Who is NOT running a BOV? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 05-19-2010, 02:09 PM   #1
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Default Who is NOT running a BOV?

I just upgraded my cold side piping from 2" to 2.5" (For mad horsepowerzz)
And since I didnt feel like doing any welding at the moment, I now am running with no BOV.
I know the general consensus is that at low boost you dont need one, but at high boost you do. But, I have no reason to believe this is actually true, in addition to the fact that there are lots of examples of high boost cars running without them for seemingly long periods of time.
So because of this I dont think I am going to bother putting a BOV back on.

So, 2 questions:
1) Am I alone?
2) Am I crazy?
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Old 05-19-2010, 02:15 PM   #2
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These guys didn't run a BOV and it worked well enough for them
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Old 05-19-2010, 02:16 PM   #3
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Quote:
Originally Posted by Full_Tilt_Boogie View Post
So, 2 questions:
1) Am I alone?
2) Am I crazy?
Yes and Yes.

OEMs run them for a reason. Namely because they have warranties to watch-out for. I am sure that some guys somewhere got away without one. But a lot of engineers much smarter than I think they are an absolute neccesity. My logic there is some of the absolute crap OEM turbo setups out there. Where the cheaped out as much as they could. Yet even then they still had a BOV.

IIRC you can get a short section of pipe from places like ATP thats already flanged for a BOV. Just cut out a section from your pipes, put a lip on there, get yo-sef some clamps and silicone and viola, BOV without welding.

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Originally Posted by kday View Post
These guys didn't run a BOV and it worked well enough for them
Time between engine/turbo rebuilds?
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Old 05-19-2010, 02:29 PM   #4
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I've heard people argue that they're not needed every now and then, but when 99.9% of all turbocharged cars in the whole world use them I'm going to go with "yes, they are required"
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Old 05-19-2010, 02:37 PM   #5
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How else would you avoid compressor surge?
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Old 05-19-2010, 02:39 PM   #6
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One could argue that OEM cars have them today because of the flutter/turkey gobble.
I havent gotten into boost at all yet, but just letting off the throttle with my boost gauge reading atmospheric and I get a couple seconds of fluttering sound, which would be totally unacceptable for a factory vehicle.
Also, what about the OEM turbo vehicles before BOVs were standard? Did they tear though turbos constantly? I doubt it.

Im not trying to be close minded, I ant this to be an open forum, but I have never seen any evidence of damage from compressor surge, and neither has Corky.
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Old 05-19-2010, 02:43 PM   #7
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Heres some RX7 folks, many of whom are running without them. They seem to have drawn the same conclusion as myself.
http://www.fdowners.com/showthread.php?t=217
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Old 05-19-2010, 02:47 PM   #8
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Quote:
Originally Posted by Sparetire View Post
Time between engine/turbo rebuilds?
Presumably after every rally. But one rally worth of turbo abuse is probably more than a street car will see in its lifetime...

The OEM argument isn't too convincing since NVH is a major issue for OEMs, and the "turkey gobble" is definitely a NVH problem.
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Old 05-19-2010, 02:49 PM   #9
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Very interesting. I do find compressor surge annoying though, so I'll keep mine.
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Old 05-19-2010, 03:14 PM   #10
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NVH is pretty much handled with the retarded intake tracts you tend to see on factory vehicles. They have to have these to avoid spooling sounds anyway, and recircing just before the turbo also creates noise there. I could hear my bone stock DSMs BOV quite well as soon as I removed a lot of crap from the intake tract and left it recirced to the stock location just before the turbo. So I dont think the noise component is the reason. Though I can see the point that a car is much more driveable with one, which may actually be the primary reason the OEMs run them. On the other hand, I have 0 trouble beleiving that many pre-BOV OEM turbo cars were nightmares in terms of relaibility, or at least would be by modern standards. People used to think 100K was super high mileage and that any car lasting that long was great.
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Old 05-19-2010, 03:21 PM   #11
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Quote:
Originally Posted by Full_Tilt_Boogie View Post
1) Am I alone?
No, anyone who has a standard BEGi-S kit doesn't have a BOV either, but then again, they're running 5-6psi.

In BEGi's description it says:

Quote:
Bypass Valve: The Bypass valve is used to eliminate compressor surge. On the smaller turbo, GT2554, it is not a necessity. However, it is a good idea for the larger turbos.
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Old 05-19-2010, 03:24 PM   #12
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Of course the Rotary guys don't care about the longevity of their turbos, the apex seals will be gone long before they have to worry about the turbo.

