Blow Off Valve Needed?

[_8OO5TED_]

I am about to fit a ball bearing GT30R turbo with all associated bits to my RB25 and am organising the custom intercooler piping too. I was considering running no BOV in the set up, just a clean run of stainless steel cooler piping. Are there any major problems with doing this? In other words, would it be wise to factor a BOV into the set up?

thanks.

[Craved]

try and run it to replicate the std setup, no stalling no risk of reversion causing damage

[R31Nismoid]

^^ and further to the wise man, use GTR BOV's.

The stocker probably wont last long with that sorta boost levels...

$150 for them, quite cheap really.

[Faid]

yes the standard item is surprisingly strong, i still use them after the advice Nismoid gave me. and i ram 24psi of bost using a T04Z. and when they do go off its like a tornado blowing, quite effective little buggers.

[Abo Bob]

So do GTR BOV's bolt straight up to RB25's? Are R34 and R33 RB25 bov's the same?

[MBS206]

No need for one IMO.

If porsche don't bother to run one on this http://www.youtube.com/watch?v=5LtkSCaE0EM then why bother.

Plus:

Every International Group C sports car to 1991 NO BOV

Every F1 car from 1979 to 1988 NO BOV

Every Indy car from 1970 to NOW NO BOV

DJR Group A Sierra till its last races NO BOV

And out there, in the great wide world, Nissan claim to only run the BOV, to reduce noise. (Flutter is louder then plumb back BOV)

Plus, hey, CA18DET, no BOV.

Remember, car manuafacturers build there cars to LAST a LONG time, and pass noise/pollution restrictions.

Think about, a company like Porsche, would run a BOV IF it could damage the compressor. And hey, even Nissan don't run them on the CA18DET...

[The Mafia]

haha my stocker is running with 18psi of boost on a GT30r and its still going strong.

[R31Nismoid]

No need for one IMO.

If porsche don't bother to run one on this http://www.youtube.com/watch?v=5LtkSCaE0EM then why bother.

Plus:

Every International Group C sports car to 1991 NO BOV

Every F1 car from 1979 to 1988 NO BOV

Every Indy car from 1970 to NOW NO BOV

DJR Group A Sierra till its last races NO BOV

And out there, in the great wide world, Nissan claim to only run the BOV, to reduce noise. (Flutter is louder then plumb back BOV)

Plus, hey, CA18DET, no BOV.

Remember, car manuafacturers build there cars to LAST a LONG time, and pass noise/pollution restrictions.

Think about, a company like Porsche, would run a BOV IF it could damage the compressor. And hey, even Nissan don't run them on the CA18DET...

Got an example that isnt a race car?

And a design that wasnt revisited and a BOV installed on its replacement motor?

HR31's didnt have a BOV either, but the R32 sure got one with its replacement motor aswell (just like the SR)

Either way, i'd use one. Arguments for and against are covered time and time over so use a search.

I believe a single GTR BOV's is a direct replacement in the stocker possie.

I ran a single GTR BOV on my setup without issue

[MBS206]

If you have a look at the motors that have had them put on them, you will notice, that they got fitted at the factory, when new/tighter noise and pollution restrictions came out.

Nissan say so themselves, that they used them to muffle sound.

And race engines enter ALOT harsher conditions on the track. Just a couple of hours out on a race track, in a full race condition, is years worth of abuse on a road car.

[R31Nismoid]

If you have a look at the motors that have had them put on them, you will notice, that they got fitted at the factory, when new/tighter noise and pollution restrictions came out.

Nissan say so themselves, that they used them to muffle sound.

And race engines enter ALOT harsher conditions on the track. Just a couple of hours out on a race track, in a full race condition, is years worth of abuse on a road car.

Yes, and hence, you should have one on there to comply with EPA rulings.

He is WA, so he is luckier than some other states in that respect, but in Vic, its a fair pain in the A.

As for the race motors again... why do most race teams rebuild turbos after each race? Surely one race isnt enough to kill something... heaven forbid

I guess its the same reason they change brake rotors and everything else, they dont want something thats potentially/is/going to be shagged/fatigued costing them a race.

There is a lot more to them just doing laps as im sure you are aware. So for something thats replaced so often, its not really a viable "lasting" test.

So IMO not a good example at all, but i do love it coming up though

[MBS206]

IMO, it's a very good example.

24 hours straight, going continously around a race track. In race conditions, that has to be more of a test the joe blow driving averagely, and occasionally giving it a hit every now and then yes?

They actually see full boost basically everytime the throttle is touched (unless feathering in corners etc) so each time they back down for a corner, all of that high boost is being jammed back through the turbo.

IMO, that is a MUCH harder and harsher feat, then just "average" driving on the road.

Looking to see if there's any newly released cars, not running BOV.

Also, as for the motors that had BOV put on them after being revised, have you yet heard of a shaft snapping, or fins bending/breaking, due to "no bov"?

[R31Nismoid]

Im not talking about turbo failure due to compressor surge, or race applications and the many different facets that encapsulate it because quite frankly i cbf'd getting into another compressor surge discussion as its about as productive as a dog chasing its tail.

im just stating, car comes with one for emissions, leave it on there.

some people have idle/stalling issues, some dont which is dependant on driving style it seems.

[FORZA-MOTORSPORT]

Intersting, im gonna test not running a bov on my rb30, having to build boost back up after changing gears seems like a huge waste to me

[Abo Bob]

Yeah the stalling compressor wheel is what does it for me too.

[Resin]

My car (cefiro a31 didnt come with bov) marketed as a family car

skyline r32 did - sportier car

[BOOSTD]

I run an ARC twin entry intercooler kit on my GTR(same as the mines one) The kit comes with plugs tp block off the BOV's. The car runs 370-380rwkw and 22psi. The combination of this cooler and blanking my BOV's resulted in 25kw extra mid-range. I don't know how much is associated to the cooler or lack of BOV's, however the bleed hole that recirculates air(whilst the BOV is closed) can only delay spoolup.

