Feedback on PCV re-routing

[tmorgan4]

I had originally planned on running the PCV lines to a catch can to simplify the lines a bit, but I was advised by a guy who knows a lot more than I do that a catch can is a waste on a "stock" NA engine. Here's what I was planning on doing instead. More colorful circles for everyone to evaluate.



Red: Plug 'em!Green: Install breather filters on. They're drawing fresh air in instead.Blue: Routed as shown.

The tube coming from the PCV valve will be run straight into the intake collector, bypassing the 2-way fitting on the block.

Any issues I'm overlooking? I know it's a simple system, but I'm new to all of this.

[T45]

It would work but you also need to put filters on the crankcase tubes coming out of the block. The ones that the red lines go to.

You're on the right track though as for eliminating it. Air enters the engine through the green, travels from the crankcase through the red lines to the valve covers and then exits the valve covers through the blue lines. Technically you can put caps on 2 of the 3 ports on each valve cover and also vent the crankcase tubes and you're done. It won't keep 100% of the dirt out and you may have some oily residue from time to time but it's all negligable.

[AlabamaDan]

If the blue are just for exiting gases, they wouldn't have to stay in place either would they?

[slamdbusa]

You may have already went past this post, but I'll update it for you.

You would be on the right track for a racecar, BUT the air that goes to the T/B would cause the emission sensors to read lean because the air isn't measured by the MAF sensor on the green circles. It is basically a air leak/boost leak type of situation.

It might not cause you any problems, but as from a driveability standpoint, it will in the long run.

[tmorgan4]

Could you elaborate a little bit further? I'm not sure I understand what you're saying.

As of right now, I've got the rear fitting on each valve cover plugged. The middle fittings have breathers, and the front fittings run into the PCV valve. The nipple on the PCV runs into the intake tube.

EDIT: Actually, I think I get it. With the stock setup, the air that comes into the valve covers (middle fittings) is monitored via the MAF and "exchanged" inside the valve covers with the air exiting the valve covers and into the intake collector.

Could you clarify why this is "OK for a race car" but not for a DD? I'm happy to hear another opinion.

[T45]

I was going to delete pcv as well but a couple things got me to thinking. A vacuum inside the crankcase would help with oil foaming if the oil ever got in contact with the crank. GSRacer just lost a bearing and that is the one thing that entered my mind.

If you are running a front sump, under acceleration the oil will want to travel to the back of the pan. If the acceleration is hard enough the sump could run low and the oil in the back of the pan could get high enough to get into the crank and get aerated. I know it's a long shot but I guess it's possilble. If aerated oil got back into the sump and then pumped through the galleys it could cause a bearing failure. Either that or the possibility of running out of oil in the sump could cause a catastrophic failure too.

I have no idea if this is logically possible but it's not impossible.

[slamdbusa]

On a DD there is more idle than balls to the wall. With a racecar the intake manifold rarely sees idle, in which vacuum makes the PCV system work correctly. The intake vacuum makes the blow-by in the engine less problematic and helping with less seal leakage and moving fresh air into the crankcase. It is an emissions thing. On a racecar the engine is at high rpm mostly which deems a PCV system useless. ( Ever watch a boost gauge go to zero when you tap the throttle? This is called equalization in the manifold, the inside pressure is the same on the outside of the manifold.) So oil catch cans and oil separators with big air lines are used to catch the oil in the vapor that the PCV would normally help dissipate. I've seen systems with a blocked PCV valve and premature seal failure is the most common problem with them. I wouldn't modify the PCV system on a DD even if it looks ugly, just not worth the headaches of poor driveability and maintenance of the seals. A good breathing engine is a happy engine, but a vacuum in the case (higher than normal) will cause poor performance.

On the issue of oil in the engine going to the rear of the pan, there are baffles in the pan anyways to keep all of the oil moving to the rear. But as the pros at the Mineral Wells told me, Overfill your oil pan by Half a quart to a full quart. KA's are known to blow up for low oil pressure, but never by tuning. They say that it doesn't matter what engine you have, low oil pressure is the number one cause of the engine failure in Drift, Drag, AutoX, etc..... Oil will always splash onto the crank there is no way to stop it, unless you have a dry sump system, so overfilling the oil will be your best bet to save your motor in any type of racing.

I hope that this helps you out.

