stupid question

does anyone know what the point of the vaccum line on the side of the valve cover going to the intake pipe is for,what it does,do u need it. im building a motor and if i dont need it im going to weld it closed. thanks it a 1g.

you mean where the PCV valve is? It's recommended you have it. It keeps pressure balanced in there. Without it pressure might build and you will probably blow gaskets. If it's what I think your talking about that is, I can recommend possibly putting an inline filter in though since oil does tend to travel through it sometimes.

No, I dont think he is talking about the PCV valve. The line your talking about isin't a vaccum line, its just a breather, but im not sure if you can close it up.

You are going to need it.

it is the PCV and it is not a good idea to plug it up or let it vent to the atmosphere.

It is NOT the PCV, he's talking about the breather like Silver said, and you can not close that off. The reason that you have that is so the pressure in the valve cover can escape via the breather into the intake (which is never good because sometimes oil finds its way through the line and it runs into your throttle body and it can run through the small holes in the bottom of the throttle body and clog the IAC motor). So what I would do is just put one of those small breather filters you can get from like Autozone and put that on it.

The PCV valve is on the back side of the valve cover and that takes pressure from the block and releases it into the valve cover so it can escape.

thanks for info

The more boost you run more likely the more oil to come out that hose. What alot of us do is make or by a oil catch can. Alot of people do not like the idea of that oil going into the turbo through the IC piping. What alot of poeple also do cheap is get a inline gas filter, a see through kind and just cut the hose and connect it ;) They are like $3.20, thats what i was doing for the longest time.

Just want to clear a few things up.

The PCV valve is for Positive Crankcase Ventilation. When the intake manifold is under vacuum, it opens and a vacuum is pulled on the crankcase (block, oil pan, head/valvecover, etc). Any combustion fumes that pass the rings or oil vapors will be pulled into the intake and burned before being released to the atmosphere. The whole point of this is reduced emissions. Under boost, a check valve closes to prevent pressurizing the crankcase, which is bad, see next section.

The valve cover vent going to the intake pipe is to let excess pressure under boost from blowby be released. It's released into the intake to ensure it is burned completely before entering the atmosphere, again, for emissions. Positive pressure in the crankcase is always bad. It increases the density of the air in the block increasing pumping losses (don't forget the bottom sides of the pistons also have to move air around ;)). It also makes it much more difficult for the piston rings to make a good seal, compounding the problem. High HP race motors can get some good blowby at high boost. This is what pops the dipstick out on some cars. I run 2 valve cover vents, others have run more. Some race cars run electric or belt driven vacuum pumps to pull a stronger vacuum on the crankcase. A bad PCV valve can also allow manifold boost to enter the crankcase, raising pressure, and essentially creating a boost leak since the VC vent goes to the intake pre-turbo. High HP cars should remove this valve to be safe, or at least replace it often. A brake boost fitting from an intake manifold will thread right into the PVC port (1/8th BSP threads) allowing for another 3/8th vent line to be attached. This is not legal for emissions though. Another thing to note is that venting the valve cover to atmosphere will bollix your fuel trims. DSMlinkers, forget about using global and dead time to adjust trims in this configuration, unless you don't mind compensating for WOT with the sliders. This is the reason the factory runs this line to the intake post MAS.

Hope this helps.

Kevin I still think you should write a book. You are one of the most knowledgable DSM'ers that I know of.

I would, but DSMers are too broke or too cheap to make it worth my time :D Someday I'll start adding this stuff to my website, which is the next best thing, even though it actually costs me money :) And thanks for the kind words, as usual.

:1:

Kevin, I am forever your slave. *worships Kevin* lol

just to throw my two cents in here you can buy a really cheap fuel filter at autozone, (I think it's the 3/8 inlet/outlet) and use that as a catch can. Just cut that rubber line and line up the arrows on the fuel filter, make sure it goes the right way. It's like 1.50 and works just as well as any catch can. I replace it every oil change.

I made one out of a 4" section of 2" PVC, two end caps, two of those inlet things (like on a MBC), and a ghetto plastic valve (to let the oil out). I thought it was pretty sweet, it was only like $8.