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You may wanna search this was coverd in depth recently. Basically you only need one if you have blocked the factory PCV system in some way such as an IC or a none stock TB.
 

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Just as Shawn said. 90% that have them are just for show. Only need if you blocked the PCV passages. I need one cause I have the LS1 TB and teh adapter plate blocks the PCV passage to the TB.
 

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Mike Kopstain said:
Also keep in mind that if your stock PCV system is in tact and you add breathers you are creating a fairly significant vacuum leak which in the very least makes tuning interesting. :)
Now that I havent heard. I thought the breather was for the preasure to excape. I didnt think anything gets sucked in, there for you would not have a vaccum leak.
 

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Yeah why would there be any vacuum in your valve covers? I've put my hand over the oil fill hole in the cover after I changed my oil and didn't feel any suction.
 

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I agree with merc I do not think thats the case. If your valve covers are under a vacuum where comming from?
 

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On a good engine there is supposed to be NO vacuum in the block...the PCV is designed so that BLOW BY can escape without harming the engines gaskets, thus the name POSITIVE Crank Ventilation. You shouldn't feel ANYTHING. If you feel suction then check your intake gaskets because one or more may be bad. If you feel air BLOWING OUT then it's likely that your piston rings/cylinder walls are shot and there is TOO MUCH blow by. ;)
 

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Howdy all,


The benefit of these breathers is that they help evacuate
added crankcase pressure that is created by added blow-by
which is a side effect of added boost. They also become necessary with some intercoolers that block off p.c.v. passages.

BIG JEFF
 

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without a breather there WOULD be vacuum in the block. The supercharger housing, where the PCV valve is located, is under negative pressure, and will place te entire crankcse inder negative pressure if the intake of the PCV system is blocked, like with an LS1 TB. If you'd like to read a more detailed outline of the system, i explained it here, i dont feel like retyping it.
http://www.regalgs.org/forum/viewtopic.php?t=15855
 

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I think what mike said is partially true. The pcv valve has vacuum on it. and It uses this vacuum to pull pressure from the crank case. There is a fresh air inlet to your crankcase. It is a drilled passage in the throttle-body asm. If this passage were to become plugged off. IE a Intercooler,LS1 throttle body etc. You WILL build a vacuum in the crank case. Because you blocked off the fresh air inlet. The reason the fresh air inlet is a passage in the throttle body is so the air the that the crankcase then through the pcv valve can be metered by the Mass Air Flow sensor. What causes the Tuning problem is this. If you use a filter on a stock throttle body system you are now inducing an unmetered air supply to your engine. This causes a lean condition (negative Long term fuel trim numbers)
Witch can easily be cured by a miniAFC or pcm programming.
In closing I would Recommend against a breather in the crankcase if the stock fresh air supply to the crankcase has not been compromised
 

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i block the TB hole in my tb and then drilled the tb into that channle so the tb jsut vents as normal only into the motor bay. im running NA for the moment no troubles
 

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FastGS88 said:
without a breather there WOULD be vacuum in the block. The supercharger housing, where the PCV valve is located, is under negative pressure, and will place te entire crankcse inder negative pressure if the intake of the PCV system is blocked, like with an LS1 TB. If you'd like to read a more detailed outline of the system, i explained it here, i dont feel like retyping it.
http://www.regalgs.org/forum/viewtopic.php?t=15855
well I find that odd considering when we did dave's car he forgot the breather and it was blowing out around the oil fill cap hence thats positive pressure on the crank case. Also several club gp memebers have blocked thier pcv without breathers and blown oil out the dipstick tube.
 

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When I did my gen5 with lsi I blocked the pcv fresh air. Within seconds I had such a large vacuum on the engine that it effected running. I pulled off oil cap (barley) and released all the vacuum!
 

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yup, thats what happens Chris. Usually itll make a horrendous squealing noise too because the engine is trying to suck the VC gaskets into the engine.

Mat
 

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Okay...I don't know about forced induccion cars but N/A cars EACH AND EVERY ONE that I have ever worked on has had POSITIVE Pressure, I have seen Negative pressure on only ONE car and he had an intake gasket that was bad, I fixed it a whala..perfect....Hell, the name of the system is POSITIVE CRANK VENTILATION..It's for a reason don't you think. ;)

BTW- as I stated, I have never worked on a forced induccion car so I don't know if the rules change.
 

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GT-ER said:
Okay...I don't know about forced induccion cars but N/A cars EACH AND EVERY ONE that I have ever worked on has had POSITIVE Pressure, I have seen Negative pressure on only ONE car and he had an intake gasket that was bad, I fixed it a whala..perfect....Hell, the name of the system is POSITIVE CRANK VENTILATION..It's for a reason don't you think. ;)

BTW- as I stated, I have never worked on a forced induccion car so I don't know if the rules change.
well on a camaro is you just add FI the dip stick will pop out unless you block the PCV and get a breather
 

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any car with a PCV valve will build negative pressure in the crankcase, BUT on some cars it might not be enough to make the valve covers squeal, BUT once you go WOT it would shoot the dipstick since blowby would be too much to be evacuated by the PCV valve alone.

Mat
 
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