- Tue Mar 25, 2008 9:12 pm
#47697
Under high RPMs, the crankcase pressure exceeds the limit that the PCV system can flow. So there is a baffled breather tube on the valve cover connected directly to the intake tube. In high RPMs, or when your PCV system is unfortunately clogged, excess crankcase pressure is pushed out into your intake tube. They use the intake tube to keep it a closed system, so you're not polluting the air, dripping oil on the ground, and you don't get that funky egg smell in the passenger cabin. Even still, this is not enough breathing for a Honda VTEC motor. So oil gets pushed past the seals and power is slightly diminished. You have the problem of blowing your spark plug wires out of the tubes. People modify the valve cover to increase the breathing capacity of the even further to prevent this problem.
The result of this unfiltered connection to the intake tube is the same as with the intake manifold connection to the PCV: effectively decreased octane, a dirty throttle body, a dirty IACV, and a dirty intake manifold.
On a turbo or supercharged vehicle, you can see there's a problem because under boost, the pressure inside the intake tube and intake manifold is going to be much higher than in the crankcase. In fact, it's going to push into the crankcase and increase the pressure. Below boost a FI car is the same as a N/A car.
So now the problem becomes "how do I re-plumb a stock N/A system when I turbo charge the car". The only way for me to explain this properly is with a diagram; unfortunately I don't have my scanner with me.
Basically you get a couple of brake booster line check valves from the junkyard. These will act as PCV valves (but much more reliably) and only allow air to flow in one direction. That way you can still take advantage of the vacuum present in the intake manifold when you're not under boost.
The pre-turbo intake tube is capable of creating vacuum (when the engine is under boost) if you weld in a slash cut tube. This line can be T'd in to the intake manifold line so that you will always have vacuum removing pressure from your crankcase.
Another option is to use a slash cut in the exhaust, but because of heat issues, this is more difficult.
You absolutely do not want any oil vapor going into the turbo, so you will use a baffled catch can that has an oil-air separator. Both the turbo line and intake manifold line can be T'd off the clean side of the catch can. This eliminates the PCV valve and increases the breathing capacity of the crankcase ventilation system.
The valve cover line should be connected to the dirty side of the catch can.
The engine block side of the PCV line is connected to the bottom of the catch can so that oil can drip back into the crankcase. People who have seen the afterbirth come out of a catchcan are understandably reluctant to have this go back into the oil pan. But there really is no problem as long as you replace your oil and oil filter regularly. It is so much better than frequently draining a catch can on a street car.
Last edited by suspendedHatch on Wed Mar 26, 2008 6:56 pm, edited 1 time in total.
