Portable wideband setup. Does Cats effect?

Hey guys, if I would like to run an exhaust clamp style of wideband setup, will this give incorrect readings with catted cars? If so, is the only way to tune catted cars replacing the oem o2 sensors with wideband ones then unistalling?

Cheers

While it may make a slight difference, at wide-open-throttle (WOT) tuning (rich mixtures), there is no difference. If you were trying to tune a street car cruise, it might read slightly lean, but only say 1-3% so I wouldn't worry about it. Using a tailpipe clamp is difficult to tune idle as the free air make it tend to read extra lean (I sometimes cover my hand over the exhaust pipe and see how much the reading changes.

As David said, the further up the pipe you can get the sniffer the better, and there are "test pipes" which temporarily replace the cat' for testing - doesn't help if it's checking customer cars, though.