[qsiguy]

Well, I'm running boost so my reason for modifying the system was different. I had to prevent my crankcase from becoming pressurized. Shot the dipstick out once and that was enough for me.

I had to plug the fresh air line from the air duct because it was forcing air into the crankcase. I had originally assumed I needed a catch can on it so that's what I did but as you already know it just supplies fresh air into the crankcase. Anyway I ran a hose to a homemade "catch can" but basically I just have a breather filter on it. My catch can is just PVC tube with stainless steel mesh in it so it's basically a filter. I know it does bypass the MAF but doesn't seem to effect idle that I can tell. I haven't had to take it through emissions yet so hopefully it'll pass that.

Here's a couple photos of what I did in my Q45

[slamdbusa]

Your right, turbo engine use a different setup than N/A engines. Take the SR for example, the PCV valve is located between the Intake manifold and the valve cover and the fresh air inlet is on the intake before the turbo. If boosting the VH then apply the same concept for it to too. Just move the fresh air line to before the turbo, to keep the crankcase from pressurising under boost.

On a side note, I like your custom catch can/filter. Do you have a write-up on that?

[tmorgan4]

Discussion on this topic is good. I'd just gone with it assuming it will work, and really haven't looked back since. I HAVE NOT started the engine yet. I think I understand what slamdbusa is saying, but I'm not quite sure I understand exactly what effect it will have.

It isn't going in a race car, but a 4wd that I still use the majority of the time as my daily driver. Do you anticipate I'm going to have a problem?

[slamdbusa]

I looked at a VH schematic today, and the rear line go to the block. So those lines then go to the cam covers, and they either drain oil back into the block or allow the gasses trapped in the block to take a short cut to the top of the motor. Blocking those would most like be a bad thing.

A wise mechanic told me once, "If you can tell me what this does and explain the benefit of removing it, then you can." ( He was referring to a part in a carb that he was teaching me how to rebuild, but it should apply to all things on a car. )

I hope this helps.

[tmorgan4]

Well, it's safe to say that I need to re-trace some of my steps. The fitting on the block that splits into 2-hoses, I wasn't aware that it actually went IN to the block. I thought it was just a fancy Y-fitting.

I even blew compressed air into it when it was a bare block and I swear when I plugged the other side it felt completely blocked. I really didn't realize there was a third opening into the block on the bottom of the fitting.

[tmorgan4]

slamdbusa...I can't thank you enough for bumping this topic up. I had seriously overlooked a few vital things and would have run it without ever thinking twice about them if this hadn't come up.

After spending a good amount of time looking at how the PCV setup works, what people are doing to re-route them, and the side effects of deleting it all together, I think I've come up with a new plan of action. One of my huge goals with this engine project was to simplify everything as much as possible. I know it wasn't the best engine to meet the goal, but that's besides the point.

So the PCV system is really just part of the emissions system, as an effort to reduce pollutants when cars were just freely venting into the atmosphere. I have already torn out the EGR system, and will only be running the pre-cats on the Q45 exhaust manifolds. I probably won't pass emissions as it is. Good thing we don't have them here.

Am I overlooking any drawbacks of going back to this free-venting setup besides oily residue in the engine bay and more pollutants being released? I am now thinking of just running a hose from the port that enters the crankcase on the block to somewhere in the engine bay with a breather filter. It will be able to breathe on it's own whether it's letting air escape or bringing air in.

What should I do about the vents on the valve covers? Is there any reason the valve covers need to vent? If they do need to vent, I will put one breather on each cover, and plug the other fittings. If they do not need to breathe, I will plug all 3 fittings on each side. Fitting on the intake tube will be plugged as well.

Can I PLEASE ask for come criticism on this setup.

[tmorgan4]

One more...It appears on a lot of cars the crankcase vents is through the valve cover vents. In this case, that Y fitting on the block might not go all the way through.

[Mettler]

Here's how I understood it.

Basically, crankcase pressure passes under the rocker covers through the rear fittings.

The middle two link together and have a single branch off that links up to the bend in the intake piping before the throttle body... obviously a source of pressure equalisation with what's taken from the motor, using the measured air supply.

The front fittings are linked across under the manifold to balance pressure across each bank, and also branch off to somewhere else (I couldn't be arsed looking where, that whole piping setup is diassembled at the moment... but pretty sure it's the AAC/ACV into the plenum.) I think I have no PCV valve on my motor.

