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Location:
Rocklea qld
Registered:
February 2003
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BOV. is it needed??
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Sun, 10 April 2005 11:08
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just wondering if a BOV is needed or if you can run without them?? currently its gonna be on a 18rg turbo but to get the car running im not gonna be using a intercooler. just straight from the turbo into the throttle body. can i get away with no BOV until i fit my intercooler gear.
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Location:
Sydney
Registered:
February 2003
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Location:
Adelaide
Registered:
July 2002
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Re: BOV. is it needed??
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Sun, 10 April 2005 11:56
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ohhh wont there be like mega shock when u close the throttle after a nice WOT squirt??
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Location:
Brisbane
Registered:
May 2002
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Re: BOV. is it needed??
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Sun, 10 April 2005 12:02
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At low boost with no IC it will be fine. Most non-intercooled turbo cars were never fitted with a BOV from the factory, it's really not necessary.
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: BOV. is it needed??
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Sun, 10 April 2005 16:18
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BOV does help performance a bit though as itll help keep the turbo spinning on gear changes.
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Location:
Brisbane
Registered:
May 2002
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Re: BOV. is it needed??
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Sun, 10 April 2005 23:00
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No, it does no such thing. In some circumstances a BOV will actually decrease performance because it's releasing boost pressure every time you change gears.
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Location:
Sydney
Registered:
October 2003
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Re: BOV. is it needed??
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Sun, 10 April 2005 23:15
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I'd like to hear your explanation of the purpose Norbie (or a link to your source material) as everything I have ever read leads me to believe they're there to prevent intake pressure spikes and hence compressor surges.
It is true though that you don't need one and I doubt there'd be a noticible difference in performance either way. But I would imagine stopping the turbo from slowing dramatically can only be a good thing for turbo life.
The ST185 was a car that was intercooled from factory with no BOV
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Location:
Parramatta
Registered:
July 2002
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Re: BOV. is it needed??
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Sun, 10 April 2005 23:44
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davedave,
I am in agreeance with you here sorry norbie but every thing that i have read and been told is for the reasons that davedave stated.
i have not heard [QUOTE]n some circumstances a BOV will actually decrease performance[/QUOTE
Can you direct me to where you heard / read that because if this is the case i really would like to know. (not having a shot just wanna know where because thats intresting)
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Location:
Brisbane
Registered:
May 2002
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Re: BOV. is it needed??
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Mon, 11 April 2005 00:17
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Note I'm talking about low-boost non-intercooled factory setups here. If you have a big intercooler and you're running lots of boost (like me), a BOV is a good thing. That's why I have one.
I stand by my assertion that a BOV is not a performance modification though. Its purpose is to increase reliability and decrease noises in factory cars which new buyers might find disconcerting.
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: BOV. is it needed??
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Mon, 11 April 2005 02:24
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an ST185 DOES have a BOV AFAIK... it's what toyota call an "ABV".
I am agreeing with Norbie.
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Location:
Brisbane, Queensland
Registered:
January 2004
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Re: BOV. is it needed??
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Mon, 11 April 2005 02:35
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| THE WITZL wrote on Mon, 11 April 2005 12:24 |
an ST185 DOES have a BOV AFAIK... it's what toyota call an "ABV".
I am agreeing with Norbie.
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news to me. they didn't run any kind of by pass valve.
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On Probation
Location:
Charnwood
Registered:
March 2005
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Re: BOV. is it needed??
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Mon, 11 April 2005 02:36
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u wanna get da blo off valve rated to da most horse powa so it duzn hold back tha grunt of ya car. i use a blo off valv rated to 700 hp. anythin less and u will suffa
da chicks dig da sounds to man
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Location:
Sydney
Registered:
October 2003
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Location:
Rocky Mountains, Canada
Registered:
May 2002
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Re: BOV. is it needed??
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Mon, 11 April 2005 02:42
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| davedave wrote on Mon, 11 April 2005 12:08 |
I agreed that there's no real performance gain, but I disagreed that the BOV doesn't help to let the turbo continue to spin.
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Ok.
So you agree that the BOV does help keep the turbo spooled, but also think that it actually doesnt make that much of a difference?
