Build Thread My Never Ending 89 Notch Thread

84Ttop said:

Sorry if this is sort of a Hijack Jeff:
@Noobz347 I'm really not following your theory on the must have a working pcv system. The mass air meters the air coming into the engine for combustion purposes. The combustion process happens and most of the gasses are expelled out of the exhaust system. Windage and poor ring seal can lead to crank case pressure. The air that is vented from the crank case doesn't need to be metered or recirculated. From the oe perspective the pcv system provides a more positive ring seal, this is great to a point where the motor is tired and/or fed with forced induction, at that point you start to see oil being pulled from the crank case and we all know that oil doesn't like to burn like the air/fuel mixture that typically feeds the motor. Running vented breathers or a catch can yield the same result and as you said provide a larger pathway for those gases to escape. I have had more cars that I can count with open breathers in the valve covers and the pcv system plugged and have had zero tuning issues or problems otherwise. It just all doesn't add up for me.

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A portion of the idea is that air vented from the crank case is ALREADY metered. Venting those gases does a couple of things:

It is metered air that is unused for combustion. In a nut shell, that air that is allowed to vent to atmosphere is replaced by metered air entering through the meter. So you end up measuring essentially the same air twice. The escaping air is never seen mixed in with the rest of the exhaust as it passes over the 02 sensors. The EEC is going to try and compensate for that slightly richer exhaust gas. In itself, this not a huge amount of air to allow to escape but it does loosen up on your tune characteristics and cannot be relied upon to be constant.

On a street car: Having the ability to vent crank case gasses in some sort of uniform flow, removes moisture, partially spent gasses, and corrosive elements in the crank case mixture. Having a vent that is two-way does not allow this straight-shot kind of removal. Areas within the block might see a very lengthy removal of these gases while some see little or none at all. Not an issue for a drag car really. They don't generally see the heat cycles and soak, elevation changes, number of start cycles, or weather and air changes, that a boosted DD might see. Oil is likely changed after each event.

Allowing air to be pulled from the breather: If there's no one-way check valve on the breather then this is the worst part of having a breather. Un-metered pulled into the engine is not consistent. It changes at various power levels (of course) but is also not consistent between a cold motor, a hot motor, or one that is right in the middle (good) and heat soaked. For someone who religiously changes their oil, this is probably the worst characteristic of a breather. I once upon a time ran a breather on mine but noticed drivability issues. WOT throttle runs were picture perfect though (very pretty data log). Keep in mind that the breather was installed at the time of tuning and that several rolls on the dyno were for drivability and differing power levels. Also keep in mind that O2 sensor data is discarded at WOT and exhausted gases are not measured in any way. Predetermined fuel tables are also used and there no adjustment other than baro index at startup. Intake temp readings are used for adjusting only timing. One thing led to another and eventually led me to closing off the breather (I'm at the "for chits and grins" level of troubleshooting by this point). Low and behold...

Somewhere on this site, are several old posts created by @vristang . They are threads specifically related to the PCV system on Fox cars. It was one of these threads that guided me to my solution and brought me to Stangnet. The more I read and researched, the more sense it all made to me and ultimately, led me to fix my problem.

Since that time, I've run into various Mustang Folk that get to talking about cars and eventually issues. At last count, this same concept has restored 3 boosted Fox bodies to well mannered streetability. Two of those cars obtained their breathers in the same way that I got mine.... From the shop that did the tune.

Admittedly, the last car was a slightly different case because it had issues besides just a breather.

Edit:
Added two lines above.

84Ttop said:

I can see where adding an open breather to an otherwise working pcv system could introduce unmetered air but I fail to see where a car with no pcv system and open breathers is utilizing unmetered air?

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I don't know that it necessarily does. What I would prefer NOT to have in that scenario, is valve cover/crank case gasses (previously metered air) escape unaccounted for.

I would also like to have (on a street vehicle) the constant removal of that mix of burnt gasses and atomized oil burn-off, removed from those areas and not suspended in my oil or deposited on the interior of my block.