PCV system - modification options

I looked but didn't see any dedicated thread on this. The focus of this thread are: How exactly does the PCV system work on an unmodified 3800 S/C, What can be done to overcome issues like blocked passageways due to other modifications like throttle bodies and intercoolers, and what can we do to improve the PCV system?

PCV function

Just to start out, the PCV system does one thing. It allows the crankcase vapors produced to be circulated and extracted from the crankcase in controlled currents within a closed circuit. The PCV circuit is very simple. What makes it seem confusing is its spacial configuration.


Here's a diagram of the PCV circuit flow.


Here's another I made for the sake of understanding the PCV circuit.
Under typical driving conditions, that is what's going on.


Here's what starts to happen when the intake manifold is in ambient pressure and more so with boost. The PCV valve bleeds the pressure some but there's probably almost as much air going backwards through the inlet side into the intake again. Many people that have turbo cars actually put another oil catch can at that spot to manage the vapors on both sides of the circuit since you have two vulnerable spots.

I'll add more later.

PCV circuit obstructions

There's a few common modifications that can obstruct the PCV circuit and if you don't do something about it, the crank case will be basically air-tight, that is until something lets go. That would cause things like oil starvation, sludge buildup, etc. What you would likely notice right away on this motor is the high-pitched noise and an intake gasket or oil seal busting in a hurry.

The modifications that block the circuit are:
*some throttle body adapters - blocks the PCV inlet on gen III superchargers
*some intercooler cores - blocks the passageway between the supercharger and the lower intake in one or two places

Basically, this issue can be overcome by either reconnecting the blocked area by adding a new passage for it either externally or internally, or use a breather. The breather is going to virtually eliminate the PCV system and simply give the crankcase a free two-way path to the atmosphere. Something else to understand is that you can have slightly different things going on depending on exactly where the blockage is in the PCV circuit. For example, if you have the PCV inlet blocked off on a gen III blower because of a throttle body adapter, you have a totally sealed crank case at idle (bad) but under boost, the PCV valve is actually opening slightly and letting air bleed out of the crank case into the intake manifold. In this case, if you use a breather, your PCV valve actually still works like stock. On the other hand, if you are running an intercooler core that blocks both passages between the blower and the lower intake manifold (my WBS gen V core does this) and then you add a breather, your crankcase will be safe with a breather but the PCV valve will not work at all. The point is you want to be aware of exactly what is going on before you mess with it.

The breather idea is the safe and simple way but definitely not ideal for a couple reasons. Firstly, if you refer back to the diagram I drew, you can see the PCV inlet is situated after the maf sensor so that tells you the PCV airflow is metered air. By using a breather and making no other changes, you are introducing unmetered air to the engine's intake which will throw off the tune (mostly during idle) a tiny bit. It's not a big deal but something to consider, especially if you're really trying to tweak your tune in. The other concern with running a breather in place of a closed PCV system is that you're just keeping the crank case at pretty much atmospheric pressure under all conditions. It's better to have a slight vacuum in the crank case in order to do a better job of evacuating these vapors more quickly and reduce oil foaming and sludge buildup. The PCV valve does the job of maintaining this ideal crank case pressure. Another issue to note is that a breather is not necessarily emissions compliant since it's just going to be throwing crank case vapors (hydrocarbons, etc) into the atmosphere any time you're in boost.

Improving the PCV system

The PCV system has the inherent problem of circulating oil vapors from the crank case into the engine's air intake. This sucks for a few different reasons. Oil accumulates all over the intake tract and dirties things up. If you have an intercooler, this oil also builds on the core fins making it more restrictive and less affective in cooling. A bigger problem is that once oil gets into the combustion chambers, it acts like a very low octane fuel potentially causing spontaneous detonation, and can cause hot spots which causes the same problem.

There is a lot on the internet and a lot of opinions about how you can improve the PCV system for high performance engines but for now, I just want to get to reducing the oil consumption as it is indisputably bad. The most popular way to try to control the amount of oil getting into the intake via the PCV system is using an oil-separator aka an oil catch can. These can be purchased from lots of different places but basically it's a small canister that connects in-line with your PCV circuit and it condenses the PCV air so that the oil collects at the bottom and the cleaner air moves on to the engine's intake. The design varies from product to product but the better ones usually have media baffles to pick up the oil better. IMO a bigger can is better and the cooler it stays, the better. Since a catch can is basically a resovoir collecting oil all the time, you have to drain it from time to time. I would imagine this additional maintenance, although easy, might be one reason why most cars don't have PCV oil separators from the factory.


Here's my diagram modified with a catch can. If you actually do this on your car, it is a bit trickier to do than the diagram makes it out to be because of the location of the PCV valve on the 3800. It all depends on your setup though.

Just posting one option for a PCV can location

This is where I'm putting mine.
I got this one.





You can see it but it really doesn't stick out at all and it's super easy to get to the drain plug or remove it for rear spark plug changes and stuff. It's also in a relatively cool area which is a good thing for the oil condensation happening in the can.


In this picture, you can see how the catch can is being connected to the engine. The hose in the picture is sitting on the LIM fitting and the other fitting on the s/c is not connected. Also that might be another mounting option for someone that's running a genV and no EGR but I haven't 100% checked fitment. The bracket is mounted to the EVAP port.

X-post from my showroom since its related info and will show up in searches here.

The PCV breather is pretty interesting. I wanted something to keep the oil vapor out of the intake and also wanted something that can bolt right into the stock location. My prototype is made with Delrin and works very very well. Basically, it replaces the normal PCV cover, and routes out a line out to a filter/catch-can and then back in again.