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Location:
Brisbane, Queensland
Registered:
January 2004
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Re: BOV. is it needed??
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Mon, 11 April 2005 02:45
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davedave: only the st205 had a bypass valve stock from factory.
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Location:
Sydney
Registered:
October 2003
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Re: BOV. is it needed??
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Mon, 11 April 2005 02:50
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| M.W.P. wrote on Mon, 11 April 2005 12:42 |
Ok.
So you agree that the BOV does help keep the turbo spooled, but also think that it actually doesnt make that much of a difference?
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I don't think it would be noticable either way on a stock application (I could be wrong though). But dependant on the turbo/boost/intake-piping I think each application would be different.
Cheers,
Dave "fence sitter"
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Location:
Brisbane
Registered:
May 2002
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Re: BOV. is it needed??
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Mon, 11 April 2005 04:15
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A BOV is going to make SFA difference to how fast the turbo spins on gearchanges. You need to be aware it takes quite a lot of power to keep a turbo spinning at any meaningful rpm, and as soon as you lift off the throttle there is no longer any significant exhaust flow, hence no longer any power available to the turbine - so BOV or no, that sucker is going to slow down pretty much immediately.
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Location:
Adelaide
Registered:
September 2003
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Re: BOV. is it needed??
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Mon, 11 April 2005 04:47
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| studman wrote on Mon, 11 April 2005 12:06 |
u wanna get da blo off valve rated to da most horse powa so it duzn hold back tha grunt of ya car. i use a blo off valv rated to 700 hp. anythin less and u will suffa
da chicks dig da sounds to man
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I hope that this is a joke. If so, Haha  
If not, type properly and get a life.
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Location:
Sydney
Registered:
October 2003
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Re: BOV. is it needed??
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Mon, 11 April 2005 04:55
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But surely a turbine that is still trying to build pressure is going to slow down much faster than one that has had its pressure relieved. And hence would stop rapid changes in the speed of the turbo.
I have a little AVI of myself plugging a vacuum in to the back of a turbo and it takes a few seconds to spin up to terminal velocity, then once removed a few seconds to spin down. I'm sure that if there were a wall of pressure behind it that it was continuing to compress, it would stop very sudden.
Again, I agree that it would have little effect on performance, but disagree with the fact that you think BOV and BOVless systems would spin at the same speed between changes.
I'm not trying to be arguementative, just trying to get a better understanding of it myself.
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Location:
Adelaide
Registered:
July 2002
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Re: BOV. is it needed??
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Mon, 11 April 2005 05:35
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if they are useless and not worth having then why do *most* factory turbo cars have them? since when do manufacturers put in useless components for the hell of it.
they are there to protect the turbo so that it will last longer and be more reliable. It will not give u extra killerwats thats not wat its about, i would not call a BOV a performance accesory, its kinda like an oil cooler, its not going to make ur car go faster but it will make it last longer.
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Location:
Central Coast, NSW
Registered:
February 2005
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Re: BOV. is it needed??
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Mon, 11 April 2005 05:36
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| Hunty wrote on Mon, 11 April 2005 15:35 |
i would not call a BOV a performance accesory, its kinda like an oil cooler, its not going to make ur car go faster but it will make it last longer.
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So what about the cars that don't come with one fitted?
Should we go out and buy one?
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Location:
Adelaide
Registered:
July 2002
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Location:
Brisbane, Queensland
Registered:
January 2004
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Re: BOV. is it needed??
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Mon, 11 April 2005 05:55
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well have a think about, whats the other reason to put on a BOV? to reduce noise. (by reduce noise i mean plumback, like all manufacturer cars)
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Location:
Melb, Victoria
Registered:
April 2004
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Re: BOV. is it needed??
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Mon, 11 April 2005 10:21
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just to clear things up:
1st gen 3sgte (st165), 2nd gen 3sgte/jdm/aussie delivered including carlos saintz (st185) all had no type of bpv/bov fitted.
2nd gen 3sgte (mr2) and 3rd gen gt4's had them though.
| Hunty wrote on Mon, 11 April 2005 15:35 |
if they are useless and not worth having then why do *most* factory turbo cars have them? since when do manufacturers put in useless components for the hell of it.
