I know the reading from a tailpipe sniffer wideband is delayed by some time from that read by a wideband in the ideal location just downstream of the turbo, but has anyone done a definitive experiment with two widebands to see what the measured a/f differences are pre and post catalytic converter? I know a lot of dyno tunes are done with just a tailpipe sniffer, but I was hoping to get an idea of how much this kind of tune might be in error.

Thanks!

Mark

Please don't take my word for it, there are better sources than me on this forum. But I would think that once the exhaust gets far enough downstream to cool enough that it is no longer is burning, the AFR would remain consistent in a closed (well, open at the inlet and outlet only) system like an exhaust pipe.

I got protuned this past weekend and for most of the people, he was using a tailpipe-mounted LM-1 setup. On my car, he used the LC-1 that I have mounted in the downpipe of my APS exhaust. He remarked that "it will read a bit richer". Not much else.

Interesting. Thanks for the info!

Mark

The consensus I got from experienced tuners a few years ago was that it simply doesn't matter for WOT/power tuning.

Tuning low load areas is a different story, but even then they are pretty damn close.

I've had the two reading at the same time. The difference is negligible and could be attributed to the widebands just being two different units or a delay in reading. For WOT the exhaust velocity is fast enough so that they will read very similarly. Part throttle and cruising you will see a difference due to delay but even that will be slight. At least in my case with one cat between the sensors the AFR didn't change.

Thanks again, guys. CDVMA, that is exactly what I wanted to hear. I figured that at WOT there wouldn't be much difference, but it's great to hear actual concrete evidence of that.

Mark