I'd like to see spool data with and with out.
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Old 05-19-2010, 03:25 PM   #13
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I'd like the "surging doesn't cause damage" argument be proven. By that I mean: we all know knock causes engine failure. Enough of it and you blow your **** up. and YET lots of cars run with a bit of knock here and there for their whole lifetime. So can it be the same thing here?

low pressure and you probably can get away with it, yet raise it and you MAY damage stuff?
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Old 05-19-2010, 03:43 PM   #14
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Quote:
Originally Posted by Sparetire View Post
Time between engine/turbo rebuilds?
Exactly. The rally guys do without BOVs because they want to eliminate lag as much as possible for better throttle modulation, and retaining pressure in the intake plumbing helps with that. Another anti-lag trick they use is to retard off-throttle ignition timing to the extent that much of the fuel charge burns in the turbine housing, which helps fight the compressor surge to keep the turbo spun up. IDK how much the timing retard versus the lack of BOV contributes to their reduced turbo service intervals. Those teams also have budgets massive enough that they can practically ignore service life, whereas my budget had me thinking long and hard about dropping a couple hundo on a TiAL Q and adapter pipe.

I am open-minded though. I think you'd be a bit of a guinea pig on this forum running without one but I'd be curious to hear some long-term results.
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Old 05-19-2010, 03:50 PM   #15
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Quote:
Originally Posted by 18psi View Post
I'd like the "surging doesn't cause damage" argument be proven. By that I mean: we all know knock causes engine failure. Enough of it and you blow your **** up. and YET lots of cars run with a bit of knock here and there for their whole lifetime. So can it be the same thing here?

low pressure and you probably can get away with it, yet raise it and you MAY damage stuff?
I would like the "surging does cause damage" argument proven.

With axial turbines compressor stall can cause premature wear if it occurs for long periods of time because it causes more vibration.
Whether or not this is true for radial turbines, I dont know.

We can safely assume that if a turbo is in constant surge non-stop, that the vibrational issues would cause damage over some amount of time.
But that not what is happening, for our application its only surging for a second or two.
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Old 05-19-2010, 03:51 PM   #16
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1. No

I am running without BOV, but i'm only running @ 6 psi. It is plumbed for a BOV, but not for recirculating (stock Greddy intake elbow). I plan on running it this way until I increase the boost.
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Old 05-19-2010, 04:21 PM   #17
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My Grand Nationals didn't have a BOV.
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Old 05-19-2010, 04:51 PM   #18
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http://www.turbobygarrett.com/turbob...r/faqs.html#t9

Quote:
What is compressor surge?
The surge region, located on the left-hand side of the compressor map (known as the surge line), is an area of flow instability typically caused by compressor inducer stall. The turbo should be sized so that the engine does not operate in the surge range. When turbochargers operate in surge for long periods of time, bearing failures may occur. When referencing a compressor map, the surge line is the line bordering the islands on their far left side.
Compressor surge is when the air pressure after the compressor is actually higher than what the compressor itself can physically maintain. This condition causes the airflow in the compressor wheel to back up, build pressure, and sometimes stall. In cases of extreme surge, the thrust bearings of the turbo can be destroyed, and will sometimes even lead to mechanical failure of the compressor wheel itself.
Common conditions that result in compressor surge on turbocharger gasoline engines are:

* A compressor bypass valve is not integrated into the intake plumbing between the compressor outlet and throttle body
* The outlet plumbing for the bypass valve is too small or restrictive
* The turbo is too big for the application
The shop I work for has seen many turbos killed by compressor surge. It will wear out your thrust bearing over time, and at the very least create a nice oil leak/smoke screen in the process. We stress to our customers that a BOV needs to open at anything above 2-3psi or surge may be created, and while ithat may seem to be a minor amount of pressure, over time it's still going to hammer away at the thrust bearing surface.
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Old 05-19-2010, 06:12 PM   #19
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Quote:
Originally Posted by TurboTim View Post
My Grand Nationals didn't have a BOV.
Agreed, but that was back when mullets and Camaros ruled the earth.
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Old 05-19-2010, 07:17 PM   #20
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Mullets still rule.

Many people I drive with dont run BOV either. They said the effect is minimal and worth it not having to worry about one more thing..

I have a big *** Tial BOV
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