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I agree.Car makers are always trying to make there product cheaper and cheaper, so why would they spend extra money on designing/fabricating and fitting useless parts?? they wouldn't.
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Location:
Perth
Registered:
July 2004
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Re: BOV. is it needed??
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Mon, 11 April 2005 15:50
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I turbo is not a sealed pump..
air can flow backwards while it is still spinning...
not that I know anything in either case..
but I would really like to read some tech docs on BOV vs non BOV applications.
why is it better to run a BOV with a cooler and more boost?
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Location:
Brisbane
Registered:
May 2002
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Re: BOV. is it needed??
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Mon, 11 April 2005 23:15
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With a FMIC you have a much larger volume of pressurised air between the turbo and the throttle body, so combine this with increased boost and you end up with pretty large pressure spikes when the throttle snaps shut at full noise, much larger than any factory engine would experience.
I have a very large FMIC and when I cranked the boost up to 18psi I started popping intercooler hoses off occasionally, even with the factory BOV. I have since installed a much larger BOV and the problem has gone away; the only down side is my car sounds like a city bus now. 
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Location:
brisbane
Registered:
October 2004
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Re: BOV. is it needed??
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Tue, 12 April 2005 00:21
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how about doing a search, this topic has been around a few
times and got pretty heated lol
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I Supported Toymods
Location:
Sydney
Registered:
December 2002
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Re: BOV. is it needed??
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Tue, 12 April 2005 01:44
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Note:
The ST185 Standard and Group A do not have a factory BOV.
The ST205 has a BOV which goes from the IC to the airbox which they call an air bypass valve.
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Location:
Canberra
Registered:
June 2003
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Re: BOV. is it needed??
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Tue, 12 April 2005 02:00
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OMG how much ill informed info is out there on BOV's 
1st up, no ST185 ever came with a factory BOV.
Manufacturers who use BOV's do so for only one reason...to reduce noise. All factory BOV are recirculating, they are there to prevent reversion of the intake charge back thru the turbo which makes that lovely fluttering noise. Some may like it but manufacturers do not. Actually i tell a little lie there, for homologated models like the 205 the BOV was also there to feed the antilag system...sneaky buggers.
In very high boost applications this intake reversion (or more accurately the pressure wave reflected off the closing butterfly)can supposedly 'shock' the compressor wheel and cause a shaft failure. I have never seen this happen (and i have run some pretty decent boost levels) but have heard 3rd hand of it happening on a big boost circuit car. Sounds possible but it is obviously very rare. The other reason is as Norbie states that the pressure spike can pop hoses...of course Norbie could just shell out for decent clamps and it wouldn't be an issue
Now, i have done with and without BOV testing and can confidently state that the preformance gain or loss is so small as to be of no consequence. I actually had a very small drop in performance as the intake piping had to refill after every BOV vent. The turbo does this very fast so you couldn't feel any difference but by the clock i dropped a 0.1-0.2 secs off 0-100 kph (Haltec data log).
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.
Hope that clears up some of the misinformation.
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I supported Toymods
Location:
Epping, Sydney
Registered:
May 2002
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Re: BOV. is it needed??
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Tue, 12 April 2005 02:21
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could you inform JUN and HKS? I'm sure they'd like to know the bov on their drag & circuit cars are useless.
alright, maybe that was a bit sarcastic.
I like the theory behind your statement, but find it hard to believe that top tuning houses are fitting useless items to their $100+k engines.
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Location:
Brisbane
Registered:
February 2003
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Re: BOV. is it needed??
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Tue, 12 April 2005 02:47
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Justen are you saying that by not running a BOV on a turbo car, you a not creating anymore wear on the turbo than if a BOV was fitted?
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Location:
Brisbane
Registered:
May 2002
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Re: BOV. is it needed??
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Tue, 12 April 2005 02:57
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| draven wrote on Tue, 12 April 2005 12:21 |
I like the theory behind your statement, but find it hard to believe that top tuning houses are fitting useless items to their $100+k engines.
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I don't find it hard to believe at all. If customers expect their $100k turbo engine to have a BOV (and let's face it, 99% of buyers will expect just that), you can be sure they will fit one. Whether the engine will lose performance without a BOV is another matter entirely.
