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A closer look inside the compressor inlet reveals the attention to detail of Borg Warner's engineers. Notice that the discharge slot of the integrated bypass valve aims right at the compressor wheel. This wasn't an accident. During instances of closed throttle, the bypass valve opens to shoot high pressure air through this port and at the compressor wheel. This utilizes the recirculated air to help retain shaft speed as opposed to wasting it by venting it to atmosphere. Every little bit counts.
However, the Borg Warner EFR 8374 comes with an integrated bypass valve, we replaced ours with a Turbo Smart Kompact Dual Port. The Kompact dual port is manufactured from billet aluminum and has a piston type valve inside that eliminates the risk of a diaphragm rupturing and is able to easily handle 30+ PSI of boost pressure. 
The Turbosmart Kompact earned its “dual port” name by having two ports which allow it to fully recirculate, vent to atmosphere, or a progressive combination of both. What's cool about using a combination of the two, is that at low boost pressure the Kompact will recirculate up until 50% valve lift before venting to atmosphere. This keeps MAF sensor equipped cars like ours happy at idle and low RPM. At high RPM and boost pressures, the second port will open up to double the amount of available flow.
As demonstrated by our lovely resident hand model, the ratio of recirculation to venting to atmosphere can be adjusted on Turbosmart's Kompact BOV by simply rotating the head. It sure smells like zombie ass up in here…
Getting back to the Borg Warner EFR 8374, the more significant finding that'll result from a gander inside the 4″ ported shroud compressor inlet, is the aerodynamically efficient design of the compressor wheel. The compressor wheel inducer measures 62 mm in diameter and expands outwards to an 83 mm exducerer (or major diameter).
