I am installing an SLC Free B wideband controller which uses a Bosch LSU 4.9 O2 sensor. That sensor has an operating temperature of 740 to 820 with a perfect target being 780. The company (14point7.com) sells a version "C" (although, harder to get, maybe discontinued) which uses a different O2 sensor (LSU 4.2) whose range is lower, and perfect target temperature is 750 degrees. Right off the bat, the over-lap of the ranges makes the decision hard, but, I've got the 4.9, not the 4.2, so that is what I will be using. My downpipe is an HKS original... to my knowledge, the one that all the others are copies of . The mounting boss in the HKS pipe is about 8 inches behind the turbo (7mgte) and the instructions for the SLC say the sensor should be before the cat and 36 inches behind the turbo. I have two weld-on bosses coming and plan on having them welded in at two feet and 3 feet, and to plug the one I don't use (as well as the original). Frankly, 780 degrees of heat in my downpipe sounds insane, but, surely the designers know something about it. Short of trial and error, how would YOU position this sensor considering the facts and requirements? It also has to be on the pipe between 10 o'clock and 2 o'clock. That might not sound like a problem, but, the engine has been on the stand for so long that I have no idea what the clearances are two and three feet down my front pipe Anybody have productive advice for me?