Dinan s/c kit 3-way valve Q

[Jason C SBB]

This is the valve with 3 (large) ports that connect to the valve cover, the s/c inlet, and the cyclone separator.

Car is a 97 M3 with basic Dinan s/c kit.

Is this operation correct:
During vacuum, the valve cover connects to the cyclone separator.
During boost, the valve cover connects to the s/c intake.
OR is it:
During boost, the cyclone separator connects to the s/c intake?

My car has a problem in that oil drips from the intake filter. I'm trying to figure out if the 3 way valve was connected wrong by the P.O.

[Jason C SBB]

I called Dinan and they answered my question.

The answer is during boost, the valve cover connects to the s/c intake (and seals off the line from the cyclone separator). Sealing of the line from the CS prevents boost in the intake mani from escaping up this route.

This is so that off-boost, the connection is like stock; the cam cover connects to the CS. In boost, the cam cover goes to the Dinan provided catch can, and the blowby vapors go to the s/c inlet pipe.

In my car, the previous owner had the port for the cam cover and the CS switched! This explains my problem of the car seeming to leak oil and smelling when driven hard - this made blowby pressure build up in the crankcase under boost!

The way to ID which port is which:
The port opposite the small vacuum nipple goes to the s/c inlet.
The 2 remaining ports are 2 different sizes - the larger one goes to the cam cover.

You can verify this by blowing through the port for the cam cover - it should blow through to the port for the CS. The port for the s/c inlet should be sealed. Apply vacuum to the vacuum port. Blow through the port for the cam cover - it should blow through to the s/c inlet, and the port for the CS should sealed. Instead of applying vacuum, for the purposes of double checking which port is which, you can press up on the plunger with a narrow deep socket or other blunt object - press up on the port opposite the vacuum port.

To test it:
Place a few psi with a mityvac, up to 10 psi, on BOTH the vacuum port and the port from the CS. You need a lot of fittings. Pressure should leak at < 1 psi per 5 seconds (as per Dinan). If it leaks, place it under water to verify source of leak is not your fittings.


In addition to the 3way valve, there is a 2nd vacuum operated valve between the CS oil drain line and the dipstick. Off-boost this valve is open, and allows oil to drain. In boost the valve closes, to prevent a) boost in the intake mani to flow through the CS and into the dipstick tube, and it also prevents blowby pressure (if higher than mani pressure) from causing oil to back up to the CS and possibly into the intake mani.

Inside the CS itself, it has a valve acting on the port connected to the intake mani. It acts like a typical PCV valve - it is open under partial vacuum, and closes the port off at higher vacuum such as idle. The port coming from the cam cover is what goes thru the actual air/oil separator, and oil drips out the bottom port which goes to the dipstick.

[Adriano]

Awesome! I know this post is old but it helped me out of a jam. Thanks again