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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1551
Location: Somerset, UK

PostPosted: Wed Sep 20, 2017 6:19 am    Post subject: Reply with quote

Why do you think you need a recirc or atmosphere bov? Whatís wrong with a closed system?
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1004
Location: The Netherlands

PostPosted: Wed Sep 20, 2017 6:28 am    Post subject: Reply with quote

I also have a recirculation valve.

What I have heard is that:
You need one to get rid of the air when you go of the gass/ throttle body suddenly closes. Otherwise you can damage your turbo.

All the turbo cars I owned had one, 944 turbo, Audi TT, Vag tfsi etc.
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937 trackday car
Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1551
Location: Somerset, UK

PostPosted: Wed Sep 20, 2017 6:31 am    Post subject: Reply with quote

Internet myths
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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924-76  



Joined: 05 Jun 2006
Posts: 1355
Location: Ontario, Canada

PostPosted: Wed Sep 20, 2017 6:36 am    Post subject: Reply with quote

We have one on a stock 931. I was asking what to use if I go with a 951S turbo.
And yes, I believe we need one to avoid unnecessary stress on the turbo.
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1976 924 N/A ROW SOLD
1980 931S
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1551
Location: Somerset, UK

PostPosted: Wed Sep 20, 2017 7:00 am    Post subject: Reply with quote

What stresses?
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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924-76  



Joined: 05 Jun 2006
Posts: 1355
Location: Ontario, Canada

PostPosted: Wed Sep 20, 2017 7:17 am    Post subject: Reply with quote

Compressor Surge:https://www.youtube.com/watch?v=vuyJ5jD3r0o
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1976 924 N/A ROW SOLD
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Wed Sep 20, 2017 7:33 am    Post subject: Reply with quote

Yep, I know. But why do we need bov on our cars? Just because stock cars are fitted with them, Do we need them? Why do manufacturers fit them? Reduce or increase noise? Turbo longevity? Why do tuners fit them but racers donít?

Why dump boost on gear shifts only to try and refill the intake with more boost? Only increases lag.
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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924-76  



Joined: 05 Jun 2006
Posts: 1355
Location: Ontario, Canada

PostPosted: Sat Sep 23, 2017 11:17 pm    Post subject: Reply with quote

I have to admit that this discussion went beyond my technical knowledge. I cannot explain why Porsche engineer deemed necessary to have a recirculation valve on the 924 turbo. All I can do is trust their judgement.

The stock 924 turbocharger have the recirculation valve directly build onto it. The 944 turbocharger do not, that's why I was asking what/how to address this. Answer from member who went that way was simple, install one.
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Sat Sep 23, 2017 11:53 pm    Post subject: Reply with quote

I was fishing for a wider opinion from others. Not directed at yourself. Internet is awash with bov opinion and myth. Manufacturers put them on for noise suppression on road cars. Tuners put them on for increased blow off noise. Racers bin them off in most cases as why would you dump good useable boost only to refill the intake with more air increasing lag. Iíve run my car with and without the recirc valve. It increases boost noise but also increases throttle response. You takes your choice. Just wanted to debunk the idea you must run a bov.
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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924-76  



Joined: 05 Jun 2006
Posts: 1355
Location: Ontario, Canada

PostPosted: Sun Sep 24, 2017 12:08 am    Post subject: Reply with quote

I really appreciate your comments and now see how you were fishing the wider community for more option.

If I was to take a guess as why racer don't run BOV or recirculation valve, I would say that they care more about the 1 or 2 second they could shave off a lap then having to rebuild a turbo. A road going car would be more on the safe side and worry more about turbo long life then the fraction of second they could shave off the drive to the next red light.
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1976 924 N/A ROW SOLD
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Sun Sep 24, 2017 2:18 am    Post subject: Reply with quote

Find someone who can genuinely say their closed circuit turbo system broke their turbo. Ive spoken to several guys whom race / demonstrate their 80ís Porsche race cars and period Sierra Cosworth RS500ís. They said they havenít replaced turbos for years despite spanking their high boost cars on historics events.
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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WEASEL149  



Joined: 19 Aug 2005
Posts: 592
Location: UK, Sheffield

PostPosted: Mon Sep 25, 2017 4:04 am    Post subject: Reply with quote

Carrera RSR wrote:
Find someone who can genuinely say their closed circuit turbo system broke their turbo. Ive spoken to several guys whom race / demonstrate their 80ís Porsche race cars and period Sierra Cosworth RS500ís. They said they havenít replaced turbos for years despite spanking their high boost cars on historics events.


Yep, I believed the myths until I looked into it properly.

Myths perpetuated by the aftermarket wanting to push their products.

There's more chance of a leaking BOV causing turbo destruction than offload surge in a closed system.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1551
Location: Somerset, UK

PostPosted: Wed Sep 27, 2017 7:33 am    Post subject: Reply with quote

1.8T in a 924 drag car under build currently. Closed system https://youtu.be/t0jBmNR6vq4
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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924-76  



Joined: 05 Jun 2006
Posts: 1355
Location: Ontario, Canada

PostPosted: Thu Sep 28, 2017 9:48 pm    Post subject: Reply with quote

Interesting topic, I'm glade you drag me into this.
More I read about it, more conflicting information I found.
Thanks
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1976 924 N/A ROW SOLD
1980 931S
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1551
Location: Somerset, UK

PostPosted: Fri Sep 29, 2017 4:20 am    Post subject: Reply with quote

I ran for several weeks my car with a closed recirc valve. The car does drive differently which may not be to everyones taste or driving style. I switched back to open recirc valve because I encountered a problem which I thought was closed system related but was not. I haven't gotten around to closing it off again. The car holds more boost between gear changes, but you do get some 'push' in the car after you come off the gas. As they say, every action as a equal reaction. So you have to chose whether open or closed works for you.
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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