I have a venturi gas vacuum pump on the the end of an exhaust as an example. The exhaust spills out at 2.5cfm and 2 lbs. On a average of venturi efficiency, how much cfm at what pressure (or ratio alike) would be needed to eject the exhaust gas to near vacuem? As a secondary question, what would evacuate the exhaust faster, a high pressure low cfm input, or a low pressure high cfm input? As a third question (sorry for so many), how would the venturi effect the sound as the exaust is lowered in temperature and pressure and then gained in pressure?