It's just for venting crankcase pressure, so you CAN plug it and run a vented oil fill cap, but I would keep it. It's a perfectly good working, dependable design that does exactly what it's supposed to. You could say the exact same about vented oil caps, and even more dependable, but they tend to leave an oily residue running down your engine and fogging oil onto anything near by. The PCV system takes that oily pressure and routes it back into the engines cylinders to be burnt up and go out the tail pipe.
You can run a hose from the cap to a catch can to prevent an oily mess. I recently put a working PCV back in because I was getting a lot of condensation building up under my valve covers. It dried things right up. Now I have a small boost leak into my crank case.
The point of the PCV is to vent the blow-by gases from the crank case. Of course the emissions people don't want those gases vented into the air anymore (old draft tube style) so it's put back into the intake air stream. The blow-by gases contain a little moisture that can build up inside your engine (as Justinbart noticed) so it's highly suggested not to block it off.
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12:53 PM
1fatcat Member
Posts: 1519 From: Zimmerman, Mn Registered: Dec 2010
I gotta ask, if your running a PCV system, how do you know your getting boost into the case? Not making fun, because thats something you don't want. I'm just wondering if you have a pressure guage in the crankcase?
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01:53 PM
Darth Fiero Member
Posts: 5922 From: Waterloo, Indiana Registered: Oct 2002
You can run a hose from the cap to a catch can to prevent an oily mess. I recently put a working PCV back in because I was getting a lot of condensation building up under my valve covers. It dried things right up. Now I have a small boost leak into my crank case.
Does anyone know of any total seal PCV vales?
It is a crap shoot when it comes to PCV valves. I've bought some new ones that seal almost perfectly when you try to put pressure thru them (as boost would do) and the very next one I've bought from the same store doesn't seal as well.
You don't need a PCV valve that seals "perfectly". One that blocks 99% of the boost flow will work fine (these are the ones that if you try to blow thru them with your mouth, very very very little air is permitted to blow thru). You may just need to check out all the PCV valves your parts store has on the shelf (for your particular application) until you find one that seals good. But like I said, it doesn't need to be completely perfect. Your piston rings are going to allow far more blow-by during boost than your PCV valve will. As long as you are still running a breather, you'll be ok.
-ryan
------------------ OVERKILL IS UNDERRATED Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com
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02:59 PM
darkhorizon Member
Posts: 12279 From: Flint Michigan Registered: Jan 2006
The question is, how much pressure do you make with your lungs? The answer is.... very very very little.
when you ramp things up to 20-25psi, things become significant.
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You need to keep in mind the way the PCV valve is designed, the more pressure that is put on it in reverse (to simulate boost pressure), the more it will try to shut off the flow (by pushing that metal disc inside of it against the opening in the bottom of it). If you want, buy a bunch of PCV valves, take them home, and try blowing some regulated shop air thru them and see how well they seal. The pick the best sealing one for your application and call it a day.
I think you guys are missing the point on this though... Your piston rings are going to let FAR MORE boost pressure past them (blow-by) than the PCV valve ever will. Yes, I agree you don't want a gross PCV boost leak. But even using a PCV valve that doesn't seal against boost all that great probably won't cause any problems for you - as long as you are using an open element breather. You certainly don't want to allow any pressure to build in the crankcase. And you DO want to run a PCV valve because it will help evacuate the moisture from the oil and crankcase. The last thing you want is excessive water contamination of your oil.
quote
Originally posted by darkhorizon:
In terms of a stock SC motor... No breather is the only way to do things. A breather creates a "post maf air leak" letting unmetered air in the motor
If you are running a PCV valve, you MUST use a breather. The bone stock 3800 Series 2 SC engines have both a PCV valve and an internal breather passage that leads back to the stock throttle body. Series 3 engines have an external breather hookup. In either case, in a bone stock factory application, the breather has access to a filtered outside air source between the throttle blade and MAF sensor. This means the air going into the breather system is being measured by the MAF sensor.
Capping this off and running an open element breather (in the oil cap or elsewhere) will mean the air the breather system draws in to replace the vapors the PCV system consumes will NOT be measured by the MAF sensor. But, it is such a small amount, it doesn't really impact things that much. This can easily be tuned around; people have been doing it for years (even back in the days of the MAF TPI V8 engines), and nobody has had any significant problems by running it this way.
People who add turbos to 3800 Series 2 and 3 engines need to make sure the breather system can't get boost pressure put to it - so that usually means we have to use an open-element breather filter. That's the way it is set up on my own Fiero and that's the way it has been set up on countless other 3800 turbo (and even SC) applications. I've never had a problem with my MAF tuning being thrown off by this (my fuel trims are perfect) so I just don't see why you keep bringing it up, DH. It is a non-issue.
-ryan
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10:46 PM
May 13th, 2011
americasfuture2k Member
Posts: 7131 From: Edmond, Oklahoma Registered: Jan 2006
so putting a breather in the oilcap is just for those that removed the PCV? afaik the PCV is still in my supercharger. i havent changed anything with the PCV.
