Type R Club of America

Question about the OEM b series breather box and the ports it has. I don't have a blackbox on me right now, but this has been bugging me for a while on the function of two of the three ports.

I know one of the top ports connects the PCV to the intake manifold. But I am confused on the function of the two other ports. The other small port on top, is that where the oil returns back to the block? And is the larger hole the breathe box mounts the oil where the block vents itself from the baffles that are inside the breather box before going back to the block?

Or do I have it in the opposite direction? The small port is the vent, but the big port is the drain back to the block?

It is my understanding that the large port is a drain/return port, and the entire box serves as a pressure baffle for the smaller vents. By having a large size, the pressure differential is smaller and that creates a "vacuum" relative to the smaller port.

The small vents go to the PCV as you noted, and the back of the block. I'm not certain where the small block port goes, or how it is isolated from the larger block drain. I suspect it is partitioned cavity wise and one of them is subject to crankcase pressures and the other is baffled sufficiently to create a differential so it can drain and "suck" on the other ports.

Maybe a block expert can chime in.

https://www.acurapartsnow.com/v-2001-ac ... -chamber-3

The large lower port vents the crankcase into the breather box

One of the upper ports is routed to the PCV valve and then on to the intake manifold

The other upper port is connected to a nipple on one of the oil galleys. This may help vent the head some but, I believe this primarily helps ensure the breather box is always able to drain to the crankcase if the fluid volume in the breather rises above the top of the lower crankcase port. It provides the breather box an intake vent for fluid displacement as it flows to the crankcase. This is necessary since the PCV is one way by nature.

Thanks for the responses, i was thinking the same thing, now another question, will I have problems using that nipple the breather connects to as a drain back for a catchcan?

I know some people don't want to drain catchcan stuff back to the block, but right now I am currently venting my head via the valve cover bungs and only draining it back to the oil pan via the bung that devon welded on the pan he baffled for me a few years ago. (It was really meant for an oil temp sensor).

I just don't feel comfortable with the drain going that low in case it hits something on the road, etc.

I would recommend you drill a third hole in the top of the breather box, there is room. Match the diameter of the other two.
From there you can run the same grommet and plastic "nipple" as the other two, and you can have your drain without interfering with the breather box otherwise. If I recall there is room between the intake runners near where the PCV goes.