickly and trying to force air past your now shut throttle body. Where can that air go?

Well if you had a BOV, it would vent to atmosphere, or with a plumbback, it would be returned into your intake manifold, before your turbo which means air will flow back through the turbo in the right direction.

If you didn't have a BOV, where would all that rushing, pressurised air go? It ain't going into your engine as you think, because the throttle body ain't letting any air enter... It's going to have to STOP, turn around and travel back through all your piping, back through the intercooler, and try and force it's way back through the turbo, causing what's called "REVERSION" of the turbo blades... This wall of compressed air going backwards hits the turbo blades like a shockwave, and is NOT good for the life of the turbo.

When I bought my car, it didn't have a BOV on it, and I quickly threw on a Blitz Dual Drive that I had... It wasn't big enough for my application, and it caused my car to run like crap... The spring wasn't strong enough and it wasn't completely shutting and leaking air... So I got rid of it, and put a Trust Type-R on there, as BY BY said, and the car runs PERFECTLY. Even though it vents to atmosphere, the Type-R has a super strong spring that shuts the BOV TIGHT, and doesn't allow any air leak, even at high boost pressures.

With your car, I'd probably suggest the same BOV.

Hope that helps dude.

[B-Man]

Thanks guys,

Yeah, I thought as much - And you are spot on Merli - I realised after posting that the air isn't going into the engine, it's being pressurised between the turbo and the throttlebody butterfly. I was told (prolly unreliably) that with a FMIC and steel zorst turbine that even with the pressure, it should be OK , and when you go to open throttle again, you have boost imediately (rather than having no pressure between TB & Turbo and boost would need to spool up again.

I may just plumb the Turbosmart Supersonic back in (ATM vents to atmosphere and makes a filthy sound) - I'll talk to you guys about the trust jobby tonight...

No BOV is def. bad idea.....

Thanks fellas,

[Roy]

About blow off valves opening under boost, that shouldnt be happening if the thing is on good order.

On one side of the diaphragm you have the compressed air from the turbo, the other side you have air from the inlet manifold. So under boost both sides of the diaphragm see the same pressure (Note: about the same pressure as your BOV is usually mounted close to the throttle body so only place for possible pressure drop is the throttle body itself)

so with combination of spring trying to resist being compressed, as well as both sides of the diaphragm seeing the same pressure, it should remain sealed and not leak boost.

Now when you back off the loud pedal and the throttle body is closed, the compressed air from the turbo is now increasing as it is attempting to pressurise a fixed volume, also the inlet manifold is now in vacuum.

So the diaphragm of the BOV now has increasing pressure on one side and vacuum on the other, so resulting in the valve opening. This vacuum and pressure from the inlet manifold is the reason you dont need stiff springs, as the pressures are acting as a means of sealing/opening the valve.

So there are plenty of BOVs due to their age and quality, that leak. This has mostly to do with the quality of the seats (or the internal surface of the valve that meets when closed)

On any turbo car i think they are a good idea, in fact necessary. In addition to the reasons mentioned above there is also a fluid property of air called Adiabatic combustion, meaning that when it is compressed it heats up. So by making the turbo further pressurise the air in front of your closed throttle body, you are further increasing the temperature of the air. By venting it to atmosphere you avoid this, as well as plumbing it back to behind the filter to be compressed and coled again.

Now if only someone can tell me the type of BOV being used by the yellow S14 on Best Motoring 6, im off to buy one. It sounds great. For that matter so doues the White Amuse Supra in Best Motoring 5.