Aftermarket BOV, performance or wank factor

[hypntk]

Simple question, do aftermarket BOV actually improve performance or do they just make a cool sound :whackit: Are they better than the stock ones at reducing lag or do they do the same job just soundin better?? I ask cause a few ppl ive talked to think they just sound cool and some ppl have told me they actually reduce performance cause they let more air out to get the sound and thus it takes more spool time once the clutch is let out again?

[Guest Mashrock]

hmm depends i guess, i still have the std ones on my car and they are very loud still. and still do their job very very well.

i'd think that a plumb back system would be the best being aftermarked valves or std ones.. and legal.

but i'd think that the atmo ones are just a bit of wank value.

[Wazz]

wank wank wank

[elbee111]

OK. Old fart talking now.

I always thought that a BOV was just wank wank.

My wife talked me into one (actually had it installed before I knew about it).

Well I am now convinced. It seems to be smoother/quicker on gear change (might be something to do with not putting back pressure on the turbo ??)

Anyway, I am happy with it. Especially because it is a GFB stealth and I can turn it down (it is adjustable for both pressure and plumb back ratios).

Enjoy!

El Bee

[NZM.031]

it depends on what you are doing. my car is a drifter, i have a HKS ssqv plumbed back in. it doesnt make much noise, just flutters. i used to have to to atmosphere, and i did notice a difference in on-off-on throttle response. im going to get new i/c piping made and will be removing the BOV all together as the car is either parked up, or sitting on rev limiter, very rarely driven.

i used to think they were cool and served a big purpose....but im over it now. ive never seen or heard of a turbo being damaged from reversion.

but an aftermarket one is better than most stock ones as they leak after a while, except for GTR bovs, they are exceptional.

cheers

Linton

[runn3r]

Simple question, do aftermarket BOV actually improve performance or do they just make a cool sound  :whackit: Are they better than the stock ones at reducing lag or do they do the same job just soundin better?? I ask cause a few ppl ive talked to think they just sound cool and some ppl have told me they actually reduce performance cause they let more air out to get the sound and thus it takes more spool time once the clutch is let out again?

On turbocharged vehicles, Blow Off Valves release excessive boost pressure trapped inside the intake pipe when the throttle is released. This release of pressure is important because as the vehicle accelerates, the turbo builds a high pressure air stream through the throttle body and into the motor. When the driver lets off of the accelerator and closes the throttle plate, the trapped air instantaneously has nowhere to go. This trapped air begins to travel back towards the turbine blade causing excessive strain on the blades. Prolonged exposure to these conditions can cause premature turbine wear and eventually cause turbine failure. The Blow Off is designed to effectively release this pressure into the atmosphere though but well cops will be running after yea. Do get it done on a none atmo. Hope this helps.

[Steve]

I used to think a bov was essential, until I removed it all together. It was explained to me that for on/off throttle response, depressurising the intercooler and pipework was a bad thing. Not just for drift, but also a spirited driving where you might adjust the throttle slightly - as soon as you back off even slightly, the bov lifts and you have throttle lag.

Much, much better throttle response once it was gone, the car feels quicker without it, and is better to drive IMO.

As for damage to turbo, hmm, not sure exactly how it is supposed to damage the turbo, certainly dont know anyone who has had turbo failure that could be directly attributed to no BOV - I have heard arguements for and against on this one, such as the sound you hear is the air going around the compressor, not jsut slamming up against it, which makes sense to me.

Does anybody have any hard evidence either way on this? or is it just one of those 'accepted things' that has never been tested or proven?

[gtrGhosTDoGG11]

I remember a interview was done with the Vielside boss. He commented that his drag cars did not have BOVS to save weight and maybe more power like steve suggestged. He also commented that his turbo's had to be replaced more often because of this, but I guess he doesnt care about that does he, as he can shit turbo's out of his arse.

[Steve]

any more details? what sort of boost? did he say how much shorter the life was? I wonder if a big boost drag car would have the same issues as a mildly tuned street car?

[Rolls]

Ok heres my thought. If the reversion of the air coming back out the intake (flutter sound) could cause any damage to the turbo surely it would bend the butterfly first. I mean Im sure the metal plate that is the butterfly would be much weaker then strengthened turbine wheels. Alot of cars didn't come with blow off valves at all, eg my stock R31 turbo passage was brought out with no bov at all, not even a plumb back so it makes a cool flutter. The reason alot of cars have plumback ones is to reduce the flutter sound which makes alot of people go "wtf is that"

At least thats what I think.

