I have a question regarding the use of a wide band and catalytic converters. On my 96 TA I don't have cats and I also have an O2 bung welded in after the headers for my LM1 wide band, this way I can have the most accurate A/F ratio readings. Now my question is I have a couple friends that want to go to the Dyno and have me adjust there A/F ratio but they still have catalytic converters on there car. Do I need to have a O2 bung welded on to tune them or do I just use the A/F reading with the cats on? I am just not sure how the cats affect A/F ratio.

 

you should put the wideband o2 close to the front as possible, you dont want to be measuring after the cats

 

Cats will affect 02 readings up to around 4K RPM. After that, a stock cat cannot compensate enough and thus the AFR will read essentially right on.

 

That's quite interesting. This makes me consider buying a tail pipe O2 sensor clamp for my LM-1. Innovate has instructions on not using the tail pipe clamp for catted cars though. As you say, it is after 4k rpm that the cats have no effect. My a/f read-out from the dyno pull starts at 2200 rpm with a few upward spikes around 3300. After that it's a smooth slope downward.