When tuning a car on a dyno, tuners use the sniffer in the tailpipe, right? People tune cars with and without catalytic converters, right? Then why the hell does everyone make such a big deal out of putting the WB 02 before or after the cat? Has any ACTUAL testing been done to confirm there is a difference? From what I have heard, it's not even .1 afr difference. I wish I had logged before I went to a test pipe ( literally JUST started being able to log). However I don't see a difference looking at the guage.

Does anyone have conclusive evidence on this? I'm curious to see hard facts, and to the armchair mechanics, cool it. I'm not looking for speculation.

-Doug

 

I guess that's the sweet spot for the gases.

 

For a catted car, it might make a difference. Most of the dyno runs you see are more than likely with a test pipe. And in that case, I don't think it makes much difference. Now the angle at which you install the bung relative to the horizon does make a difference but if it's test piped, then it doesn't matter really.

Most people, including me, put it right at the end of the downpipe for ease since there is a grommet you can push out and feed the sensor cable to the inside of the car.

 

I see what you saying, but my argument is that people seem to scream and shout whether the sensor is put before or after the cat. My point is, I don't think the cat has any effect on the reading.

 

I highly doubt that 98% of cars dyno'd are catless

that's just a silly observation

tuners don't solely rely on afr's when tuning...although I'm sure there is a suggested addition/subtraction afr method for a catted car when using a tailpipe sniffer

 

The further downstream the Wideband the less accurate the reading is.

 

idk mine is right before the cat and its just fine for me and thats how it will
stay