Good write up.
Had to bump this old thread because other cars have a few vents on the motor. Normally blow by comes from the crank vent which leads to the PCV valve since most the pressure comes from there and the PCV needs to open and close depending on the throttle %. But there are vents on the valve covers too. I'm not familiar with this motor yet but it looks like you caught the valve vents. Where is the crank vent with the PCV?
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Originally Posted by wstar
(3) Why doesn't Nissan install a catch can from the factory, thus meeting EPA *and* not putting dirty oil vapors into the intake? Because you usually have to empty a catch can even more often than you change oil, and if you let it go too long and fill up, the liquid oil will get sucked into your intake via vacuum while the car's running, and that's *really* bad. Most people have a hard time even changing their oil on time, there's no way a consumer car can have catch cans from the factory. They'll just fill up and dump into the engine anyways, possibly catastrophically. Keep in mind cornering/braking/accel G-forces will make the fluid in the can crawl up the walls. You have to keep the level low enough to not walk up to the vacuum line and get sucked in as liquid. Good can design can help with those problems.
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That's why you need a AOS. A air oil separator needs to be installed and then routed back to the block. On subis Crawfords AOS does this. Whatever pukes out the 2 valve vents or crank vent, goes into the AOS, is separated, and then drains back to the crank vent via a TEE or Y connector. This way in a race like around VIR the motor won't be down on oil.
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Originally Posted by spearfish25
Can you just run the lines to a point under the car and just let the overflow oil and vapors drip/flow out? I don't give a **** if the EPA doesn't like it. Would be simpler than the cans.
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I've done it on a subi. A few hard turns made me stop it since the motors sit sideways and the valve vents puked oil everywhere.
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Originally Posted by sixpax
You would get a CEL and a crappy idle if you ran it open like that.
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No you wouldn't, not as long as the intake manifold return ports are capped off. The vents are not metered air.
Quote:
Originally Posted by wstar
I don't think it would give a CEL really. You'd block off the PCV lines on the intake and vacuum sides (so no vacuum or intake path peaks for CELs), and run the lines from the valve covers to open air (probably with a simple filter). People do it on older V8's all the time (you see those tiny air filters they mount on the valve cover, that's their "PCV" straight to air). It would serve the basic purpose of not letting excess pressure build in the crankcase, and it would filter any air that was drawn inwards under conditions where the crankcase pressure goes negative. There are probably some subtle points being missed though (if nothing else, it might still be nice to have a pair of them with opposing one-ways so that you get some fresh-air exchange). I wouldn't recommend it just for all the subtle unknowns.
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Youre correct. Only thing I'm not sure of though is when the lines are hooked up to the mani, its providing a sucking action so it pulls the blow by out of the block and valve covers. By letting the air just come out as pressure builds might effect the motor since its not getting "helped" out. I did run the vents to atmos before on a subi with no issues but you never know long term I guess.
That's why a AOS routed back to the mani is king!! Oil gets caught and sent back where it should be, clean air gets separated and put into the mani for no loss or power or sludge build up and you don't smell oil blow by fumes that venting to atmos will produce, and the intake still provides a vacuum on the block and valve covers to keep everything working like OEM.