Test Pipe or HFC?

FuTuRe is Z · 06-17-2014, 01:50 AM

I always wondered where tuners take the AFRs readings from, a sniffer on the tail pipe or from the O2 sensors on the vehicle.

I'd imagine that if you had a j-shaped O2 bung it would read slightly leaner than if the bung where right inside the test pipe. Therefore you would tune with a bit more richer AFR to offset that.

I'm pretty sure people using J-shaped O2 bungs on there test pipes are leaving power on the table because the O2 sensor is getting an in accurate AFR. Correct me if I am wrong here.

brancky3 · 06-17-2014, 08:07 AM

Quote:

Originally Posted by FuTuRe is Z

I always wondered where tuners take the AFRs readings from, a sniffer on the tail pipe or from the O2 sensors on the vehicle.

I'd imagine that if you had a j-shaped O2 bung it would read slightly leaner than if the bung where right inside the test pipe. Therefore you would tune with a bit more richer AFR to offset that.

I'm pretty sure people using J-shaped O2 bungs on there test pipes are leaving power on the table because the O2 sensor is getting an in accurate AFR. Correct me if I am wrong here.

The second O2 sensor is on the test pipe / HFC, the first one is on the header (right?). AFR readings are only taken from the first sensor, the second sensor is merely a check to see if the cat is doing its job.

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06-17-2014, 01:50 AM	#1 (permalink)
FuTuRe is Z Enthusiast Member Join Date: Nov 2013 Location: CT Posts: 263 Drives: 2014 370z Rep Power: 13	I always wondered where tuners take the AFRs readings from, a sniffer on the tail pipe or from the O2 sensors on the vehicle. I'd imagine that if you had a j-shaped O2 bung it would read slightly leaner than if the bung where right inside the test pipe. Therefore you would tune with a bit more richer AFR to offset that. I'm pretty sure people using J-shaped O2 bungs on there test pipes are leaving power on the table because the O2 sensor is getting an in accurate AFR. Correct me if I am wrong here.