OK… yes this thread has been DEAD for over a yea but i am bringing it back because i am about to re-do my pcv & vc situation…

Currently on my ka-t i have my PCV disconnected from my intake manifold… The intake manifold ports has been sealed shut. The pcv is just sitting in that oil / air separator box attached to the block in CLOSED mode because there is NO vacuum to pull it open. So now at idle, cruise & boost, all the crankcase gas or whatever you want to call it is escaping thru the valve cover breather.. I have a 5/8 hose attached to the VC and running to a glass bottle as my ghetto catch can.. Clear oil does come out but once it sits in that bottle it turns into a milkshake guessing from the E85 fuel that its mixing with… But the oil in my OIL pan is clean as can be…

The stock ka system is designed to have fresh air enter thru the VC and exit thru the PCV… When i was NA, and when the PCV was connected properly, i could place my finger by the VC and feel it sucking in air… because the intake manifold was sucking out the crankcase gas via PCV… So it only made sense that since the PCV was the exit door, the VC was the intake side… For a while i left that VC VTA and NEVER had any oil come out… But eventually hooked it back to the intake…

Then went turbo… Left the stock PCV setup functional… Worked good while at idle and cruise until i went into boost… At that time thats when i started to get oil shooting out the VC … WHY..?? My guess is that the Boost closed off the PCV leaving the crankcase gas only one exit.. which happened to be the VC… Thats when i put my ghetto glass bottle on the VC to catch the oil…

Later i removed the PCV due to boost leaks on 2 of those hoses off the intake manifold.. I just removed the 4 hoses, cut the nipples and sealed them off… Then removed the hose from the PCV and just left the PCV in the oil air box attached to the block (again, permanently putting the PCV in closed mode)… So now i am ka-t with a shut PCV valve and all my crankcase gas' are exiting the VC all the time..!!

So again, according to the FSM, fresh air enters the VC & bad contaminated gas' exit the PCV… Im assuming the fresh air is there to help keep the contamination down to a minimum while the PCV helps to remove the bad gas… OR the fresh air into the VC is to help aid in allowing the crankcase to have a good ventilation system..

I have read about 1 catch can setup, PCV to catch can to intake manifold. Works great while at idle and cruise, but under boost the PCV or check valve will close, then the crankcase has to find another exit which is the VC which is usually hooked up to the turbo inlet.. which guess what it will start to get… Nasty oil vapors… which will be passed into the piping and intercooler… etc u get the idea..

the next setup is putting in 2 oil catch cans…. One for the PCV and one for the VC (while under boost). The one for the PCV seems to work fine while at idle & cruise.. But once in boost, the PCV or check valve will close to effectively forcing that crankcase gas to find another exit, which is usually out the VC… which in tern pushes into that 2nd catch can and back to turbo inlet. The only downfall i see is that when off boost, the VC is supposed to acting as a intake for fresh air… What fresh air can it get if its connected to a catch can which is full of nasty oil vapors… ?? The inlet of that catch can is where all the nasty oil and crap GO TO… Once the VC reverts back to intake of fresh air.. its not going to get any fresh air..

Then there is the PCV & VC vented to atmosphere… Which is kinda how my setup is. This setup we vent the PCV and VC to a catch can with a breather filter… If you put the PCV to atmosphere, it will NOT open because there is NO vacuum to open it. So running a hose from it to a catch can is worthless IMO. So if the PCV is now permanently closed, there is ONLY one exit for the crankcase and that is the VC which you have sent to a catch can with a breather filter…
This setup there is NO fresh air going into the VC to do its "factory purpose".. But you do have an exit for the crankcase to breathe out, how much it can breathe depends on what size your VC vent hole is and the size of the hose and the size of your filter breather.. They say this method contaminates your oil faster which requires more / sooner oil changes….

The next setup i saw was Tee'ing the PCV & VC together to the inlet of the catch can and the outlet to the turbo intake so that the turbo will evacuate the crankcase gas during idle, cruise and boost which seems like the perfect solution. BUT people say the turbo does not pull enough vacuum to extract the crankcase gas… Well, that is true.. there is NO Vacuum before the turbo, if any there will be like 1 inch… Here is the kicker that i see, people are leaving the stock PCV in there which again requires VACUUM to open… If the turbo cannot produce vacuum, then the PCV will NOT open which means the crankcase gas will have to find another exit… Which again is the VC. So again, hooking up a hose from a permanently closed PCV to a catch can is worthless. But with the VC also hooked to the same side, there is a exit for the crankcase gas to exit & be pulling in by the turbo.. Bad part is again, NO fresh air into the VC… This setup will work fine for idle, cruise and boost but* the No fresh air into the VC is a problem per the FSM and original engine design…

And here is what i plan on doing and its the best solution that i can "think" of while retaining ~full PCV function during idle, cruise and boost so that i can preserve my oil so that i don't have to do as much oil changes and to preserve internal seals and gaskets and so that the crankcase does not get "accidentally" pressurized under boost which will cause other problems….