Since oil vapor would exist under the rocker covers as well as the crankcase, I think it's important to leave the crankcase ventilating through them prior to exiting the motor. It obviously flows through from the back to collect the oil vapor on its way.

I theorise that having those front two plumbed to the plenum serves a dual purpose, obviously for emissions reasons, but also to generate vacuum throughout the motor to quickly suck away the oil mist.

Thus I believe the best solution may be to leave the rear lines as they are, venting from crankcase to rear of rocker covers... middle lines to be left plumbed as they are, serving as pressure exchange with the measured air supply, and the front lines to be filtered through a catch can. However, because we want vacuum in the system, plumb a hose from the original vacuum source to the catch can (this may be PCV valve on yours, or you may choose to eliminate it from the system... whatever.)

Nissan aren't silly, and obviously set it up this way for a reason. I think putting the catch can between rocker covers and plenum allows us to clean the blowby air and prevent the oil vapor getting into the intake, but also allows the engine to function as it did before, without risk of changes causing issues.

Obviously I'm repeating stuff that others have said, but trying to summarise the reasons for why things are there.

Thoughts?

[slamdbusa]

If you want to make it simple, I would leave the rear lines on or reroute them, and make a thing like GSracer did, with the middle and front lines going to a centralized breather. As long as it gets good venting, and check it for oil collection, you should be good enough there.

I would use big line like -8 or -10 line to bypass the PCV system to a centralized breathing tank just to be safe. Built up pressure is bad and as long as you can get rid of the pressure it should be okay. Deleting the system and capping it off is not a good choice.

On the rear lines the part that goes to the block may be clogged with sludge. It may have an orifice that is part of a metering system, I don't know. On a reference with an SR, there are metering orifices in the emissions system in the lines to and from the stock oil catch can, so I believe that there are in this engine too.

For the best bet, I wouldn't change anything on the routing on the PCV system on a DD, But if you want to, make sure you use big enough line to ensure it breathes.

[tmorgan4]

In all honesty, I really just want to go back to the stock setup. Someone on here advised me to do it the way I have it now and I wish I hadn't. Those rear fittings have already been removed, the holes filled, and they look like they were never even there.

If I want to modify it, I have to pull the plenum and valve covers back off which I really don't want to do now that the engine is finally installed.

I did read about one setup where a guy installed a vaccum pump to suck the oil mist out of the crankcase, but I don't understand how this would work in the case where the crankcase is actually sucking air back in.

[qsiguy]

...On a side note, I like your custom catch can/filter. Do you have a write-up on that?

No write up for it. It's just a PVC nipple, 2" I think, with two 1/4" MNPT by 5/8" hose barb fittings. Screw on PVC caps on the ends with stainless steel mesh inside to collect any vapors. In this case it's basically just an air filter as nothing will ever come out of the hose. The hose barb on top was intended to be ran down to the ground in case any oil vapors came out. Again, in my case it's just sucking air in all the time unless I'm wide open or in a boost condition.

...I don't understand how this would work in the case where the crankcase is actually sucking air back in.

The only reason there is air being sucked into the crankcase (via green tubes in the first graphic) is because with the PCV system intact the high vacuum in the plenum is drawing it in to mix fresh metered air with the crankcase vapors. If the PCV system has been modified or removed there may not be air being sucked in any longer. If you ran the "blue" hoses to catch can, leave the red to equalize pressure(?), cap the "green" hose or also route to the catch can, any positive pressure will just vent out through the catch can.
Modified by qsiguy at 3:50 PM 1/7/2008

[T45]

Don't sweat it Tyler, it's really no big deal that's going to destroy your engine. Just vent all lines to the atmosphere and you'll be good. That's the way all engines were until emissions stuff started. They are just there to relieve pressure that will build up in the engine as the air inside heats up and expands. There's really no air exchange other than that and you'll probably not even have the oily mist we speak of unless you have ring blowby.

I believe the Y in the rear of the block is to vent the crankcase itself as the only way for air to get in is through the oil return galleys. Maybe the engineers didn't think it would be good to rely on just those alone for total venting?

[slamdbusa]

I believe the Y in the rear of the block is to vent the crankcase itself as the only way for air to get in is through the oil return galleys. Maybe the engineers didn't think it would be good to rely on just those alone for total venting?

