PCV system. Do I need it now?
Originally Posted by TheBlurLS1
Are those eyes directed towards me? How does any of the information in your post help/correct any of the information in mine? I'm pretty sure me saying what I said about "sucking fresh air into the motor" was the exact same you decided to post again. 
Originally Posted by TheBlurLS1
Are those eyes directed towards me? How does any of the information in your post help/correct any of the information in mine? I'm pretty sure me saying what I said about "sucking fresh air into the motor" was the exact same you decided to post again.
no, they wernt directed towards you.... i quoted you because you're the only one in the thread that said it correctly..
the rolleyes was directed toward the "most people" that follow the racecar "logic"...
Originally Posted by 98Z28CobraKiller
I still don't understand how the PCV could "suck" anything if it is under pressure.
its not under pressure. it takes only a small vent to equalize the pressure created under most circumstances.
it works like this:
lets pretend the crankcase is totally sealed except for two ports.. one from the throttlebody and one to the PCV/intake.
when air is sucked, thru engine vacuum, into the intake, fresh air is pulled into the motor from the throttlebody side.
since under normal driving, you have vacuum, you get this pull constantly... this pulls fresh, filtered air into the motor, and displaces the blowby gasses that would otherwise build in the crankcase.
if left unchecked the gasses would condense in the oil, but since they're constantly replaced with fresh air, it doesnt condense and build. so your oil lasts a reasonable length of time.
now at wide open throttle, there is no vacuum.however you have two 3/8" ports that can easily flow any access pressure out... fresh air is not being pulled into the motor... but the second you let off the throttle, theres a vacuum and its being pulled again.
the only system that creates a vacuum at WOT uses a pump, like a vaccum pump or some dry sump systems..
gasses are pulled out of the crankcase, not pushed...the fresh air vent is there to regualte system pressure...if the crankcase was totally sealed the pvc system would pull the seals out of the motor...the valve itself acts as a check valve to allow gasses in one flow direction only
One thing most people fail to notice is that the "fresh air tube" is on the 14.7psi side of the throttle body, and is ALWAYS under 14.7psi at normal driving. The PCV tube is on the "less than 14.7psi" side of the throttle body. This pressure differential is what allows fresh air into the crankcase.
This "less than 14.7psi" is because of the vacuum the cylinders are pulling on the manifold, this is obvious.
If the rings let more combustion gasses into the motor than the PCV is flowing into the manifold, and the crankcase pressure rises to over 14.7psi, then you have a problem. The freshair tube will no longer be able to "suck" in fresh air due to there being not enough atmospheric pressure to "push" it in.
This is what is meant by "the PCV can't keep up".
This "less than 14.7psi" is because of the vacuum the cylinders are pulling on the manifold, this is obvious.
If the rings let more combustion gasses into the motor than the PCV is flowing into the manifold, and the crankcase pressure rises to over 14.7psi, then you have a problem. The freshair tube will no longer be able to "suck" in fresh air due to there being not enough atmospheric pressure to "push" it in.
This is what is meant by "the PCV can't keep up".
The "fresh air" tube is the one that goes from the tb to the passenger valve cover, right? If I understand correctly, you are saying that if I remove that tube from the tb and put my finger over it (the tube not the tb nipple), I would feel vaccuum there at idle? And when at WOT it would "blow" air out?
The part that I don't get is that the manifold is always "sucking" or trying to suck air at WOT or otherwise. How is it that fresh air would escape the vaccuum and flow in the opposite direction regardless of throttle position?
I can't wait till the light bulb comes on. Please dumb it down for me.
The part that I don't get is that the manifold is always "sucking" or trying to suck air at WOT or otherwise. How is it that fresh air would escape the vaccuum and flow in the opposite direction regardless of throttle position?
I can't wait till the light bulb comes on. Please dumb it down for me.
Originally Posted by oange ss
yes, depending on how well sealed your PVC system is sealed yes....no.....fresh air intake not exhaust, PCV is used to vent blowby gasses into the air vacuum stream
Huh?
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I got rid of my PCV and installed 2 Metco breathers (one on each valve cover). I have ~100 miles on the setup with no issues yet. Absolutely 0 oil in my ported FAST 90, that is a huge plus.
Originally Posted by 98Z28CobraKiller
The "fresh air" tube is the one that goes from the tb to the passenger valve cover, right? If I understand correctly, you are saying that if I remove that tube from the tb and put my finger over it (the tube not the tb nipple), I would feel vaccuum there at idle? And when at WOT it would "blow" air out?
The part that I don't get is that the manifold is always "sucking" or trying to suck air at WOT or otherwise. How is it that fresh air would escape the vaccuum and flow in the opposite direction regardless of throttle position?
I can't wait till the light bulb comes on. Please dumb it down for me.
The part that I don't get is that the manifold is always "sucking" or trying to suck air at WOT or otherwise. How is it that fresh air would escape the vaccuum and flow in the opposite direction regardless of throttle position?
I can't wait till the light bulb comes on. Please dumb it down for me.
Now, at WOT, you're bound to be blowing gasses through the "fresh air tube" because you're producing much more blowby than at idle. If you barely feel any suction from the freshair tube at idle, imagine how little the amount of extra blowby needs to be to overcome it. At 6000rpms, there should be plenty to do just that.
This gas coming through fresh air tube has NOT passed through the catchan. I've been kicking around the idea of putting a PCV valve in that line to serve as a check valve, this would force the gasses to all go through the catchcan and into the manifold.
Originally Posted by King James
Okay, so with a catch can and the LS6 PCV mod which is the best way to hook everything up? What exactly should be plugged?
Run the LS6 valley cover to the catchcan, then from the catchcan to the intake manifold.
