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Old 12-15-1999, 10:25 PM   #1
Ben
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Have a Nice Day? Blow off valve?

Does anyone fits a blow-off valve to the Legacy turbo ??
If you do , which one you install?
I know there are so many different blow-off valve in the market, could you guys tell me which one is the best for our "first and the only factory turbo in NA"?
Enjoy Your Legacy!!
(^_^)
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Old 12-16-1999, 03:55 AM   #2
Shik
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Ben, is your factory BOV leaking? I know at least up to 10psi mine works fine. It makes a nice "whoosh" sound as well when you put a cone filter on and locate it a bit closer to the intake( had to with the intercooler).
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Old 12-16-1999, 08:23 AM   #3
Miller3339
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I can't even hear mine over the exhaust and the Intake.
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Old 12-16-1999, 08:19 PM   #4
Submerk
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I have Apexi one want to sell but it's not good idle. I replace with 944 turbo by pass valve, it run really smoth and it cost only $30 at Porsche dealer. It is the same one as Turbonetics sell but they sell around $45.
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Old 12-16-1999, 08:21 PM   #5
Ben
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Me too, I don't think I could hear my blow-off valve sounds when change gear or relase the gas-padle!!
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Old 12-16-1999, 08:29 PM   #6
Ben
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Hi, Submerk: thanks for your info .I never know the 944 parts could fits to our turbo!!
But what happen to the Apex blow-off valve?
Does the idel drops after you install it?? Does the apex blow-off valve adjuctable??
Any other idea like HKS, Trust, or others?
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Old 12-16-1999, 11:21 PM   #7
Submerk
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The Porsche by pass valve is Bosch one, so they use in many car. It is easier to find in Porsche than other. Apexi is adjustable but it blow off atmospere, so you need to adjust idle and fuel to run smothly. For the stock blow off valve, try to turn up the boost, you will hear it.
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Old 12-17-1999, 07:07 AM   #8
Ben
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Will the Porsche blow-off valve sounds lound?
I'm looking for the blow-off valve that could have great sound!!!
I can't forget the first time I hear the lound sound from the WRX when it change gear!!(I heard it when I back to HK).
Thats why I needs to research which blow-off valve do have good sound and fits onto our car!!!
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Old 12-17-1999, 09:31 AM   #9
Submerk
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The sound is not gonna be like Greddy HKS or other aftermaket one but you can hear it. Try http://www.tap1.com, they have a nice blow off valve, and it costs about $175. This one is not blow off to atmosphere but it is adjustable. I think this unit like the one that BMP selling. If you want sound, buy Blitz or Apexi. Not only you will hear it, people on the street will hear it too. The problem with these is the idle.
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Old 12-17-1999, 09:09 PM   #10
Ben
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Whats the different between the atmosphere blow-off valve and bypass blow-off valve??
Which should I use for my car?
Submerk, are your blow-off use with intercooler or not??
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Old 12-17-1999, 11:00 PM   #11
Submerk
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Yes I use with intercooler. Buy the bypass valve and you will happy. You can buy the blow off valve, you will like the sound but you are not gonna like the idle.
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Old 12-18-1999, 08:08 AM   #12
PeteH
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The bypass valve will recirculate the air back into the intake tract while the BOV vents directly into the atmosphere, correct?

PeteH
'92 Turbo Legacy
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Old 12-18-1999, 01:25 PM   #13
Shik
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To be honest, I never thought there was a difference between the two, just different names for the same thing. For instance, the Group A Imprezas used the same BOV as ours but it had a filter on the end and vented to the atmosphere( The WRC Subarus always used a MAP set-up to meter air). Alot of the Mitsubishi guys use the HKS VPC( changes the MAS to MAP) but they keep the original BOV but then vent it to the atmosphere instead of recirculating it, but it is still the same valve.

Just as a side note, I don't think I would be able to put up with an external venting BOV. Mine is quite loud when I shift right now. It's funny because if someone not familiar with the car is inside and they hear it, they just look at me and ask " What the hell was that?" Although the ones that make the chirping sound are pretty neat.
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Old 12-20-1999, 06:28 AM   #14
Miller3339
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hey, could something be wrong with my car if I can hear it?? since I have the a more flowing exhaust, could that take away boost thus not needing the Blow by Valve??
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Old 12-20-1999, 03:55 PM   #15
Shik
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Miller, because of my intercooler, the distance the pressure has to travel from the intercooler pipe to the BOV back to the intake has been shortened quite a bit. Also my hoses for the BOV are very short and almost completely straight. I would think the way the factory had it would help break the sound up alot. My boost is also turned up about 1.5 psi from what it was from the factory so that may make it a bit louder as well.
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Old 12-22-1999, 01:17 PM   #16
Rob Deis
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The purpose of the blow-off valve is to vent the excess pressure in the intake stream that is created when the throttle plate closes suddenly.



When the throttle plate slams shut in any car, say because you're shifting gears, all the air that is flowing through the intake stream collides with it and suddenly stops. This created a large compression wave that travels back from the throttle plate all the way through the turbo and out the air filter. The more boost you're running, the bigger the compression wave will be.


This is hard on the turbo.



This also means that it will take longer for the turbo to spool when you get on the gas again.



The BOV vents the extra pressure caused by the compression wave, so the wave stops. This makes life easier for the turbo and allows it to spool faster.



There's great debate about whether you should vent to atmosphere or back into the intake upstream of the turbo, so I don't know for sure which spools better. Atmosphere will make better sound, for sure.



BOVs that create idle problems do so because they are leaking air at idle. The extra air isn't being measured by the MAF sensor (or whatever intake air sensor is used) so the ECU doesn't know about it and is putting in the wrong amount of fuel.
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Old 12-23-1999, 06:46 AM   #17
ScoobyMania UK
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Arrow

Which is exactly the problem caused by fitting a vent to air BOV where a recirculating BOV should be used.

Cause is that with vent to atmosphere, the engine isn't expecting the already measured air to disappear, (it is expecting it to recirculate) so fuels as if the air was still there.

The Car then runs rich, causing sooting of exhaust, possible Cat damage, popping & coughing on sudden deceleration and at each gear change, particularly when changing up.

Having said all that Vent to Atmosphere's do sound cool!

Mike.
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Old 12-23-1999, 08:44 AM   #18
Submerk
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Those your answer Ben. I had that problem before, so that's why I changed to bypass valve.
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Old 12-23-1999, 11:26 PM   #19
Ben
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It seems there only one choic to our suby!!
The bypass BOV is the things I could use to replace the OEM BOV???
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