I am not saying you cannot tune w/a narrow band, it's possible & has been done for many many years.
It's just the narrow band is so slow in response time your A/F ratios could be way off @ especially during gear shift points.
I did tune my Syclone w/a narrow band O2 & w/that (narrow O2 sensor) I had the worlds fastest stock turboed Syclone, for about 8 years. I had no extra cash to get a wideband.
I did have a reading problem during the shift points though, the narrow band would show full rich @ the top of each gear change (thinking it was fine) but actually was dangerously lean,there was a couple second delay with the readings w/the narrow band O2.
I now use an old Innovate LM1 unit on the Syclone. It was not until I wanted to turn up the boost & lean on it a bit more, (lean it out)I would only feel comfortable doing this with a wideband. I could have done it w/a narrow band,just much safer w/a wideband IMO.
Guys still tune there Buick GNs & Regal T-Types w/there stock narrow band, getting advise that has been passed down from older owners, there were so many of those cars made it's pretty easy to get good info on what works & what does not work & what's lean & what is rich, all measured in millivolts w/there scan tools. One of the main reasons I tell guys to get a wide band O2 is to speed up the tuning process, most times you do not need to take out your plugs to look @ them.
It would be absolutely essential to get a wideband when you are forced induction, being too lean will destroy an engine very quickly & a wideband takes away the guessing, you know exactly when it's too lean or too rich right there & right now.
When I had the Paxton superchager on my inline 6 I did it the old fashion way, I jetted it richer right off the bat as compared to my normally aspirated set-up. Took plug readings (a lot) It was a somewhat long process tuning 3 DCOE's, but hey I learned.
