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Old 11-15-2012, 10:42 AM   #26
Scooby Specialist
Member#: 268354
Join Date: Dec 2010
Chapter/Region: NESIC
Location: Massachusetts
02 WRX 05 LGT
Slow Automatics


Originally Posted by the suicidal eggroll View Post
Probably for rapid closed loop changes. The farther the sensor is from the heads, the more delay you get between combustion and measurement. This will effect the behavior of the closed loop system, enough delay and you can start to get oscillation. This has nothing to do with whether or not the measurements are correct though, just the time delay in getting them.
I'd buy that as the major reason to why the sensor is in the uppipe. I've also been under the impression with low exhaust gas flow, its readings are more stable being closer to the ports. The other thing is it probably gets up to temperature quicker there, and has less of a chance for water vapor to collect in it.
Originally Posted by NSFW View Post
For the twin-scroll cars, Subaru actually did put the front O2 in the downpipe.
Hmm, interesting.. Probably so they could get readings of both banks with one sensor. No doubt the OEM unit is a wideband, and could be used as one (besides the rich limit), I'm just saying if it were optimal to have it the downpipe (in context of stock ecu/ CL parameters, etc), all turbo models would. As far as simply monitoring AFR for your own use, putting the O2 in the downpipe is the way to go.
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