Quote:
Originally Posted by JFP in PA
First of all, the air box is open to the atmosphere, there is no vacuum, only flow. Check it some time with a digital manometer.
Five inches of water is the nominal value for a new, factory AOS. Higher or lower values lead to problems, so you have to assume 5 inches of water is the system's designed "sweet spot", and which is actually controlled by the AOS itself.
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flow across the end of a tube can create suction, so if the tube is introduced at an appropriate place in the airbox or elsewhere upstream of the throttle then there is opportunity for vacuum, but no idea if sufficient. note the 997.2 that appears to vent the heads directly to the intake tube while the crankcase goes to the plenum via an aos (if i am reading the parts diagrams properly).