Can I put an O2 sensor in the h (cross) pipe?

[dandyZ]

Just wondering if I can put it in the h pipe so it gets exhaust from each cylinder bank? Does it matter?

[BRAAP]

Yes it does matter, the "H" pipe is not a good place for an O2. An X pipe would fine, but not and an "H" pipe.

 

The O2 needs exhaust "flow" over it to read what the cylinders are doing combustion wise. The H pipe doesn't necessarily have flow through it, but exhaust will move back and forth as the pressures alternate between banks. As such, placing an O2 will be measuring exhaust gasses that end up in the H-pipe over time and move back forth, not reading current or recent conditions, i.e. severe lag.

[dandyZ]

So, it's a matter of choosing one side or the other to mount the sensor... I have a dual exhaust set up on a sbc. I figured the H pipe wouldn't work. X yes, H no.

[BRAAP]

Exactly. It isn't ideal, but with only one O2 and dual exhaust, that is the compromise one makes.

 

For the most part, if the engine is running properly, all cylinders running equally both banks should be running quite similarly so its not much of an issue. On the other end of the spectrum, even running two O2's, (one per bank) is still not quite optimum but at least the entire engine is being monitored. Ideally you would want an O2 for each exhaust primary tube AND an Exhaust Gas Temp probe for each exhaust primary tube as well. But back in todays world on a mortals budget with high performance street engines, one O2 in one bank does the job quite well.

Edited July 29, 2010 by BRAAP
Typo's.