A/F Ratio Question

[givemeaboost]

I just redid the downpipe on my homemade frontmount system and went down into the tunnel instead of routing all the way out the back. My downpipe is only 2'' dia. so I weded the bung in with a 1/4'' spacer behind it so the oxygen sensor wouldn't be sticking so far into the downpipe causing unnecessary backpressure. The a/f now reads way lean(went from 11's to high 13's) and I 've jetted up twice since. I'm now running 143.8 mains at 17# boost with high 13's a/f. Is my sensor just not working right because it's not far enough into the heat source or what?

 

[HURRICANE]

I think that you have to believe the o2 sensor.If it wasn't hot enough, it wouldn't work. My thought,,with your down pipe,you are leaner because of less back pressure allowing a cleaner charge into the engine,I would jet up till you see results and you should make more power as a result

 

[rxrider]

I better watch my AFR #s as I'm jetted 132.5 right now. I had a MCX rear mount system last season with the sensor in front of the turbo. Now I'm running NFS2's turbo header a PL prepped GT2860RS and 2" x 3.5" double downpipe, guess backpressure will be dramatically reduced over the MCX rear mount....

givemeaboost - Thanks for posting your results
HURRICANE - thanks for the advice

Will watch the AFRs carefully when I wake her up.

 

[zross1]

Is this testing done on the mountain at elevation? Or in the garage? I think you Mt guys have enough to ride on now I had a gt2871 Boondocker kit and custum made 2.5" exhaust out the side panel (not much back pressure at all) 127.5 mains 17 psi and I was mid 12's.

 

[givemeaboost]

My testing was done at the grass drags at 65 degrees and 3300ft elevation. My best time was a 5.95 run for 500 ft.