Remove the PCV and place a 3/8 NPT to 5/8 hose barb into the stock air oil separator on the block… Then a hose from it to a GOOD catch can, then to the turbo inlet. On the VC i will put in a 5/8 breather because the nipple on the VC is a 5/8 which allows a good amount of air flow :-)
With this setup the turbo will be doing all the work. As it spins during idle, cruise and boost, it will be sucking out the crankcase gas' while allowing the VC to allow fresh air IN….. All this is done via a 5/8 hole on top & bottom which SHOULD allow plenty of air flow for that crankcase to BREATHE… Remember no PCV that needs to be pulled open by vacuum that does not exist via turbo intake…
The ONLY downfalls i see here is the physical amount of air flow the catch can will allow to pass thru OR the amount of air the turbo can suck out of the crankcase or if the catch can will restrict the turbo's suction.. Remember as the turbo spins and sucks out the crankcase gas, the VC is allowing air IN. Its a constant cycle during idle, cruise and boost… and remember again that crankcase pressure and blow by is at its peak while the motor is under boost so thats when crankcase evac is the most important..

SO… what do you guys think on my setup.. Im pretty sure my idea will work pretty good, but i think its a lot better than i some of the setups i can seen on the web… I am NO MECHANIC is any way shape or form, i am NO expert in PCV setups, i am not saying i know everything, because if i did, you would not be reading this.. LOL I'm writing this post in hopes to get your feedback and let me know if i am wrong… I am OPEN to all comments and corrections..

thanks guys...

Before you remove the pcv and go about setting this up, you should consider your goal. There are really only 2 that I can think of, but it's early and I'm on half a cup of coffee.

1, Stop pressurizing the crankcase on boost and spitting/leaking oil because of it. With the VC open you're not pressurizing anything. So no worries there.

2, Removing the blow-by from the crankcase.

It sounds like you're worried about all that blow-by in your oil. Which is understandable. I would start by putting the hose before the turbo and measuring how much vacuum/airflow you're able to achieve. Everything really depends on this one aspect. You may need to use some sort of venturi fitting. I'd attach a vac gauge to the end of the hose and play around with different positions and see which one "pulled" the most. If you use a venturi you may be able to pull vacuum on the crankcase. I would seal the VC if you do pull vac. This will help seal the piston rings, prevent leaks AND pull all the carbon blow-by out.

This is going to require a really good oil air separator. Or else you're going to fill your entire intake tract with oil and sludge. Maybe two catch cans, each filled with some sort of media. Not just an empty catch can.

In order for this to work, you should do some testing.

WDRacing wrote:Before you remove the pcv and go about setting this up, you should consider your goal. There are really only 2 that I can think of, but it's early and I'm on half a cup of coffee.

1, Stop pressurizing the crankcase on boost and spitting/leaking oil because of it. With the VC open you're not pressurizing anything. So no worries there.

2, Removing the blow-by from the crankcase.

It sounds like you're worried about all that blow-by in your oil. Which is understandable. I would start by putting the hose before the turbo and measuring how much vacuum/airflow you're able to achieve. Everything really depends on this one aspect. You may need to use some sort of venturi fitting. I'd attach a vac gauge to the end of the hose and play around with different positions and see which one "pulled" the most. If you use a venturi you may be able to pull vacuum on the crankcase. I would seal the VC if you do pull vac. This will help seal the piston rings, prevent leaks AND pull all the carbon blow-by out.

This is going to require a really good oil air separator. Or else you're going to fill your entire intake tract with oil and sludge. Maybe two catch cans, each filled with some sort of media. Not just an empty catch can.

In order for this to work, you should do some testing.

ok, so what about the fresh air getting into the motor via VC breather..?? What is your take on that..?? Do you think its necessary..?? Why does the factory setup do this..??

Next question is, if one side is sealed shut and i pull from the other end, does it REALLY matter which end i pull the crankcase vapors from..?? If you look at the bigger picture, its all one big L shaped chamber. The only thing i can possibly see is that MOST of the nasty stuff will be on the bottom side of the motor and not the head/valve cover side.

Here's a useful link for anyone going the GM smog pump route - Racetronix Smog Pump Harness w/ Hobbs Switch

I plan on going that route, probably early next year, sooner if my Evo
would hurry up and sell

WD, didn't you say a PCV valve was just a check valve? I re-read the article in the OP and it says a PCV is a check valve but also limits flow to prevent A/F issues, and that's why the OEM PCV valves are the best replacement. If you didn't say that, my bad, just wanted clarification.

If that's the case I will use multiple OEM PCV valves(and possibly plain check valves) in my plan to have intake vacuum pull crankcase/VC fumes off boost, and the smog pump (into turbo inlet) while on boost, through two Saikou Michi DC3 catch cans, with a checkvalved bypass around the smog pump incase of smog pump failure, and a hobbs switch to a warning light to flash if I ever have the valves fail and pressure up the crankcase/VC (the intake manifold source). Thoughts? Hopefully that covers all the bases.

rn240sx wrote:

WDRacing wrote:Before you remove the pcv and go about setting this up, you should consider your goal. There are really only 2 that I can think of, but it's early and I'm on half a cup of coffee.

