Originally Posted by Fully_Bolted
To make things even more interesting- since the factory o2's are post turbine, that certainly has to effect things if you are trying to time the exhaust pulses down stream in a preturbo o2 design that also has WAY less back pressure.
Yes this was exactly the thing that made me think they couldn't possibly be doing this, but then I kept reading and it looked like they were. The HPF folks seemed to discover this empirically the hard way. However if I remember correctly it is only key to keep the streams read by the first O2 sensors for each bank separate, as Shiv did, and somewhat close to the exhaust port in terms of length not so much that it is pre or post turbo. So who knows lot of mystery here.
If you think about it you can still hear clear exhaust pulses out of an exhaust, so even after getting scrambled by a turbine wheel (or wastegate) and six cats there is a distinct acoustic signature for each cylinder in terms of information content available. So I would bet the times series read out of an O2 sensor still has distinct info available for reading out of each cylinder's combustion byproducts.
I doubt any of this is going on all the time, there are probably fixed steady state or cruise conditions that kick off a measurement/ID cycle.