Unfortunately, I must report that it was a bad idea to plumb my oil breather into my exhaust. It resulted in a dramatic increase in oil consumption...over a quart an hour. I used AN8 flex line directly from the breather, through an AN8 free-flow check valve, into a 3/8"NPT bung welded perpendicular into the exhaust about 8 inches before the tip (just in front of the firewall). As it made no sense that this was the cause of my oil consumption, I extensively troubleshot elsewhere. I was worried that I had excessive blow-by the rings, even though the exhaust pipes were dry (including the one with the breather).
I finally disconnected the exhaust outlet and routed the breather into a simple catch can. After 2+ hours I’d hardly put any oil in the catch can, and had consumed very little oil. I thought that maybe I was pulling too much vacuum on the engine breather and evacuating oil mist that would normally settle in the engine.
I decided to check crankcase pressure, with surprising results. I referenced the Continental Service Bulletin M89-9 which describes using an airspeed indicator as a pressure instrument. I found a free 3D printed Lycoming dipstick cap adapter here:
Lycoming Oil Dipstick Adapter
I sealed the 3D printed adapter, tapped out the hole to 1/8" NPT, and installed a nyloflow 1/4" line routed into the cockpit and attached to the airspeed indicator.
With the breather completely open, my crankcase pressures were typically 70 mph (90 max on the Continental big bore engines) until I got above 2500 rpm where the pressure peaked at about 100 mph. Normal results and I expected them to be less when I re-attached the exhuast outlet.
With the breather plumbed into the exhaust, the crankcase pressures INCREASED by nearly double! At full power I was showing over 165 mph. Somehow, instead of the high flow exhaust creating low pressure, the exhaust was pressurizing the crankcase. I can’t explain it.
So, in my case, it was a good experiment with bad results.