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V8 > 3G
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Discussion Starter · #1 ·
I've been pondering the idea to throw a catch can on the pcv system for a while and I'm not totally sure if I need a can or not. My current setup runs like this...

From the front valve cover there's a pcv check valve (evo pcv) and that runs to the lower intake mani. From the rear valve cover there's a pcv just venting to atmosphere. The rear pcv often drips oil and shit.

Now the way I have it setup allows the crank case to vent all the time with no unmetered air entering the system. Also, with this setup it doesn't see a vacuum source when boost kicks in so it's really only venting positive pressure under load.

If I was to route a catch can to the rear pcv valve and then route another line of the can to piping between the turbo inlet and filter would that in turn put the crank case under constant vacuum under boost?
 

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Stage 1 SDS @11+ psi
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Why don't you have the rear pcv hose going inbetween your MAF and the turbo inlet? What does the rear valve cover pcv hose go to now? A filter? Another pcv valve? That wasn't totally clear.

If you don't have a blow-thru-the-MAF setup, then there should be no reason why you can't setup your PCV system as stock. Why you have oil dripping from the rear could be two reasons: either you are pressurizing the crankcase and that is where the oil decides to leave, or oil is just splashing up there. I believe the former. The rear valve cover pcv hose opening is supposed to be the inlet (and only an air inlet) of metered air for the PCV system.

Once you get that straight, then you can determine whether or not you really need a catch can. I've gone back and forth on whether or not to install one. I've never found a whole lot of oil in the pcv valve hose, loss of oil in the crankcase, or any significant amount in the lower intake.

You need to think of when manifold vacuum is the highest. That might be when you get to the end of the race and let your foot off the gas to let the car gear itself down. Downshifting produces high manifold vacuum. Driving around when you are at -15 to -5 in/hg is a fairly low vacuum level that may not be strong enough to pull in oil, but just the bad crank case gases. During WOT or boost, there is no vacuum.

Some cars and some driving conditions may warrant the installation of an oil catch can. My friend LS1 needs it. Primarily because he has a high displacement engine that produced more vacuum that our cars, and his pcv valve cover design sucks. Again I'm not totally sure we need it I have one and may one day see if I actually accumulate any oil.
 

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V8 > 3G
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Discussion Starter · #3 ·
I don't have a MAF on this setup. On the rear bank there is simply a hose coming off of the valve cover with an evo pcv on the end.

My whole intention here is to put the crank case under constant vacuum and keep the contaminants from re-entering the motor. Alright since my rear PCV is simply hanging there I would route a hose from the PCV to a nipple on a catch can. From another nipple on the can I would run another hose to a portion of piping between the turbo inlet and air filter. In theory it seems like it's an ideal setup because under boost the vacuum level before the turbo will be increased as the turbo starts spooling and in turn, the vacuum level under boost on the crank case would increase.

Thoughts?
 

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Vortech Inside
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I'm pretty sure thats a good way to utilize a catch can, the rear valve cover pcv opening is an air OUTLET isnt it? I have a check valve there as well as in between the front valve cover and the intake manifold in order to insure nothing gets back in. Oil dripping out of there is common on certain setups and using a catch can in between the rear valve cover pcv and your turbo inlet shouldnt let any oil recirculate.
 

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V8 > 3G
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Discussion Starter · #5 ·
I'm pretty sure thats a good way to utilize a catch can, the rear valve cover pcv opening is an air OUTLET isnt it? I have a check valve there as well as in between the front valve cover and the intake manifold in order to insure nothing gets back in. Oil dripping out of there is common on certain setups and using a catch can in between the rear valve cover pcv and your turbo inlet shouldnt let any oil recirculate.
Correct. The rear is just venting to the atmosphere. I believe we have the same setup. I'm not sure what you're using to tune but if you're still using the MAS then you should probably have that rear PCV tied into your intake piping after the MAS.

My whole point of creating this thread was to gain info on whether or not there's any benefits to placing the crank case under vacuum during boost. I mean every car on the road utilizes vacuum in their stock form but once boost is added most people never seem to think about it. Could extra power be gained or even possibly a better running engine overall?
 

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Stage 1 SDS @11+ psi
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I'm pretty sure thats a good way to utilize a catch can, the rear valve cover pcv opening is an air OUTLET isnt it?
No, in the stock setup the rear valve cover pcv is an air INLET.

