For years, I've understood the PCV to be a circular-like system, with one side venting the crankcase OUT, and one side pulling fresh air IN. If THAT is not accurate, then someone stop me now!!!! LOL

....at the moment, my system works fine, and I have the bone stock OEM system that came stock on my L98. I was thinking about maybe adding a breather to the "in" valve cover, and without looking at the car, I can't recall which valve cover has the actual PCV valve. Then I got to thinking, since one is hooked up to the plenum, and one is hooked up to the TB, what's the difference??? Wouldn't BOTH be under vaccum, and vent OUT of the valve cover and into the TPI/Intake???

Someone help a seasoned veteran out with a newbie question!!!!!!!!!

 

if both of those are vacuum sources then something is wrong, you only need one pcv

and you need a return too

what gets sucked out of the crankcase needs to be replaced, and filtered

on the carb engines the return was ocnnected to the air cleaner and a small filter for it inside there


this is the whole principle of the pcv system and has been this way since 68 when it was first required to be used on new motor vehicles



good luck

 

The connection to the TB is above the throttle blades, so it has no vacuum. It's the source of fresh air. The reason for making the connection at the throttle body is to ensure that the air pulled in through the crankcase that will eventually make its way into the intake has been drawn through the air filter, and metered by the MAF if the car has one.

 

IIRC your car uses a MAF.

The PCV valve pulls air in from the crankcase. Note that the point at which this air enters the intake tract is DOWNSTREAM of the TB, which is of course also DOWNSTREAM of the MAF; i.e., it allows "unmetered" air into the intake manifold. "Unmetered" means it hasn't passed through the MAF, so the MAF doesn't know it's there, so the ECM doesn't either, so the ECM doesn't add fuel for it.

Note that the tube that goes from the OTHER valve cover to the TB is ALSO DOWNSTREAM of the MAF, but UPSTREAM of the throttle itself (the hole in the front of the TB at the top of the intake tube flange feeds that fitting). With that hookup, all the air that goes INTO the crankcase has passed through the MAF, so before it comes OUT through the PCV valve and into the intake, the MAF has measured it. Meaning, the MAF has seen it, and told the ECM about it, so the ECM now knows to put in fuel for it.

If you do what you are talking about, you will accomplish 2 things... neither of which is an "improvement". One, you will disrupt the MAF's metering system, and let unmetered air into the intake, which will make the car impossible to get to idle or cruise correctly, because it will be so lean; and two, those stupid "breathers" always spew oil all over the top of the valve covers and down onto the exhaust and make the car stink of burning oil under the hood 100% of the time.

I'd strongly suggest leaving it like it is, especially since there are no positive benefits to the "breather" idea, as opposed to how it is now, no matter what.

 

The PCV system on my Speed Density TBI is very similar,
and I have pondered the same question. Disconnecting the
fresh air connection from underneath the air filter, when
removing the filter, is annoying. But if wiser people (thanks
sofakingdom) make good explanation, I can learn to live
with it. Thanks guys...

 

I wasn't really sold on the breather, just kinda pondering it.....but more to the point, I was confused on exactly how it all worked on a TPI motor, which has been answered.

Thanks again guys.

 

Which large port on the TB is the proper one to connect the line to? I have a motor which i purchased and I am trying to plumb the PCV system.

 

PCV-Positive Crankcase Ventilation. All that air churned up w/ misted oil from the crankcase is pulled into the intake by vacuum to be re-mixed w/ the fuel charge and burned off. Back in the early part of the previous century you used to see crankcase breathers hanging down off mtrs and spewing all over the road. The breather in the r/s valve cover replaces and maintains air volume to the crankcase. On the TPI they happen to draw it off the the air intake at the TPS. Thats downstream of the MAF. I plugged it and am using a regular push in breather. I wanted all my intake air doing just that, going into the plenum. Joe

 

All your intake air was going into the plenum. A tiny fraction of it just got there through the crankcase. You've got the same amount of air now entering the plenum via the crankcase through the breather.

 

Apeiron, I think you're mistaken. Intake air thru the plenum mixed w/ fuel is burnt in the cylinders and out the pipe it goes. Air drawn in thru the valve cover breather maintains static presssure in the crankcase which is churned up and built up by the reciprocating mass of the crankshaft, rods and pistons. Overpressure in the crankcase is drawn off by the PCV so as not to blow gaskets and seals. What I meant was I didn't want my intake air drawn off to feed the crankcase. Stock GM routing of the crankcase intake was just to satisfy the EPA. It's part of the "closed loop" emissions circuitry.

 

Ok, so you're saying you took the PCV valve out. Your breather then is letting excess crankcase pressure bleed off, but isn't doing much to evacuate nasty vapours and condensates.

 

no, maybe we got crossed up here. The PCV is on the left side valve cover and is still in place doing it's job. The intake breather is the tube in the right side valve cover and goes up front where the TPS is. Thats the one I'm talking about.

 

That's what I thought you meant to begin with. The only difference between what you're doing, and what the factory did, is that your air coming in to the crankcase is filtered by the breather, instead of by the air cleaner. In either case, that air still ends up entering the plenum via the PCV valve.