I think that most people do the driver side cause its the most convienient. Those are for Cylinders 2 and 4. The passenger side is 1 and 3. It just depends on where you want it. I hear that Cyl 3 runs the leanest so many people go through the hassle to pit it in that one. IIRC, it really doesnt matter but I, personally would put it in the passenger side.