- 1). Park your STI and make sure the engine is cold. At the center top of the engine you will see the intercooler, a large metal heat exchanger that looks like a radiator. Connected right off the intercooler on a plastic hose is the factory bypass valve (BPV) connected to two hoses (one large, one small) via metal clamps.
- 2). Remove the factory bolts that hold the BOV to these hoses using a 12mm socket, then remove the BPV. Use the plug included in your BOV kit to block the larger of the two hoses. The larger hose was the recirculation hose which routes air from the factory BPV back into the intake manifold.
- 3). Install your BOV into the factory location, re-using the factory gasket from the factory BPV. Connect the small factory hose to the BOV with the hardware supplied with your BOV.
- 4). Periodically check the bolts around the BOV to make sure all connections are tight between the intercooler and the BOV.