The system I saw in use pulled 0.5 bar pressure at speed from the crankcase of an otherwise sealed engine block (dipstick replaced by rubber plug etc). The way it works is the same way as the venturi on an old Piper. The fast flow of air through the venturi drew fumes out and thus pulled oil BACK through the tail of the crank. There is a venturi in the exhaust where two pipes come into one at a Y-shaped joint. I can't decide if the little pipe needs to go at a piont of largest cross section or soewhere else. There is an antibackfire valve from a brake servo in the system to stop a tailpipe backfire from igniting the oil vapours in the crankcase.
So.....Do I need the little pipe at the point of largest cross section and does it need to point downstream or at 90 degrees to the flow.
Has anyone got a pictur of a venturi off an old Piper????