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BOV Positioning 

 

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 Post subject: BOV Positioning
Posted: Fri Aug 14, 2009 3:56 pm 
Tyre Shredder
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Hi Fellas,

I'm in the process of fitting up a water/air intercooler to my AU. The core is now mounted where the battery used to be. I'm running the pipework back around from the supercharger outlet, across the front of the engine bay (above radiator), in/out of the core and straight up to the TB.

My question is, where is best for the BOV to go? Mine is the bosch plumb back type.

Thanks for the tips,
Joe

 

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 Post subject: Re: BOV Positioning
Posted: Sat Aug 15, 2009 6:05 pm 
Getting Side Ways
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Close to the thottle body, but some say it doesnt matter a real lot. A position that is easy to plumb back.
Here is where i re-did mine
Image
Tube runs over to the turbo inlet. I think there is another pic in the "show us your intake" thread

Cheers

Daz

 

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 Post subject: Re: BOV Positioning
Posted: Sun Aug 16, 2009 12:08 am 
Getting Side Ways
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Yep some will argue ?? That's it's better to dump hot air..
Imo it doesn't really matter .. It's there to prevent turbo surge..
Close to air cleaner helps with plumback...

 

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 Post subject: Re: BOV Positioning
Posted: Sun Aug 16, 2009 2:23 pm 
Getting Side Ways
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Depends on how much power you are chasing. I've never seen a falcon turbo 6 bend the throttle butterfly back (thus jamming it open) but it has happened on a few high powered cars in the US. In that case the BOV should be mounted close to the throttle body. Otherwise plumb it close to the turbo. You have to remember that when a BOV opens it relieves all of the pressure between the turbo and BOV. You still get some residual pressure between the BOV and the throttle body and you can use that to your advantage. For example on a manual car when performing a quick gear change it helps to have some positive pressure in the intake piping for when you crack the throttle open again. It might only be a bees d**k in it but until it has been quantified I'll stick by my argument.
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 Post subject: Re: BOV Positioning
Posted: Mon Aug 17, 2009 1:07 am 
Getting Side Ways
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The idea of a blow off valve is to keep the turbo from getting the bouncing air off the throttle blades.. The blades vertually shut BEFORE the BOV opens.. Its the vacuum when throttle is closed that opens BOV..
Turbo shafts break when sping over 100,000 rpm then have to spin in opposit direction..
With an auto trans there's no pint in having a super large BOV. Unless your after the wank factor!!
If you can remember about 6+ years ago Fordforums run a dyno day at Croyden Motorsport..
A guy Michael's car blew turbo and smoke came from every where...
The T04E turbo shaft snapped at the turbine wheel and oil just ran into HOT exhaust..
It never run a BOV and broke when coming off throttle.. Where this high air pressure bounces off the throttle body..

 

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As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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 Post subject: Re: BOV Positioning
Posted: Mon Aug 17, 2009 1:10 am 
Getting Side Ways
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The idea of a blow off valve is to keep the turbo from getting the bouncing air off the throttle blades.. The blades virtually shut BEFORE the BOV opens.. Its the vacuum when throttle is closed that opens BOV..
Turbo shafts break when spining over 100,000 rpm then have to spin in opposite direction..
With an auto trans there's no pint in having a super large BOV. Unless your after the wank factor!!
If you can remember about 6+ years ago Ford Forums run a dyno day at Croydon Motorsport..
A guy Michael's car blew turbo and smoke came from every where...
The T04E turbo shaft snapped at the turbine wheel and oil just ran into HOT exhaust..
It never run a BOV and broke when coming off throttle.. Where this high air pressure bounces off the throttle body..

 

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As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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 Post subject: Re: BOV Positioning
Posted: Mon Aug 17, 2009 7:54 pm 
Getting Side Ways
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For a turbo to spin backwards it first has to stop. Show me a data log of a turbo speed sensor fitted to a car with no BOV and then I'll believe you. I just can not believe that a turbo can spin up to 100,000rpm, stop, spin backwards, stop again, then get back up to 100,000rpm all under 1 second.

