Measuring AFR w/ Wideband

[white ZL1]

Post cat readings will typically be a bit leaner than readings taken before the cats.
I've seen anywhere from 1 tenth to 5 tenths leaner at the tailpipe vs before the cats on different cars at different points in time.

[Iam Broke]

On my '02 WS6 the post HFC reading was ~0.1 AFR leaner at WOT. At cruise (stoich) they were equal. Not enough to worry about. Only place I had to put the sensor in, no room pre cat on that setup for a second bung on the DS. Same tune same day with the same sensor replacing the pre and then post cat one in SD mode. YMMV.

[JANNETTYRACING]

Originally Posted by newb

I am not sure why its so important to go in before the cats? On the dyno. The probe is inserted at the tail pipe. Obviously well after the cats. Why can't the now useless post cat bungs be used? Since the secondaries are tuned out... Hopefully someone can help answer my question


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Cats will burn some of the left over Oxygen and there are always exhaust leaks along exhaust systems that will be picked up by a tail pipe sensor.

We only use a Tail Pipe sensor as a Last resort to Measure AFR.

Ted.

[newb]

Originally Posted by JANNETTYRACING

Cats will burn some of the left over Oxygen and there are always exhaust leaks along exhaust systems that will be picked up by a tail pipe sensor.

We only use a Tail Pipe sensor as a Last resort to Measure AFR.

Ted.

Thanks Ted. I get it that all the way to the tailpipe is the least accurate. But, in a high flow cat setup on a bolt ons car, is it worth drilling my ceramic coated kooks LTs?

[JANNETTYRACING]

Originally Posted by newb

Thanks Ted. I get it that all the way to the tailpipe is the least accurate. But, in a high flow cat setup on a bolt ons car, is it worth drilling my ceramic coated kooks LTs?

I guess it depends on how important to you, Accurate Data Is.

We do it daily, because it is Very Important to Us.

Ted.

[newb]

I wish MFRs would consider this crap when designing go fast parts. If the best wideband O2 placement is pre cat, they should install a bung there for you. Better to have it and not need it than need it and not have it. Again, thanks for the info.

Now I need to decide what I want to do.

[white ZL1]

Originally Posted by newb

I wish MFRs would consider this crap when designing go fast parts. If the best wideband O2 placement is pre cat, they should install a bung there for you. Better to have it and not need it than need it and not have it. Again, thanks for the info.

Now I need to decide what I want to do.

I'm willing to bet 99% of people that put headers on their cars don't own or have any desire to use a wideband and tune their own cars.

[StreetSS]

Ted tuned my car, which runs excellent by the way. So much so I used about 3/4 a tank driving the back roads of Virginia because I was enjoying it so much. We went through 8 tunes and the last one, I think, was to revise the tune for the difference in AFR measured at a local shop in February via tail pipe and datalogging with my new sensors installed in March. So, I would think there must have been a good amount of variance between the two measurement points. I must say that Ted worked real hard on my car to get it perfect. Feedback was always received within a hour or two of my emails. My only regret is sticking with my local tuner for too long and spending a few grand that I shouldn't have. Thanks JRE!

[newb]

Originally Posted by white 2SS/RS

I'm willing to bet 99% of people that put headers on their cars don't own or have any desire to use a wideband and tune their own cars.

I have no plans to tune my own vehicle either. But if the right way to tune is precat o2, then they should include the bung. There are very few LT installs that don't result in a tune. The most accurate tunes use/need precat o2 data (as i now understand from this thread). So its a 25 cent job added to the building of the headers but a much bigger deal after they are sold especially if they are installed on the car already. They could easily just come with plugs in the extra bungs. I would have paid an extra $10 for them to be included when I ordered.

[white ZL1]

It's really not needed.
Pull one of the front O2's, plug your wideband in, put the car in open loop, tune it, pull the wideband out when you're done, put the stock O2 back in.....and enjoy.

[Iam Broke]

One of the deciding factors on my Kook's LT's was the second bung on the bank 1 header.

Some of us like to log & tune.

[newb]

Pretty sure I don't have a second bung but I will look.

[Daniel20162ss]

If your running offroad connectors(catless), could you just use one side of the connector pipes bung to connect wideband and have the same result as adding a header bung since its straight through anyway?