I don't have a MAF on this setup. On the rear bank there is simply a hose coming off of the valve cover with an evo pcv on the end.

My whole intention here is to put the crank case under constant vacuum and keep the contaminants from re-entering the motor. Alright since my rear PCV is simply hanging there I would route a hose from the PCV to a nipple on a catch can. From another nipple on the can I would run another hose to a portion of piping between the turbo inlet and air filter. In theory it seems like it's an ideal setup because under boost the vacuum level before the turbo will be increased as the turbo starts spooling and in turn, the vacuum level under boost on the crank case would increase.

Thoughts?
Guys, I think you have over complicated your pcv systems and now they don't work properly. Our engines are designed to bring in fresh clean air after the MAF & filter, mix that air with any gaseous contaminants, and then suck that mixture into combustion chamber to be burnt. I know you guys know that, but some how you've decided to deviate away from that design. Why? Because you have aftermarket FI systems? That is not a good reason, unless you have a blow-thru setup. The check valve you put on the rear inlet is creating more issues than it solves. I'd work the pcv system back to where it works properly and then you can think about the oil catch can.

I'll finish by saying what I said on another similar thread... If having the crankcase under vacuum is such a good idea then why don't cars come out of the factory like that?
 

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Stage 1 SDS @11+ psi
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Correct. The rear is just venting to the atmosphere. I believe we have the same setup. I'm not sure what you're using to tune but if you're still using the MAS then you should probably have that rear PCV tied into your intake piping after the MAS.

My whole point of creating this thread was to gain info on whether or not there's any benefits to placing the crank case under vacuum during boost. I mean every car on the road utilizes vacuum in their stock form but once boost is added most people never seem to think about it. Could extra power be gained or even possibly a better running engine overall?
That question has been discussed. Every car coming out of the factory has a working pcv system. Do you want to risk compromising your oil's integrity because the blow-by gases don't get removed properly?
 

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V8 > 3G
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Discussion Starter · #10 ·
That question has been discussed. Every car coming out of the factory has a working pcv system. Do you want to risk compromising your oil's integrity because the blow-by gases don't get removed properly?
Are you fully understanding my setup and are you aware that I'm running a standalone ecu with no MAS?

From the front valve cover there's a one way check valve that allows air to move from the valve cover into the intake mani thus relieving pressure and creating vacuum while out of boost. It functions as it came from the factory. However, during boost the pressure in the intake mani keeps the valve from opening. So during boost, when most blow-by occurs, the front pcv system does nothing.

Now on the rear bank I can't plumb the PVC back into the post-turbo intake piping because it will be useless under boost like the front bank. Without a vent, oil will be forced past the rings and your car will smoke like hell. So in order to keep unmetered air out and to maintain an unpressurized exit point I have a check valve venting to the atmosphere.

So to answer your question, no, my current setup relieves the crank case of all positive pressure under boost and functions as stock during normal driving.

With my idea to plumb a catch can between the rear bank and the turbo inlet I would no longer have a use for the pcv on the rear bank. Why? Because with a constant vacuum being created no unmetered air would enter. Under boost any blow-by gasses would be "drawn" from the crank case into the catch can where the gunk settles.
 

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Vortech Inside
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From what I understand, the check valves create a partial vacuum due to air only being allowed to exit the crank shaft. in its stock form, the inlet on the rear valve cover is supposed to provide air to be sucked in and mix with the blow-by gasses and out into the manifold by the intake manifolds natural vacuum. On an FI setup, this cant happen due to the boosted pressure so it escapes through the rear pcv. I don't see it creating any issues other than some oil and dirty air which is what an oil catch can is for.

As for the power and performance under vacuum, in theory yes a full on vacuum will net you the most performance because no extra power from the engine needs to be used to compress the air in the crankcase when the pistons go down. I think people have dynoed gains before on other platforms but I dunno about here.

This is what I read when I was looking at our pcv setup but i dont have any evidence to support it. Although it sounds logical and I have yet to have any issues.
 

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V8 > 3G
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Discussion Starter · #13 ·
take some pics if you can
Hope this helps.

