hey folks, approximately what difference will one see when measuring afr at test pipe vs tailpipe ? considering that the exhaust is straight-through, no cat, no resonator

 

Depends on if there is an exhaust leak but if no leaks then probably 0.2-0.4 and you will need to remember the reading is slightly delayed from where it would be if you had it in the downpipe

 

I added a copper extension to my tail pipe sniffer, so in my case, the readings are as accurate as in the downpipe assuming no leaks.

Almost all cars that I tune are off of the tailpipe.

 

On a 100% sealed exhaust system. You will see little to NO difference. I tuned a car with a one piece TBE and AFR's were identical. Even at idle. Most have minor leaks and I usually see .5afr leaner at the tailpipe.

I generally see about a 2-300rpm delay in AFR readings at the tailpipe from the distance between the sensor and the engine.

-Jamie

 

+1

 

What about the delay if the sensor is in the factory rear o2 location?

 

Probably between 100-150rpm delay at most. Generally not significant enough to bother compensating for when tuning. It's a horrible distance if you ever wanted to use the narrow and O2 simulation feature like Zeitronix and some other companies offer. For that to work properly, I suggest 18" from the turbo outlet and no further.

-Jamie