I've been exchanging e-mails with tech support at PLX. They recommend at least 24" downstream from the block for a supercharged car, mount the sensor in the top 1/3 of the pipe and point the tip of the sensor about 15 degrees downstream. I'm not quite 24" and I told them I couldn't mount it in the top 1/3 without cutting a hole in my floor or hanging my exhaust low off the bottom of the car. They replied that it was just a recommendation and to mount it as close to the top as possible. They also said it could be mounted after the cat, but that doesn't make sense to me how the reading would be worth anything after the cat. I'm going to weld in another bung a couple inches in front of the cat to give me the 24" minimum and give it the 15 degree angle the suggest. As far as being rich at idle, the narrowband and wideband would both have to be wrong for that to be happening. The only time it is running rich is at a cold start like it is supposed to.
