PCV and breathers question
Thread Starter
Melting Slicks
Joined: Oct 2000
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From: Na
PCV and breathers question
Would there be a problem with using a breather on the driver side valve cover only? I have a 400 sbc with a modded LT-1 intake to work on a non lt1 block (lt1intake.com). If you are fimiliar with LT-1 pcv system then you know the pcv valve mounts in the intake itself not on the driver side valve cover. The valve covers I want to buy (like most other covers) have holes on the driver side and pass side for PCV provision. I am ok with the pass side valve cover but I am left with a hole in the drivers side cover. Can I just place a breather in the hole or will that cause a vacuum leak detectable by the MAF???
Team Owner
Joined: May 2002
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
I'm not familiar with the lt1 setup... but a pcv vent line should never be open to atmosphere on a MAF car. The pcv system needs a metered air source to suck from. If that source is closed off, you'll suck oil into it, if that source is topped with a breather, you have a vacuum leak.
Drifting
Joined: Jan 2002
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From: Middle River MD
Originally Posted by CentralCoaster
I'm not familiar with the lt1 setup... but a pcv vent line should never be open to atmosphere on a MAF car. The pcv system needs a metered air source to suck from. If that source is closed off, you'll suck oil into it, if that source is topped with a breather, you have a vacuum leak.
So if there are no breathers, you will suck oil? If the pcv is hooked up to the intake, is that a "metered" source?
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by HeeHaw89
So if there are no breathers, you will suck oil? If the pcv is hooked up to the intake, is that a "metered" source?
Le Mans Master
Joined: Jun 2001
Posts: 6,694
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From: Less Talk, More WOT | Houston TX
Funny you post this now as some shmuck at the autoparts store the other day was trying to tell me that I would add hp if I replaced my pcv system with a breather 
Rule no. 1 don't listen to those people 
Rule no. 1 don't listen to those people
Melting Slicks
Joined: Oct 2002
Posts: 3,193
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From: Cincinnati Oh
Well you can use a breather- just be sure to plug any holes on the throttle body or intake (L98 style) to prevent a vacuum leak. I have *two* open-air style breathers - one on each valve cover - with no vacuum leaks and a normal vacuum manifold pressure. The valve covers can be open-air because it's venting crankcase gasses/pressure from blow-by and not directly connected to manifold vacuum UNLESS the PCV piping is running back into the intake manifold.
In other words, put on a breather- just make sure any holes or random tubing running into the intake or throttle body is plugged up.
In other words, put on a breather- just make sure any holes or random tubing running into the intake or throttle body is plugged up.
Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by Ramanstud
In other words, put on a breather- just make sure any holes or random tubing running into the intake or throttle body is plugged up.
This is a case where an emissions item increases performance... since pulling a slight vacuum on the crankcase helps seat the rings better. I think it has to do with reducing ring float, but I'm not sure on the details.
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Team Owner
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Originally Posted by 6spd
i also have a question about this i have a 91 L98 and i put aftermarket valve covers, i have a pvc on the drivers side and a breather. the passanger side has one breather is this okay??
No, it makes a vacuum leak, and harder for the ecm to control idle and a/f ratio.
Either run your original vent tube to the metered air in the TB, or put breathers on both sides and remove the pcv all together.
Also, the fuel cannister purge lines tie into the pcv on the L98, and those work to relieve tank pressure. If you remove this system, plug the vent lines and buy a vented gas cap
You'll have nasty gas fumes under your hood otherwise.
Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
Originally Posted by NUckINg FuTS
Would there be a problem with using a breather on the driver side valve cover only? I have a 400 sbc with a modded LT-1 intake to work on a non lt1 block (lt1intake.com). If you are fimiliar with LT-1 pcv system then you know the pcv valve mounts in the intake itself not on the driver side valve cover. The valve covers I want to buy (like most other covers) have holes on the driver side and pass side for PCV provision. I am ok with the pass side valve cover but I am left with a hole in the drivers side cover. Can I just place a breather in the hole or will that cause a vacuum leak detectable by the MAF???
If you want to continue using the PCV setup, just buy a rubber grommet plug for the driver's side hole.
Jake
Race Director
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From: The Top of Utah
Originally Posted by CentralCoaster
'Positive' comes from the fact that you're using the manifold vacuum to induce flow... rather than just leaving the crankcase open to atmosphere, as is done on the pre-smog cars.
RACE ON!!!
Last edited by CFI-EFI; Sep 14, 2004 at 10:59 AM.
Team Owner
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From: Fort Knox, KY
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On the LT1, does the PCV valve simply screw into the side of the intake or does it push in/out?
All this talk about PCV valves has reminded me to replace mine, since it hasn't been done since I've owned the car.
All this talk about PCV valves has reminded me to replace mine, since it hasn't been done since I've owned the car.
