PCV System Mod

[FordNut]

Well, here's another approach to the PCV system, with an integrated crankcase vacuum pump.

Start to finish...
1. Air goes into the valve cover after going past the MAF sensor.
2. It goes through the crankcase and comes out the other valve cover.
Normally it would go through a PCV valve now and go to the intake manifold.
3. My setup is modified so the next thing is the Romak PCV trap.
On the outlet of that I have a T and the Cobra PCV valve which connects back to...
4. The fitting for the intake manifold vacuum.
5. The T fitting then connects to a check valve before going to the vacuum pump.

[FordNut]

6. The other side of the check valve will connect to the inlet of this pump.
It is normally used as an emission system pump on a Mustang.
7. This is the bracket I made for the pump.
It started life as a standard bracket for installing the pump on a Mustang.
8. This is where the outlet of the pump will connect to.
This point is after the MAF, before the TB, so it won't see vacuum or boost and all the air that goes past the MAF stays internal to the intake side of the engine.
You don't see, inside the TB elbow is a fitting attached to the external fitting, it is the plastic elbow fitting that is normally attached to our OEM PCV valve and it is pointed at the TB so that when the pump is on there is no turbulence sensed by the MAF.
9. Test-fitting the pump & bracket on a spare fenderwell liner.
10. Pump installed.

[FordNut]

11. This is the switch that comes with a BAP, it will switch on the pump when the engine is under boost.
The pump is not rated for continuous duty and it's not really useful unless the car is under boost.
12. This is the check valve I selected, it is normally used for a Corvette pollution pump.


Theory of operation...
Engine idle, part throttle, no boost: Fresh air flows in the valve cover, through the crankcase, out the other valve cover with vapors possibly picked up, through the trap where the vapors are filtered to reduce oil, through the PCV valve, to the vacuum side of the intake manifold. For the Cobra this vacuum is normally obtained from 2 places, a hose and fittings connects from the bottom of the manifold, to a T where the PCV valve connects, then to the inlet of the blower at the plenum. Both of the connections should be at the same vacuum level since the bypass valve is open (with the Whipple it's a HUGE bypass valve). The check valve connected to the outlet of the trap will be closed at this time because vacuum from the intake manifold is pulling it closed as well as pulling the PCV valve open.

Moderate throttle, no boost: Fresh air can flow in the valve cover but there is really nothing to draw it in and if there is a lot of blowby air could actually flow out of the valve cover and back into the throttle body. Air and vapors can flow out the other valve cover and through the trap to the intake manifold, or even through the check valve and the pump even though the pump is not running. It is a centrifugal type pump so the air could flow through it if there is a whole lot of blowby. The bypass valve is probably still open, but the vacuum gauge is setting at '0' so it has neither vacuum nor boost. It is possible that air is flowing through the vacuum tube from the bottom of the manifold to the top of the manifold and creating a small amount of vacuum at the T fitting too, so if there is a lot of blowby it has 2 possible paths to follow.

Heavy throttle, in boost: Fresh air flows in the valve cover, through the crankcase, out the other valve cover with blowby vapors picked up, through the trap where the vapors are filtered to reduce oil, through the check valve, to the inlet of the pump, out of the pump and back to the inlet of the throttle body. The pump is turned on by the BAP Hobbs switch so it is pulling air through the check valve as well as keeping the PCV valve closed. For the Cobra's normal intake manifold vacuum connection, air will be flowing through the tube between the top and bottom of the manifold which could possibly put pressure on the Cobra PCV valve and close it or it could possibly create enough vacuum from airflow across the T that blowby could follow that path through the PCV valve.

[MM_BKK]

Hey FordNut,

Can you draw a diagram on paper and scan it as image?
Sorry, I think I'm retarded but I'm having a hard time following your description. I think a diagram could explain it better. Thanks.

[FordNut]

Hey FordNut,

Can you draw a diagram on paper and scan it as image?
Sorry, I think I'm retarded but I'm having a hard time following your description. I think a diagram could explain it better. Thanks.

I'll do a diagram and post it in a bit. It may be tomorrow before I get it done...

[bob6364]

I could use one also...Thats some deep thinking right there

[MM_BKK]

I'll do a diagram and post it in a bit. It may be tomorrow before I get it done...

Ok, that's cool. Thanks.

[Local Boy]

That's really AWESOME! Brian...

Glad your one of us!!!

Aloha

[FordNut]

Here's a pdf...

[4play]

what do you gain by doing this?

[FordNut]

First, the PCV system stays intact. If you delete the PCV system you have to put breathers on the car and they will eventually cause an oily mess. The PCV system is important because it evacuates gases from the crankcase which can cause oil and internal engine parts to deteriorate. When properly connected it also keeps all of the airflow paths in a metered part of the intake system (everything goes through the MAF).

Second, the addition of the trap reduces the amount of oil in the vapors which are in the crankcase from going through the PCV valve and back into the intake manifold. The oil getting back into the intake creates a big mess inside the manifold (some of them I have removed have a puddle in the bottom) and theoretically it reduces engine power because the oil vapors mixed with air/fuel don't burn as well as plain old air/fuel.

Third, using the Cobra PCV valve provides a more positive seal to prevent boost from getting into the crankcase. The OEM PCV valve allows flow both directions. When you blow on it in the reverse flow direction, air still flows through it. It flows less air than it does in the forward flow direction, but it does allow flow. Boost getting back into the crankcase can cause seals and gaskets to leak as well as reducing power.

Fourth, adding in the check valve and connection to the intake system (even if the pump was bypassed) allows a flow path for the crankcase pressure if there is blowby under boost. The PCV valve should be closed under boost, and the cylinder pressures are at their highest under boost. The probability of having blowby at this time is at its highest, but there is no flow path for it to get out of the crankcase since the PCV valve is closed. This can cause leaks and reduce power, plus it leaves the blowby gases in the crankcase where they can contribute to oil deterioration.

And Finally, the pump creates a positive flow for the crankcase evacuation. It isn't powerful enough to generate much vacuum in the crankcase but it can generate a little bit of vacuum. Some racers put various types of crankcase vacuum pumps on their cars, it supposedly increases power output. Supposedly power is increased because of a couple of things, the pressure differential between the combustion chamber and crankcase is higher which helps ring sealing and the vacuum in the crankcase provides less resistance to piston motion in the crankcase. Some of the vacuum pumps used by racers are belt driven and they create a lot more vacuum but they don't last too long for street use. The pump I used is not rated for continuous duty so I have the switch to turn it on only under boost. Based on reports from others who have used this pump it doesn't like oil in it, so the oil trap should help in that regard.

Some of the info on this mod came from Stillen, some from the GN guys, as well as several other sources.

[MM_BKK]

Nice set up! Now I understand your plumbing.

I guess that's why most race engines run dry-sump lubrication system, aside from their extra oil capacity, they really benefit from the crankcase vacuum all the time created by their belt driven scavenger pump system. The only 2 American made cars that I know of that have factory dry-sump set up are the new Corvette ZR-1 and the Ford GT40 Supercar.

I may have to look into a dry-sump set up on my next build...

[4play]

cant you just use a vaccume container to colect the junk but still have the gasses through?