1) Can you install the upstream O2 sensor in the provided bung on drivers side with it only reading 1 cylinder, would it be a problem? Or, Must you install it in the collector? Se pic below





2) If you cut the flange between the #6 and #8 cylinders, as seen in picture below, to facilitate installation and removal without having to remove coolant temp sensor, will you have issues with exhaust leaks?



Thanks for any responses!

 

AS you point out the read from one cylinder coudl be problematic. You will get a better read when all four cylinder gases "mix" in the collector.

 

O2 should be in the collector or as close as possible where exhaust pipe attaches to header. O2 sensor on 1 tube will have fuel management base on 1 cylinder. Possibly leading to fueling errors on other 7. The split header flange depends on its thickness. The thicker flange is less likely to leak.

 

As you know, I experienced a problem last summer when my #8 primary came loose and then cracked near where it meets the collector. My header had the gap in the flange you're asking about. However, one of the two bolts on that primary (the inside one nearest the #6 primary) was missing altogether, and the other bolt was loose. That remaining bolt is also not in a bolt hole in the flange per se, but rather a slot. So undoubtedly then inside bolt went missing, which made it easy for the primary to work its way out of the other bolt because of the slot. I should note two things: 1) that gap was cut in the flange by Hooker themselves on that pair of headers, not by me or the previous owner; and 2) those headers were on the car in good shape for about 15 years with zero issues until this happened.

The big takeaway, to me, is to check your header bolts! If I had done this each spring I'm sure I would have caught this and tightened them and still be going strong on the original headers. It's true that if the flange were continuous I would not have had a breakage, but I still would have had to replace the gasket at the very least once those bolts loosened up. Also, it was recommended to me to use Remflex header gaskets (IBVETN2, our mutual friend). The big advantage of these is that they never permanently crush, meaning the header bolts should never loosen up over time. I am using these, and so far they work as advertised. I'm still checking the bolts periodically, though!