The zututututu sound is the pressure waves going back out of the turbo inlet (after they have bounced off the throttle butterfly), Not the turbo spinning backwards as most people would like to believe.
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 Post subject: Re: BOV Positioning
Posted: Mon Aug 17, 2009 11:31 pm 
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xcabbi wrote:
For a turbo to spin backwards it first has to stop. Show me a data log of a turbo speed sensor fitted to a car with no BOV and then I'll believe you. I just can not believe that a turbo can spin up to 100,000rpm, stop, spin backwards, stop again, then get back up to 100,000rpm all under 1 second.

The zututututu sound is the pressure waves going back out of the turbo inlet (after they have bounced off the throttle butterfly), Not the turbo spinning backwards as most people would like to believe.

YES thats what causes the damage to turbo..
The effect as you say on butterfly is wrong as it turns on centre so any pressure will be on BOTH sides.. Plus most throttle body blades are NOT 90* ..
Smaller turbo spin way past 100.000 rpm..

 

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As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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 Post subject: Re: BOV Positioning
Posted: Mon Aug 17, 2009 11:44 pm 
Tyre Shredder
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Hi all,

Thanks for the responses. I'm assuming this discussion on how BOV's affect turbos would be the same with my supercharger?

Currently my setup (with no intercooler) has the bosch plumb back positioned halfway between SC and TB. This is the standard capa setup. I've realised also that its not actually plumbed back at all....the exit tube runs down into the front spoiler and is sealed off with a sponge type sock.

For your reference its blowing around 10psi and I guess making 190ish rwkw.

In the pic below you can see where I've mounted the core, where the SC is, and a little dummied up pipework. This is where I'm up to now. In this setup, where do you think would be the best place to put the Bosch BOV? If I can put it between the SC and intercooler it would be easy as I could re-use the existing pipe holding the BOV....

cheers!
Joe

 

 

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File comment: Core
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 Post subject: Re: BOV Positioning
Posted: Tue Aug 18, 2009 12:04 am 
Getting Side Ways
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Would be nicer to have it vented to air cleaner..
But with map control ECU it won't matter too much..
With superchargers it depends where the throttle body is ??
Positive usually are outside blower .. While centrifugal are on manifold where blower
forces air through it..
In this case it also helps idle control..

 

_________________

As in ZOOM 126 edition
331 Dart block,3.25/ 4340 steel crank, Oliver rods,TFS ported track heat heads, TFS track heat inlet Twin SC61 turbo's
Project 1UZ-EF has started.. S475 Turbo 4.0 V8 Mustang Celica.....

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 Post subject: Re: BOV Positioning
Posted: Tue Aug 18, 2009 12:14 pm 
Tyre Shredder
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EBXR8380, or anyone else who knows (!), can you clarify this....I don't get what you mean? Mine is centrifugal, and TB is in the standard position as per engine bay pic.

I'm just keen to know on which stage of the pre throttle body pipework the BOV should be fitted to, if it matters at all. Basically I'm wondering should it be fitted between intercooler and throttle body (closest position to TB), or between supercharger and intercooler (closest to air cleaner)?

Also, what's the benefit of venting to the air cleaner? And how does BOV positioning help idle control?

Thanks again for the help!

Joe

 

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 Post subject: Re: BOV Positioning
Posted: Tue Aug 18, 2009 2:00 pm 
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I'd mount it pre-cooler, mainly because you've said it's easier and I think it's 6 of one, half dozen of the other...
You could argue that venting it before it goes through the cooler is going to be more efficient, but how much?

I think the thread got turned from BOV positioning to whether or not to run a BOV at all :lol:

 

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 Post subject: Re: BOV Positioning
Posted: Tue Aug 18, 2009 2:08 pm 
Tyre Shredder
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Heheh...hence my confusion. Cheers!

 

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