[FATGTS-R]

I dont think the theory is that it will break the compressor wheels or bend them its more to do with them spinning in one direction and the air coming back against it placing stress ( how much who knows? ) on the complete rotating assembly, bearings etc.

I also have an import R31 which came with no BOV at all but I fitted a Bosch unit because in theory I beleive having none at all cant be good.

I need to upgrade it now as I have increased boost pressure, hence airflow to the point where it cant vent it all and I get a small amount of flutter as some of it goes past the bov and through the turbo.

[Angry]

mine too came withouta bov...... car was stock as a rock .. for 16years of its life ..(till i got it that is) ....std turbo now runs 11psi and a HKS SSQ....but still has slight reversion on low boost... ..... althought it still auto trans at the moment......its kinda wank wank..until its manualed.

i didnt notice much of a difference between ..the lack of bov and ith it installed.. with both std intercooler and now fmic...... the psh is louder with more boost thats about all ..

for mild street use a bov is good thing ....but i think it comes down to drivers personal discretion.

Matt

[Sydneykid]

Some of my previous posts on BOV's;

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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 anyone 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 ............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?

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The idea of a BOV is to prevent the air from reversing direction when the throttle is closed. This has 2 effects;

1. It prevents the compressor being suddenly stopped (or run backwards) when the air rushes back the wrong way.

2. It keeps the air (in the intercooler and pipework) moving in the right direction ie; towards the engine.

So it would appear to me that #1 would be satisfied no matter where the BOV is located. But #2 is best satisfied by having the BOV as close to the throttle body as possible. That way none of the air is going the wrong way. This would mean better throttle response when the throttle is re-opened.

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So by not running a BOV or by excessivley tightening it, you are shortening the life of your turbo and you are decreasing the performance of your engine. It seems like a dumb idea to me.

If you want to know more, do a search, this subject has been discussed so many times:cheers:

[Steve]

Seems like a dumb idea to you, didnt really seem like a dumb idea to a jap guy I know who is a pro drifter (D1), qualified mechanic and owns his own mechanical workshop in Japan - he suggested it was the reason I was getting throttle lag, he doesnt run them for that reason - as alot of jap d1 drivers dont (yes some do).

As for why manufacturers run them, PLEASE dont tell me that manufactures do things purely for performance - perhaps NVH and emissions have more of a job to play?

To be objective in any comparison, you have to compare apples with apples, not turbo fitted to car type x to turbo fitted to car type y.

Lastly, who the hell said air reverting is good for the turbo? If you read the comments above, they are talking about performance - not lack of it as in a stock car to do the shopping in, so lets keep things on track.

As the title of the thread asks, is a BOV performance or wank factor??? note the use of the word 'performance'

please, dont be so ready to come down on those that have a different opinion than yours, if you have any realistic evidence please present it, but lets try and keep it objective so that others can make up their own minds too.

[inissane]

lol I went through all this crap b4 like many im sure, you just have to learn to move on from the bov crap and realise that turbos make power and torque, these little things are decoys eating ur money for no reward but a psshhh.........

I was going to get a greddy type s for $260, then I realised my foolishness and bought a RB25 garret turbocharger for $300 - id like to see a bov give 190rwkw!!!!!

[elbee111]

Well, the original title of the thread asks if "aftermarket" is performance or wank (versus standard I assume).

I always thought it was wank only, but am happy with the aftermarket now. Definately feels smoother and quicker in the changing up for mine.

As per my earlier post, I doubted it but am now convinced.

The original may have been faulty or somehow adjusted I don't know.

El Bee

[xRHETTx]

Personally i cant see how an aftermarket BOV could be any better than the stock one? Maybe with increased boost the standard spring pressure could be too close to the pressure in the inlet piping and therefore some leak could occur? Increasing the stiffness of the stock spring would be the easiest way to overcome this, and would be a hell of a lot cheaper to do than buying an aftermarket one.

On the BOV vs. no BOV argument, if the compressor blade is slowed or even starts spinning in the wrong direction, this would create a massive restriction in the turbine, reducing air flow out of the engine and therefore performance would be decreased.

Would it be possible to re-route the BOV air directly into the turbine? Would this act like some type of anti-lag device? Or is the pressure in the turbine more than that in the inlet piping when the throttle is closed?

