There will also be a little delay between them due to distance.

 

sniffer is no were near wideband... more closed to the accuracy of a narrowband

 

several reasons...

there should be a constant drop across the cat which can be calibrated.

cats only work at stoich, tuning is not going on under stoich conditions.

the tail pipe is an estimate.

 

Recently during tuning.. I compared values from my LC-1 mounted in the downpipe, and my tuners Autronic exhaust gas analyzer mounted in the tail pipe. My exhaust is 3" AMS downpippe and RC Dev 3" decat and cat back.

The LC-1 read about .3 AFR lean at idle... and then about .3 AFR rich at full boost (compared to what the Autronic read). If you don't have any leaks in your exhaust... I'd really like someone to explain how the tail pipe mounting is less accurate?

Based on the above results if I ever use the LC-1 for tuning I will deffo be on the safe side in terms of fueling.

Some of the most expensive analyzers like Autronic come with kits for mounting in the muffler. If it was not appropriate they wouldn't sell with the clamps and such.

As for delay, yes I'd agree it probably is slightly slower... by whatever the time the exhaust gas takes to travel 10 feet or so... which I'd doubt is very long.