1, Stop pressurizing the crankcase on boost and spitting/leaking oil because of it. With the VC open you're not pressurizing anything. So no worries there.

2, Removing the blow-by from the crankcase.

It sounds like you're worried about all that blow-by in your oil. Which is understandable. I would start by putting the hose before the turbo and measuring how much vacuum/airflow you're able to achieve. Everything really depends on this one aspect. You may need to use some sort of venturi fitting. I'd attach a vac gauge to the end of the hose and play around with different positions and see which one "pulled" the most. If you use a venturi you may be able to pull vacuum on the crankcase. I would seal the VC if you do pull vac. This will help seal the piston rings, prevent leaks AND pull all the carbon blow-by out.

This is going to require a really good oil air separator. Or else you're going to fill your entire intake tract with oil and sludge. Maybe two catch cans, each filled with some sort of media. Not just an empty catch can.

In order for this to work, you should do some testing.

ok, so what about the fresh air getting into the motor via VC breather..?? What is your take on that..?? Do you think its necessary..?? Why does the factory setup do this..??

Next question is, if one side is sealed shut and i pull from the other end, does it REALLY matter which end i pull the crankcase vapors from..?? If you look at the bigger picture, its all one big L shaped chamber. The only thing i can possibly see is that MOST of the nasty stuff will be on the bottom side of the motor and not the head/valve cover side.

You might run a little more rich because there will be slightly less air going to the motor. I have PCV system disconnected and have for quite some time. Just running the VC vented to the atmosphere. She runs fine. Check your own readings out with a wideband before and after. That way you'll know exactly what's going on.

I'd pull vacuum from the VC for the reason you already stated.

GTR PrYdE wrote:WD, didn't you say a PCV valve was just a check valve? I re-read the article in the OP and it says a PCV is a check valve but also limits flow to prevent A/F issues, and that's why the OEM PCV valves are the best replacement. If you didn't say that, my bad, just wanted clarification.

If that's the case I will use multiple OEM PCV valves(and possibly plain check valves) in my plan to have intake vacuum pull crankcase/VC fumes off boost, and the smog pump (into turbo inlet) while on boost, through two Saikou Michi DC3 catch cans, with a checkvalved bypass around the smog pump incase of smog pump failure, and a hobbs switch to a warning light to flash if I ever have the valves fail and pressure up the crankcase/VC (the intake manifold source). Thoughts? Hopefully that covers all the bases.

The PCV limits flow so you're not continuing to suck an increasing amount of unmetered air into the system. By limiting flow it's easier to determine how much air is ingested and compensating the tune for it. The good thing about that is, you can disconnect it and your car will still function as normal.

Your system sounds good, but overly complicated...lol. I suppose a light of some sort is ok, but I'd just hook a vacuum gauge to the VC. That way you can tell what vacuum you're pulling at what rpm etc. Basically how well your system functions at whatever given point. Hope that makes sense.

The only thing I would use a check valve for is to insure you're not having boost pressure reach the block.

I like the idea of a vacuum gauge, or a vacuum/boost gauge for monitoring PCV performance, I just don't know about the gauge mounting, since I have a few that I still want to add. A small discrete led light would be beneficial if I don't have the room, but i'll definately keep that in mind. I plan on this being a set it and forget it setup (with dumping the catch cans as the only maintenance of course.)

At least use a gauge temporarily at the beginning. So you can truly asses the performance of the system. Then remove it or relocate it to the glove box or something.

So I just read through this entire thread, just happened to come across it browsing. I have just one question regarding this debate... Why not mock a pcv system after that of a factory turbo car with the same parts said system utilizes AND with the added use of a catch can b4 the intake mani?

And if the goal is to completely keep harmful gasses out of the engine then use an electric pump system. Seems like a simple answer to a complicated question.

Scuffed_ChukiCoupe wrote:So I just read through this entire thread, just happened to come across it browsing. I have just one question regarding this debate... Why not mock a pcv system after that of a factory turbo car with the same parts said system utilizes AND with the added use of a catch can b4 the intake mani?

And if the goal is to completely keep harmful gasses out of the engine then use an electric pump system. Seems like a simple answer to a complicated question.

That's pretty much the gist of it. The reason for the longish explanation and discussion is to explain the why and how of the PCV system.

An electric pump is really the best method.

Gotcha, but with the use of the pump u say run a can prior to the punp, well where does the gases go after the pump?

You can route it back to the intake pipe after the MAF.

what if you don't want the gases being recirculated. Can it just vta?

Scuffed_ChukiCoupe wrote:Gotcha, but with the use of the pump u say run a can prior to the punp, well where does the gases go after the pump?

VTA, another catch can or wherever you'd like. I don't have emissions or inspections where I live, so I'd just VTA.

Route it into the cabin for some happy times.

That takes the term vapor lock to a whole new level.

WDRacing wrote:That takes the term vapor lock to a whole new level.