Edited November 1, 2006 by BOOSTD

[discopotato03]

This one seems to do the rounds so I'll throw in my 2 cents .

I know exactly how 80's era production turbo engines feel because I lived with a bog stock (catback aside) DR30 FJ20ET for a couple of years . These did not have the throttle closed recirculation valve .

It used to do weird things on a trailing throttle after running in boost at lowish engine speeds . You could back off the accelerator and on over run you'd get a bit of engine braking followed by a kind of mild surge probably caused by the volume of pressurised air between the compressor and the plenum not letting manifold pressure drop as quickly as desired . If it had been fitted with the manifold vacum operated throttle bypass valve air in the system could do the roundies (from compressor through the valves by pass plumbing back to the inlet side of the compressor but down stream of the air flow meter) . This means the compressor has somewhere to send positive pressure and recover this air but on its inlet side . Apart from the fact that presurised air is not trying to overwhelm the plenum in the throttle plate/s closing phase , the air flow metre is out of the loop ie not measuring much flow so the computer is not telling the injectors to inject fuel thats not needed .

My personal belief is that manufacturers fit this bypass recirc valve for three reasons .

1) Emissions - blind Freddy can see filthy rich overrun mixtures serve no useful purpose .

2) Drivability - when you close the throttle/s you want the engine to back off cleanly , not dilly dally .

3) Noise - Manufacturers have no interest in the bionic Baygon can effects of atmo BOV's/comp chatter

There are very good reasons for having the Factory or better systems in road cars . Sharp predictable throttle response is important as is good mixture control .

Race cars are a very differend breed and lowish speed antics are less of a problem because its not where they are in the heat of battle . For them compressor stall can be a problem though modern turbocharger systems are a far cry from the RS500 Sierras - which were a dogs breakfast in reality . Its getting off track but the homologated TA34 turbo was layed back heaps along the leading edges of the compressor blades to help stop them bending under rapid transients and high boost pressure . A turbo like a GT3076R would have made all the diference .

In a nutshell you have nothing to gain by removing the recirc system . If anyone wants a quick back to back remove the vacum hose (plug the hose too) and go for a quick spin . Don't blame me if you damage something by disabling a devise designed to prevent real issues though .

Cheers A

[BOOSTD]

This one seems to do the rounds so I'll throw in my 2 cents .

In a nutshell you have nothing to gain by removing the recirc system . If anyone wants a quick back to back remove the vacum hose (plug the hose too) and go for a quick spin . Don't blame me if you damage something by disabling a devise designed to prevent real issues though .

Cheers A

Removing the vacum hose causes the BOV to leak boost-at about 13psi as there is no positive pressure behind the actuator to stop the spring being overloaded. The onlyway to properly test is to fully blank the return or inlet

off. As for drivablilty on throttle back off the injectors are off, you can see on the PFC handcontroller they will state 0%, until the idle control cct is operational and enrichment problems with atmospheric BOV's arrise.

Having said all that, the noise from compressor surge will definately reflect increased bearing wear and shaft movement which is not a positive. I personaly don't run BOV'S as I have found a definate perfomance improvement, and I trust Mine's product. I am expecting premature turbo failure however the trade-off is worth it. The biggest difference is in part throttle to full throttle response, this is the stage were the pressure behind the BOV is less causing leakage. You will find a noticable difference in boost levels at part throttle with the BOV blocked off. I'm sure many can here there's "blowing off" at part throttle then closing at full.

Edited November 1, 2006 by BOOSTD

[West]

^^ and further to the wise man, use GTR BOV's.

The stocker probably wont last long with that sorta boost levels...

$150 for them, quite cheap really.

$150 for stock gtr bov, where do you get them man? Could have tell me earlier.

[MBS206]

I have pulled my line off the BOV, took it for a spin, it drive identical, just a lot more noise.

As for what R31 said, I'd actually have to agree, it's there for an emmisions reason (Noise) so leave it on if you're scared of the legalities.

Also, the compressor doesn't actually slow down, except for the fact that the wastegate stays open. The fins on a turbo, are UNIdirectional, not BIdirectional, meaning a force can only be applied one way... If you spin it backwards, it will not suck air through. Don't beleive me, go try it...

Whilst the turbo is spinning, it's unidirectional blades are still actually turning. Trying to push air intowards the engine. But alas, it has no where to go, as you just blocked it's path.

Now the air DOES create a fair bit of pressure.

Pressure is equal to force, multiplied over the area. Once this force becomes great enough, (larger then the force of incoming air) it flows backwards.

Once this pressure on the engine side of the turbo, becomes greater, then that on the atmosphere side, it flows "back" out of the turbo.

Since when the force becomes greater in the small space, it heads backwards, hence positive pressure coming OUT of turbo back towards air filter. But WHAM Physics works f'ucking quick, and the air pressure is now less, so BANG the turbo is forcing air back in TOWARDS the engine, creating a vacuum in the intake heading towards the air filter. So now we have a positive pressure pulse, chased by a negative pressure pulse. And this happens EXTREMELY quickly, until the turbo actually slows down because the exhaust gasses have dropped off dramatically (Hence the SLOWING of the turbo).

Hence, we have flutter from positive and negative pulses of air.

Okay, that isn't worded the best... So if you don't understand, just ask, I'll rewrite it. I'm slightly tired, and copied it from another reply I made on another forum about why the compressor doesn't actually "stall"

But the reason why the compressor slows down, is wastegate is still open, and exhaust gasses are being diverted away from turbo.