First of all hg is Mercury.
15hg means nothing without a unit of length. The 15mmHg would be the amount of pressure to support the pressure of a cylinder of mercury 15mm high. Millimeters are the standard unit for vacuum as the scale is finite from 14.7-0. You may see pressure in other units since the maximum pressure is infinite.
The pressure in an intake consists of two components, the static pressure and the velocity pressure. A pressure tap that is perpendicular to the flow in a fluid stream will read the static pressure component only. A pressure tap that is parallel to the flow will read both components.
Ryan’s catch can is supposed to do three things.
- Vent crankcase pressure.
- separate the oil out of the crankcase gasses.
- Provide additional differential pressure on the rings.
Even 15mmHg is only 0.290 PSI. This is Nothing. The cylinder has 500+ PSI during combustion (35 bar) to seat the rings. Venting to atmosphere with the catchcan would give him a differential pressure of 500-14.7= 485.3 psi on the rings.
With the added benefit of the catch can he will have 500-(14.7-0.290)= 485.59 psi to seal the rings.
Clearly this massive 0.06% change in ring pressure will not make a difference.
Actually if you had a perfect vacuum, you would only have 14.7 psi additional on the rings, this would only be a 2.8 percent increase in ring sealing pressure. And this pressure does not really translate to a 2.8% increase in sealing. once the rings are sealed, they are sealed. This is why they make low friction ring packages, as the cylinder pressure is far more than sufficient to seal the rings.
The only real purpose of the catch can is to prevent the buildup of combustible gasses inside the crankcase. The best way to do this is to draw a slight vacuum from the intake. YOU NEED TO POINT THE VACUUM HOSE AT THE TURBO. This will provide more vacuum than the static pressure would indicate. (this is how the Moroso unit works BTW)
:thumbup