The Y fitting is for the top part of the block that is higher than the oil return passages in the head. There are passages in the head and block that return the oil that is used to lubricate the cams, lifters, etc.. the vapors can travel through those, but not as easily as the red lines could.

[tmorgan4]

Don't sweat it Tyler, it's really no big deal that's going to destroy your engine. Just vent all lines to the atmosphere and you'll be good. That's the way all engines were until emissions stuff started. They are just there to relieve pressure that will build up in the engine as the air inside heats up and expands. There's really no air exchange other than that and you'll probably not even have the oily mist we speak of unless you have ring blowby.

I believe the Y in the rear of the block is to vent the crankcase itself as the only way for air to get in is through the oil return galleys. Maybe the engineers didn't think it would be good to rely on just those alone for total venting?

That's EXACTLY what I was wanting to hear. I'm going to do my best to get a good ring seal right away and hopefully won't have to deal with oil all over the engine bay.

Do we have a group consensus on whether or not that Y-fitting in the rear of the valley on the block actually protrudes INTO the crankcase? I need to make sure and plug it up if it does, but I swear mine didn't go through unless it was plugged as mentioned.

[Mettler]

Do we have a group consensus on whether or not that Y-fitting in the rear of the valley on the block actually protrudes INTO the crankcase?

Basically, crankcase pressure passes under the rocker covers through the rear fittings.

It does, I have a bare block here that I've thoroughly studied and inspected to see how the whole oiling and breathing system works.

Also, it doesn't protrude into the crankcase, as there is a big vertical hole bored straight through the back of the block from top to bottom, into the crankcase. That mild steel Y fitting has simply been press fit into that hole.

But yes, that's where crankcase air/pressure is ventilated through into the rocker covers... 100% definite, confirmed, myth busted.

If you like, I can photograph the crap out of my bare block when I pull it out and post all the pics up with a writeup, so you get a better idea of how the block's internal systems work.

Here's the most handy pic I could find for now to demonstrate:

[Mettler]

I just went over to the car and photographed under the crankcase to clarify things:

Car in workshop with dummy block & heads fitted for fabrication purposes:

View from underneath, clearly showing crankcase ventilation at the back of the motor... this hole is what goes up to the Y piece:

[tmorgan4]

Thank you Mettler. Nice shop too!

Not exactly what I wanted to hear, but I'd rather fix it now than when I start it for the first time. I hope I don't have to pull the plenum off again, but it's going to be tight under there.

I still don't understand whether both the crankcase AND valve-covers need to vent, or just one of the above? I'm going to plug as many ports as I can be safe doing and vent the fittings I need.

[npez]

Didn't see this in this thread, but as I'm redoing some of my PCV plumbing I'd like to find out what the size/thread pitch is on the tee fitting where the PCV valve screws into.

Does anyone have this info? As I'm cutting the "gooseneck" off of the coolant pipe I will need to purchase a replacement tee to re-do that functionallity.

Please advise.

Thanks,Nick.

[tmorgan4]

I have a new PCV valve sitting somewhere in my 10,000 parts. But...If you're replacing the entire piece, what about going with with a PCV valve with a more common thread. The stock one might not be hard to find, but it doesn't seem like there's any reason to stick with it if it's going to cause difficulties.

[npez]

I have a new PCV valve sitting somewhere in my 10,000 parts. But...If you're replacing the entire piece, what about going with with a PCV valve with a more common thread. The stock one might not be hard to find, but it doesn't seem like there's any reason to stick with it if it's going to cause difficulties.

Great suggestion - I hadn't thought of that. I think I'll just get a PCV from summit and plumb it in.

Thanks Tyler.

Nick.

[SuperHatch]

Great suggestion - I hadn't thought of that. I think I'll just get a PCV from summit and plumb it in.

Thanks Tyler.

Nick.

You can also just cut the PCV valve T off of the gooseneck and reuse it.

[craigztoyz]

If you pull the upper. you can plumb it nicely underneth, andtake out feet of it. Mine looks a lot cleaner, better when the ss braided lines get here.

Easy to redo, as it is very basic.

[npez]

Thanks everyone for your suggestions. I'll take a look at what option will work best/cleanest as I'm keeping this system intact (i.e. not plugging anything up), the only thing I'm changing is running the fresh air ports to somewhere else so it's ready for when I put the boost on - similar to Shane's (gsiguy) issue with pressurization.

Thanks again,Nick.