[GTR-Ben]

Correct me if i'm wrong, but a lot of drag cars not running BOV's. Is this partially to do with them having such huge turbo's that there is a lot more clearance around the compressor, and air returning off throttle would not have as much effect?. That and they are on WOT for most of the time anyway.

[Steve]

On the BOV vs. no BOV argument, if the compressor blade is slowed or even starts spinning in the wrong direction, this would create a massive restriction in the turbine, reducing air flow out of the engine and therefore performance would be decreased.

Think you may have the wrong end of the stick there. You are absolutely correct that if you stopped or put a brake on the turbine wheel while you were ON THE THROTTLE, it would cause a few issues.

the bov debate refers to what happens when you are off the throttle, then back on.

Here is a quote from another forum that explains it differently:

As for the pressure build up slowing the compressor, bollocks. The loss of exhaust gas energy on closed throttle is many orders of magnitude greater than any energy the reflected pulse might impart to the compressor wheel. The wheel does slow on closed throttle but just because you have taken away the energy that drives it.

What most people don't understand about turbos is that they are NOT a pump, they are a turbine. All turbines do is speed up air. You create the pressure differential by that fast moving air hitting the diffuser and slowing down again...basically more fast air runs up the arse of the slowed air in front of it thereby creating a pressure increase. You can run a turbo flat out with your hand over the outlet and once you overcome the energy from the moving air boost pressure will stabilise and NOT continue to build...it'll just stop moving air. It's not like a positive displacement pump (roots blower) that will keep trying to force more air in.

Here's a classic test for the doubtful. Grab an electric fan (the turbine) block the outlet and see what happens.....you'll hear the fan actually speed up, NOT slow down.

and another

second part of the article actually went into the maths. Using the volume of air contained in the piping, the pressure, velocity and all of those variables, it was worked out that the amount of force imparted by air on the compressor wheel due to compressor surge at sudden throttle shutting was very neglegible. certainly not enough to ever damage one.

like I said before, there are arguements for and against. I would love to see specifics of what controlled testing has been done - otherwise its just speculation as to what EXACTLY is happening.

GTR-Ben, think you may be on the money - shift times would barely warrant any sort of bov - but its hard to say, dedicated drag cars dont always use intercoolers with turbos either.

[Sydneykid]

Seems like a dumb idea to you, didnt really seem like a dumb idea to a jap guy I know who is a pro drifter (D1), qualified mechanic and owns his own mechanical workshop in Japan - he suggested it was the reason I was getting throttle lag, he doesnt run them for that reason - as alot of jap d1 drivers dont (yes some do).

As for why manufacturers run them, PLEASE dont tell me that manufactures do things purely for performance - perhaps NVH and emissions have more of a job to play?  

To be objective in any comparison, you have to compare apples with apples, not turbo fitted to car type x to turbo fitted to car type y.

Lastly, who the hell said air reverting is good for the turbo?  If you read the comments above, they are talking about performance - not lack of it as in a stock car to do the shopping in, so lets keep things on track.

As the title of the thread asks, is a BOV performance or wank factor???  note the use of the word 'performance'

please, dont be so ready to come down on those that have a different opinion than yours, if you have any realistic evidence please present it, but lets try and keep it objective so that others can make up their own minds too.

Oooh goody, a healthy debate, it's been a bit boring around here lately.

I don't know about you but I don't want to be rebuilding my road car turbo as often as Jap D1's. As I said we do it on the race cars every 2,000k's, it's a pain in the ass and expensive. We used to do it on the Sierras 3 times in a race weekend, but they ran 2.5 bar and no BOV's. That's evidence.

I didn't claim Nissan put BOV's on their cars for performance, I believe they did it to improve turbo reliability. The increased service intervals (on BOV equiped cars) being my evidence.

Why do you think Nissan fitted BOV's? NVH? I don't think so, at the low standard boost levels there wouldn't be much to gain from that perspective. Emissions, if this was a atmospheric BOV versus recirculating, then emissions is certainly an issue. But we are talking recirculating BOV versus no BOV, I am stuggling to find any emissions advantage. If I refer to the Nissan workshop manual I can find no reference to a faulty BOV as being the potential for excessive emissions. That's evidence

I appologise for introducing reliability into a "performance" discussion, but a failed turbo does lead to pretty low "performance".

To finish first, first you must finish.