Here we see the new cap. The next version I think I would have the hose barb both facing to the right. I did it on both sides at first because I was going to have the catch can in the middle at the back, but then decided that an oil can right over the rear exhaust manifolds might not be the best way to do things. So i moved it to the side.

The underside has a machined nub for the bit of hose that connects to the outlet of the PCV valve. Clearances make this almost touching the valve when the spring is fully compressed.

The whole assembly looks like this. The hose slides a bit tighter when the spring compresses and the cap is screwed down.

A wee bit of cutout gasket maker, with the PCV in and hose on it.

And the whole assembly. Eventually I'll change the clear tubing to some nice thick black vacuum line.

It actually intercepts a good amount of oil. There is almost a 1/4" of oil in the filter. I've done one 2 hour drive, and maybe 4 in town trips since installing.(usually pretty spirited driving..well ok, tons of WOT..)

Overall I'm thrilled with the results. It bolts right in, and does its job. I might do a future version with the barbs both facing the same direction, no plug in the top, and do some nicer chamfering on the edges. This was really just a quick prototype. So who else wants one? They only take a couple of hours to make.

ME WANT 1! Let me know when your ready to ship/sell.

I'll make you one next time I'm back at the machine shop. Probably within a few weeks. You supply your own oil filter/separator and barbs. I'll tap the Delrin for 1/8" NPT. Personally I'm using 1/8"NPT thread-to-1/4" barbs and 1/4" ID hose. Runs well with no strange sucking or whistling sounds.

I'm thinking this one will look like above, but with no brass top plug, hose barbs both facing to the right, nicer finishing of the machining, and proper bolt counter-sinks.

You will probably want to make some kind of gasket, or just RTV. Also depending on what oil separator you use, you might have to plug off the bottom drain. You're on you own for that part. And don't torque the cap too tight, since Delrin is a softer composite and will dent a bit.

Its yours for the price of shipping.

Sounds like a bargain to me!

So I have an update on my PCV modification.

3 months with it on, usually driving 20 minutes a day, in-town, lots of hooning, and WOT.

Picked up about 1/3 of the canister. o_0



I have nothing to compare it to, but I've read that on other engines that are under boost people are always very surprised how much gets picked up. Its also not too inconceivable that an engine with as many miles, years, and boost as mine would be experiencing blow-by.



What was also interesting is the "stuff." Not really oil, not water, not dirt, but all at the same time. You could see layers where the different densities have settled over the time there.






It smells like oil, engine grime, wd40, and dirt. Weird stuff, I played with it a bit, even the thick mud parts I couldn't get to mix with water. The light top liquid also wouldn't bind with water, which is good I guess. I've never had this kind of mud come out in an oil change or anything, so maybe normally it gets burned up. IMO, best to intercept it.

I guess I should do a compression and leak-down test next summer when it comes back out of storage. ... and maybe try a catch can on the 98 to see how it compares.

Overall, got to say, I'm glad I put it in.

nice update. That's nasty looking stuff!

Ok check this out. I installed my PCV catch can on 1/16. On 1/31, 372mi later I drained 5/8oz of fluid from the can. It's not very much but something. Here's what's getting me though. I was expecting to see something like what Andrew did but mine pretty much looks exactly like brake fluid - nearly clear with the same consistency. It smells like exhaust gas. What do y'all make of that? My setup is a little different then Andrews but I don't see what would make that kind of difference.

turtleman wrote:

Ok check this out. I installed my PCV catch can on 1/16. On 1/31, 372mi later I drained 5/8oz of fluid from the can. It's not very much but something. Here's what's getting me though. I was expecting to see something like what Andrew did but mine pretty much looks exactly like brake fluid - nearly clear with the same consistency. It smells like exhaust gas. What do y'all make of that? My setup is a little different then Andrews but I don't see what would make that kind of difference.

Yours is just condensed oil fumes, no water/antifreeze from any head leak.

Just an update on my catch can. A while ago I replaced a failed FPR, and ever since the catch can fills very slowly.(Which is good.) The bad FPR was sucking a good amount of gas in the vac line, so I guess that explains extra goop with teh bad FPR. So if you find you have a can that fills rather fast, give that vac line under the FPR a sniff.

Great post, Turtle.

I was thinking... Looking at Turts pics at the top, if you were able to stick a vacuum regulator in the line from between the TB / MAF to the crankcase... set it to 5-10 PSI.... that would effectively give you a way to suck a slight vac on your crankcase whilst still maintaining the PCV. Slight crank vac has a few benefits such as less oil splashing and improved piston sealing.

Thoughts?

That's pretty gnarly stuff. Naturally, it makes sense to catch it and keep track of it, but it is possible that it could actually serve as a lubricant? Ideally,should their be no liquids at all entering though the PCV or is a trace of moisture healthy?

This seems like the place to put this...

I just bought a gen V, and I'm taking it all apart to clean it really good, and the PCV was covered with a weird milky oil when I pulled it out. Is that normal?

To an extent, it's completely normal. That's just aerated oil that's made it through the system. That's one of the main reasons you should install a breather (or form of) on the oil cap when you drop a few pulley sizes and mod. The stock PCV system can't keep up with the extra boost. What you're seeing is normal. Much more of that, and the PCV becomes clogged, and you start blowing oil back into the engine.

Cool. Considering the function of the pcv I assumed it was ok, but I wanted to be sure. I just don't like the idea of blowing oil through my supercharger.