Breather tube reduction

[CharlieWaffles]

I recently came across a air/oil separator for io-540s but it has a 3/4" input and output. The breather tube connection in my yio-540 stock from vans is 1". Seems to my limited engine knowledge that reducing the breathing tube to a smaller size could create higher pressure to the crank case. But perhaps the air/oil separators are all this size and the reduction is no issue. Can anyone shed light on this to me?

[vlittle]

Originally Posted by CharlieWaffles

I recently came across a air/oil separator for io-540s but it has a 3/4" input and output. The breather tube connection in my yio-540 stock from vans is 1". Seems to my limited engine knowledge that reducing the breathing tube to a smaller size could create higher pressure to the crank case. But perhaps the air/oil separators are all this size and the reduction is no issue. Can anyone shed light on this to me?

Odd, I just went through this very question. I have a Raven 1/2 inverted air-oil separator. Input is 1" hose, return to sump is 3/4" hose and overboard vent is 3/4" (could have been a 1" if I'd ordered a larger fitting).

Raven site says that it's acceptable to reduce the breather to 3/4" for an IO-540. With all of the separator gobbledeegook between the engine breather and the overboard breather, I'm not sure of the airflow dynamics. Also, I think total length matters.