Just thought I'd add some info:
Originally Posted by Vlad
It is almost impossible to check the function of the JDM front O2 sensor from a twinscroll against that of a USDM front oxygen sensor from a WRX.
But everyone is using them (USDM Sensors) and nobody had problems because of this.
As a note however, mine was tested by another board member and it could not be made to work on a USDM WRX, no matter how the leads were swapped. Maybe it was just defective.
This swap has been successfully done by 4 members on the board so far, via machining and adapting the crank and cam sensors, so that the USDM ECU can control the JDM engine. Either somebody is going to make available a swap kit for this option, or you will need a machine shop assistance to get the swap to work, or you modify the harness at the ECU, and understand that state computers will never talk to it, so it's a race only vehicle.
I had used the JDM O2 sensor...which just now went out. But when I threw it on with the OEM LGT ECU, I was getting crazy oscillation during closed loop. Turns out, the O2 scaling was WAY different; the LGT had a -1.3-0.74mA range vs. -13-10.9mA scale for the JDM sensor(WRX should be the same). Changed the table, and fixed that problem,
Crank sensors are the same, no issues there. Passenger side sensor bolt-hole needs to be slotted and o-ring swapped(or not; the VR o-ring is pretty thick and requires a lot of force to push in). Driver's side sensor needs to be pushed a little further back. Everybody has milled the head and use the stock sensor, but I opted for a smaller diameter aftermarket hall sensor mounted offset in the original bore(trimmed nylon bushing with a rubber washer to act as a seal under it; bracket sits on top of that and had to use a longer bolt+spacers to clamp it down). The sensor I chose is a little long and touches the TGV housing.... though seems to be working fine(Sorry for the crappy cellphone pics)!