Front bank (evo pcv):



Rear bank (evo pcv):



Where I want to plumb a catch can to before the turbo inlet (yes, the pipe isn't in place but just imagen that between the turbo and filter) :

 

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V8 > 3G
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Discussion Starter · #15 ·
Do it and dyno it, see if it makes a difference in power.
I have no doubt that my idea will yield power gains. My car is currently down right now because of a short in the wiring harness but by the end of march I shall have results.
 

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Stage 1 SDS @11+ psi
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I don't think this message board could handle every car built since 76. Do yourself a favor. Go start a car, pull the dipstick, and place your finger over the hole. I think you'll find the outcome very shocking.
OK I did your experiment, but I had to do it two ways. With my setup, there is no vacuum at the dipstick opening. I knew your setup has a check valve at the pcv inlet, so I blocked mine off and then checked the the vacuum at the dip stick. The vacuum was strong, which is incorrect.

And your assertion that every car before 1976 didn't have a pcv system would be correct, but I don't recall those cars applying manifold vac. to the crankcase. They were free to breathe out into the atmosphere.

I want to try to get away from this argumentative tone. It looks like we have different perspectives on the usage of the pcv system. (The only way to really tell is to do an oil analysis.) You started this thread by asking the effectiveness of a catch can. Almost all oil catch cans sold on the market today are for a working pcv system. To get the benefit, you need to get your setup to operate like stock. That was my point.
 

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Stage 1 SDS @11+ psi
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How about this. I know you are probably getting sick of me so I'll offer a solution using your pictures. Then I'll shut up. OK?

First remove the check valve from the rear bank cover. You won't need it any more. Then run a hose from that rear bank inlet to a nipple that you welded on that filter piping right where your finger is. Heck, you can even poke a hole on the top of the filter itself and jam the hose in there if you choose not to use your filter pipe extender. I've seen people do it. After doing that, your pcv system is working as it should.



Now all you need to do is put the oil catch can between the evo pcv valve and the nipple going into the mani. Obviously, you'll have to add hose to reach where you mount the can. So to summarize: filter pipe nipple (before turbo inlet) ==> rear valve cover inlet ==enginecrankcase==> pcv valve ==> can ==> mani. Done.:wavey:

 

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V8 > 3G
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Discussion Starter · #19 ·
Phil that's basically the plan I had. I want to get rid of the rear pvc once I run a vacuum line to pre-turbo. You say it will run as stock but wouldn't plumbing a line into the intake create a vacuum? That's what I'm going for but I thought you mentioned earlier that the crankcase sees no vacuum in the stock form. You've confused me. lol

Anyhow, I want to mount the catch can between the rear bank and intake piping because I don't want any debris going through the turbo. I'm not too concerned with placing a can on the front bank because under boost, when the most blow-by occurs, the front pvc is closed and nothing enters the intake mani anyway.

Fallowing me?
 

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Stage 1 SDS @11+ psi
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Phil that's basically the plan I had. I want to get rid of the rear pvc once I run a vacuum line to pre-turbo. You say it will run as stock but wouldn't plumbing a line into the intake create a vacuum? That's what I'm going for but I thought you mentioned earlier that the crankcase sees no vacuum in the stock form. You've confused me. lol

Anyhow, I want to mount the catch can between the rear bank and intake piping because I don't want any debris going through the turbo. I'm not too concerned with placing a can on the front bank because under boost, when the most blow-by occurs, the front pvc is closed and nothing enters the intake mani anyway.

Fallowing me?
I'll use colors to answer the corresponding questions. :)


The perception is that the inlet of the turbo is a vacuum 'black hole'. However, by tapping your pcv inlet a few inches away from the the turbo inlet, manifold vac. will always be more than the vacuum created by the turbo. You won't suck any crank oil into your turbo as long as the rest of the pcv valve system is working properly.

A working pcv system won't create any or nominal vacuum at the dip stick, because the vacuum is at the inlet. You see vacuum there because there is no other place for the air to get in. The whole purpose is to get air in to circulate the bad stuff out and burn it the combustion chamber.

OK I do follow you. I'll leave it open that the blow-by gases could build up enough to burp something out of the inlet. With our custom FI systems the blow-by can be higher than expected so maybe some thing needs to be on the front end. Maybe a simple canister filter would be sufficient? I haven't had such issues with my setup. The catch can was developed to combat the high vacuum that can draw in more than the blow-by gases. Try it on the front end if you like. I believe once you get everything setup, then you shouldn't have any issues.
 
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