There are 3 types of crankcase ventilation. Originally there was the Draft Tube which let air out of the crankcase and the air that replaced it came in through a vented filler cap. Then for emissions the draft tube was replaced by the Open PCV system which still used the vented filler cap but the draft tube was replaced with the PCV valve and a tube that fed into the intake. Nowadays they use the Closed PCV system which replaces the vented filler cap with another tube that leads to before the throttle body to suck filtered air into the crank case (to allow the bad air to vent).
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10:50 AM
Darth Fiero Member
Posts: 5922 From: Waterloo, Indiana Registered: Oct 2002
so putting a breather in the oilcap is just for those that removed the PCV? afaik the PCV is still in my supercharger. i havent changed anything with the PCV.
Not exactly. No matter what you must run some kind of breather setup. You cannot seal off the crankcase - otherwise pressure could build in it and blow out gaskets (or vacuum could build in it and suck in the gaskets - if you are using a PCV valve).
ALL factory engines ran some kind of breather. Some ran the breather passage integral to the throttle body (like the Series 2 engines) and others ran it externally (like the 3800 Series 3 engines and other GM 60 deg V6 engines).
If you have an engine that has the integral breather passage and you are going to run a turbo, then you need to block that passage otherwise boost pressure could get to it. And in this case you would need to run an oil cap breather.
If you have a Series 2 engine where you've installed an aftermarket throttle body and adapter plate that blocks off the integral breather passage, then you'll need to run the oil cap breather.
If you have a Series 3 engine, the breather passage runs to an external port on the top of the intake/blower that the factory application connected a hose to which ran to the induction tubing. So you could just put an open-element breather filter right on this port. Here's a picture showing the crankcase breather port on a Series 3 blower housing (port is on the very right side of the picture - it is the metal hose nipple sticking up out of the blower housing):
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12:30 PM
PFF
System Bot
americasfuture2k Member
Posts: 7131 From: Edmond, Oklahoma Registered: Jan 2006
Should be fine hooking it up that way AS LONG AS that port on the top of the throttle body is for a breather tube and it isn't a vacuum port. I'm pretty sure that port on the throttle body he's got the breather tube hooked up to is for the breather and it doesn't lead to vacuum. The way to tell is to find out what side of the throttle blade the passage that tube runs into goes to. If it leads to a passage between the throttle blade and the supercharger housing, then it is a vacuum port. If it leads to a passage that faces outward from the engine (on the side of the throttle blade that you would hook your induction tubing to), then it is for a breather.
I gotta ask, if your running a PCV system, how do you know your getting boost into the case? Not making fun, because thats something you don't want. I'm just wondering if you have a pressure guage in the crankcase?
the line MUST be before the Turbo/supercharger. NOT after. same for EGR if it is kept. when the engine is running you will feel Vaccuum (or measure vac) at the correct point. the wrong spot will have pressure when revved up or under load (as in a turbo) I have seen guys that added a turbo and did not reroute PCV and blew seals/gaskets.
If running boost at all I strongly suggest adding a catch can, it will keep the intake a whole lot cleaner.
[This message has been edited by timgray (edited 05-13-2011).]
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06:50 PM
americasfuture2k Member
Posts: 7131 From: Edmond, Oklahoma Registered: Jan 2006
Should be fine hooking it up that way AS LONG AS that port on the top of the throttle body is for a breather tube and it isn't a vacuum port. I'm pretty sure that port on the throttle body he's got the breather tube hooked up to is for the breather and it doesn't lead to vacuum. The way to tell is to find out what side of the throttle blade the passage that tube runs into goes to. If it leads to a passage between the throttle blade and the supercharger housing, then it is a vacuum port. If it leads to a passage that faces outward from the engine (on the side of the throttle blade that you would hook your induction tubing to), then it is for a breather.
here are some pics of my tb. his is also the same one i have, the N* tb. the port leads to after the blade, but that passage has an opening that goes to before the blade. im assuming this is the correct spot to hook up the PCV hose.
back side of tb front side of tb passage for that port on the adapter plate.
[This message has been edited by americasfuture2k (edited 05-13-2011).]
I gotta ask, if your running a PCV system, how do you know your getting boost into the case? Not making fun, because thats something you don't want. I'm just wondering if you have a pressure guage in the crankcase?
Blowing on the top of the PCV, I can get air through there. So this means that there is a boost leak. This will hurt the turbochargers efficiency. How much? I don't know. I've always read that you don't want any boost leaks. I soap up all my couplers/joints and pressurize my system to fix any leaks.
I guess I'm more concerned with my turbo working harder with air that is lost than extra air getting in my crank case.
here are some pics of my tb. his is also the same one i have, the N* tb. the port leads to after the blade, but that passage has an opening that goes to before the blade. im assuming this is the correct spot to hook up the PCV hose.
back side of tb front side of tb passage for that port on the adapter plate.
Looks fine to me. You should be ok using this port as the breather hookup. The adapter plate blocks off the back portion where this tube dumps into and only allows fresh air to enter from IN FRONT of the throttle blade. This setup will be fine for a supercharged application.
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03:50 PM
Darth Fiero Member
Posts: 5922 From: Waterloo, Indiana Registered: Oct 2002