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I supported Toymods
Location:
Adelaide
Registered:
July 2004
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Re: BOV. is it needed??
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Tue, 12 April 2005 04:13
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GZ20's are also a car that comes factory fitted with an intercooler and does not have a factory plumback
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Location:
Central Coast, NSW
Registered:
February 2005
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Re: BOV. is it needed??
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Tue, 12 April 2005 04:18
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| MR 1GGTE wrote on Tue, 12 April 2005 14:13 |
GZ20's are also a car that comes factory fitted with an intercooler and does not have a factory plumback
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I was gonna say something but didn't want to be shouted down if I was wrong 
bitchin maen, i'm g0nna put me a p0d filtah on mah car and get da hektik flutter when i let off the accelerator yo[/idiot mode]
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I supported Toymods
Location:
Adelaide
Registered:
July 2004
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Re: BOV. is it needed??
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Tue, 12 April 2005 04:20
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| Merudo wrote on Tue, 12 April 2005 13:48 |
| MR 1GGTE wrote on Tue, 12 April 2005 14:13 |
GZ20's are also a car that comes factory fitted with an intercooler and does not have a factory plumback
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I was gonna say something but didn't want to be shouted down if I was wrong
bitchin maen, i'm g0nna put me a p0d filtah on mah car and get da hektik flutter when i let off the accelerator yo[/idiot mode]
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I had a pod on mine, the flutter is rather miniscule...
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Location:
Central Coast, NSW
Registered:
February 2005
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Re: BOV. is it needed??
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Tue, 12 April 2005 05:15
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| MR 1GGTE wrote on Tue, 12 April 2005 14:20 |
| Merudo wrote on Tue, 12 April 2005 13:48 |
| MR 1GGTE wrote on Tue, 12 April 2005 14:13 |
GZ20's are also a car that comes factory fitted with an intercooler and does not have a factory plumback
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I was gonna say something but didn't want to be shouted down if I was wrong
bitchin maen, i'm g0nna put me a p0d filtah on mah car and get da hektik flutter when i let off the accelerator yo[/idiot mode]
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I had a pod on mine, the flutter is rather miniscule...
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ahh i was just mock pretending to be a tool... i dont really care about such things
Though it does sound cool
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Location:
Canberra
Registered:
June 2003
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Re: BOV. is it needed??
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Tue, 12 April 2005 05:42
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DRAVEN - never said they were useless but failures are very few and far between even on big boost cars when not fitted. The other thing you might consider is why "tuning houses" are racing. Their cars are driving billboards to sell their products...pretty stupid not to run your own BOV eh  They also run earth straps...must be mega horsepower in those
MONKEY DUDE - i would say any extra wear from not running a BOV would be negligible...there may be some but hard to quantify.
For what it's worth i run a massive BOV...mainly to try and quieten down the extremely loud reversion i get thru my twin turbo setup. If there's extra wear benefits or less likihood of failure as well....great, not worth stressing about either way though.
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Registered:
December 2003
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Re: BOV. is it needed??
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Tue, 12 April 2005 05:50
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Never ben able to measure any PERFORMANCE difference between having a bov or not, but that phsst sound do make my penis much bigger. 
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Location:
Rocklea qld
Registered:
February 2003
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Re: BOV. is it needed??
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Tue, 12 April 2005 08:19
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geez. I opened up a hot topic hear didnt I. for some more info im only planing on running the engine with no intercooler or BOV for a few weeks. then its on with the FMIC, BOV and wind it up to 20 psi and go holden hunting.
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Location:
melbourne
Registered:
February 2005
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Re: BOV. is it needed??
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Tue, 12 April 2005 12:22
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the mitsubishi starion didnt run a bov or i/c either ran straight into the inlet manifold....
i think ppl put bov's to make them think that there safe or to say wow check out my shiny dick thing i got here.... or too help the cops find it in ur engine bay because it sits up like something that something and yeah...
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Location:
Wahroonga
Registered:
June 2003
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Re: BOV. is it needed??
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Tue, 12 April 2005 13:14
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get a NA engine and u don't need to have a BOV. Anyone that has a BOV ona NA engine should be shot.
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