afr, where to measure?

[bscottie]

I have a afr gage in my car, instructions say install the oxygen sensor in front of the cats which I did, I have been on several different dynos, some want to measure the afr before the cats, some measure from the tail pipe, which is better, does it really matter, how close are the readings? any thoughts? I have seen people post afr on FI cars anywhere from low 11s to mid 12s, what is the best? is there a best

 

[don_w]

The closer to the header collector, the better. A tail pipe sniffer will likely read 1/2 point higher or so.

 

[Freaknazty]

the best would be 11.5 afr and 12.5 n/a correct ? i was told the closest possible place to put it to the merge collector the better

 

[Royb]

one thing most people overlook is the sample rate that is measured with a a/f gauge. when data-logging use 3 sample rates so you can truly understand what the a/f ratio is. 12.5 is an ideal target. I ran 12.5 - 13.3 & never had a problem.

like everyone said the position is ahead of the cats near (1-2 inches) the collector.

 

[Androdz]

n/a 12.5 is somewhat rich. I ran n/a at 13.5ish with no probs makes a little bit more hp aswell