Oil cap breather
Oil cap breather I have a catch can and now i have a oil cap breather as well! Very nice piece. Just wanted to clean up the looks and release crankcase pressure issues as well. This piece is made great! Very nice!! Has a 1 way check valve as well!
Joined: Aug 2007
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From: Turnin' Wrenches Infractions: 005
When you have a closed PCV system/crankcase there is a certain amount of air that is circulated into the intake through vacuum and burned through combustion. That air is accounted for in the tune. When you change the amount, say by adding a straight breather on a valve cover, it alters the amount of air in the intake (aside from whats coming through the TB) and changes your air fuel ratio. Since its not known, the pcm tries to compensate but in the end you will get symptoms similar to an intake leak. If you tune the car to account for it thats fine, no issue. But most people dont have access to tuning software to make that change when they add a breather. A one way valve lets pressure out if needed but no fresh air in. I'm running a GM vented cap that works on the same principle, releases pressure but does not let air flow back and forth.
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Joined: Aug 2007
Posts: 24,241
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From: Turnin' Wrenches Infractions: 005
Yeah that thing is slick looking. The gm part number can be found by searching vented oil cap here and several threads pop up. It looks almost like a stock cap. It was actually designed for the smaller engines where up north the pcv system can freeze up. Installing it gives a pressure relief when needed. It fits our cars perfect.
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Verdad Gallardo When you have a closed PCV system/crankcase there is a certain amount of air that is circulated into the intake through vacuum and burned through combustion. That air is accounted for in the tune. When you change the amount, say by adding a straight breather on a valve cover, it alters the amount of air in the intake (aside from whats coming through the TB) and changes your air fuel ratio. Since its not known, the pcm tries to compensate but in the end you will get symptoms similar to an intake leak. If you tune the car to account for it thats fine, no issue. But most people dont have access to tuning software to make that change when they add a breather. A one way valve lets pressure out if needed but no fresh air in. I'm running a GM vented cap that works on the same principle, releases pressure but does not let air flow back and forth.
keep in mind there is an fresh air source tied to the air filter tract that feeds the crank case. This is the metered equivalent of any 2-way breather on the engine, which is why I asked what was the point of the check valve? If we have an intact PCV system , this tube functions to release pressure, exactly like the port that was just added to the oil fill cap... so now he has two I guess. "shrug"
Joined: Aug 2007
Posts: 24,241
Likes: 89
From: Turnin' Wrenches Infractions: 005
I wouldn't try to change the tune to account for un-metered air, fwiw, if the car is a MAF sensor style. IF there is map sensor, it would not notice the difference. So in both cases, there is no need/desire to alter the tune.
keep in mind there is an fresh air source tied to the air filter tract that feeds the crank case. This is the metered equivalent of any 2-way breather on the engine, which is why I asked what was the point of the check valve? If we have an intact PCV system , this tube functions to release pressure, exactly like the port that was just added to the oil fill cap... so now he has two I guess. "shrug"
keep in mind there is an fresh air source tied to the air filter tract that feeds the crank case. This is the metered equivalent of any 2-way breather on the engine, which is why I asked what was the point of the check valve? If we have an intact PCV system , this tube functions to release pressure, exactly like the port that was just added to the oil fill cap... so now he has two I guess. "shrug"
Staging Lane
Joined: Aug 2016
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From: Florida
I emailed them to see about a tracking number, and he got back to me saying that he wanted to double check with me first before sending the unit off because the breather doesn't fit gen I SBC oil breathers because that's what he assumed was in my car (You fill out a little info on your engine/car combo at check-out) so hopefully it gets sent out soon. I guess its good that they want to make sure the fitment works, but now I won't get it this weekend :/
And thats just it, its unmetered air, just like and intake leak. The maf cannot see this air because its injected at the neck of the intake after the maf. It will alter the afr. Enough to require a tune/cause irratic running? Maybe not, but that doesnt mean you shouldnt be aware of it.
Think of this. The brake booster is "un-metered air". Next time you get into a maf car, pump the brake at the light, watch the wideband go lean. There is always going to be some un metered air in a system like this on an automobile. I was only pointing out that... before he added the breather to the oil cap... the engine already has one that routes the crankcase -> air filter tract. So now he has two. Which is why I says "What da point brah"
Joined: Aug 2007
Posts: 24,241
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From: Turnin' Wrenches Infractions: 005
Well to me the air coming from the crankcase should correspond to rpm and load, I.e. the VE table, so you are actually accounting for it during tuning because I consider it predictable to the engine running under various conditions which correspond to the table you are tuning. The brake booster, well theres nothing you can do about that since its on and off, however its not gonna be on under throttle so whatever it is, is steady.
right, my post says, to try not to tune around it. the un-metered air is random. At low pressure (near wot) it will be negligible and during high vacuum situation it will be significant if the PCV valve and tubes are all intact.
Think of this. The brake booster is "un-metered air". Next time you get into a maf car, pump the brake at the light, watch the wideband go lean. There is always going to be some un metered air in a system like this on an automobile. I was only pointing out that... before he added the breather to the oil cap... the engine already has one that routes the crankcase -> air filter tract. So now he has two. Which is why I says "What da point brah"
Think of this. The brake booster is "un-metered air". Next time you get into a maf car, pump the brake at the light, watch the wideband go lean. There is always going to be some un metered air in a system like this on an automobile. I was only pointing out that... before he added the breather to the oil cap... the engine already has one that routes the crankcase -> air filter tract. So now he has two. Which is why I says "What da point brah"
The brake system is closed and uses available excess vacuum and provides no source for additional airflow. If you go lean standing on the brakes, you've got blown seals in your booster.
A valve cover breather on a mass airflow car does give the opportunity for extra unmetered air, but only when the PCV valve is open. And it's a tiny percentage of very predictable airflow. It is not random. It will provide the same amount of additional air on a RPM/KPA basis. Any tune will compensate for it without issue. Especially a speed density tune.
Also, the stock system uses a source of filtered, metered air post MAF. There is no unmetered air in a stock system.
Everything you just said is wrong. Again.
