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Old 02-03-2007, 12:24 AM   #1
shemoves
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Default Are catalytic converters directional?

I need to switch the Legacy's around so that the O2 bung is on the pre-cat side, rather than on the post-cat side. Wondering if the direction exhaust gas flows through the cat matters...
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Last edited by shemoves; 02-03-2007 at 01:49 AM.
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Old 02-03-2007, 05:18 AM   #2
06grayrex
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I believe the o2 bung should be before the cat, but I do not think if you had a cat that was universal it would matter what direction it should be installed.... Please correct me if I'm wrong......
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Old 02-03-2007, 12:26 PM   #3
shemoves
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yah, o2 needs to be pre-cat (unless it is the one that OBD-II cars have that is specifically for measuring post-cat air quality.

All it is as far as I know are mesh screens (retains/builds heat, cooks the junk out)...someone has written 'top/flow' with an arrow on it though so it made me wonder.
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Old 02-04-2007, 11:05 AM   #4
IllNastyImpreza
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I know the 1st o2 is before the 1st cat. and I'm pretty sure the 2nd one is as well....

as far as universal cats...I'm pretty sure it doesn't matter. I just replaced my front O2 and rear cat.
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Old 02-04-2007, 08:55 PM   #5
NWstiLTD
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as to the o2 sensor question, the upstream sensor is for fuel mixture, the post cat sensor is there to measure catalyst efficency only and must be located after the cat.

I am not sure about directional cats. I dont see why it matters, you have a honeycomb that gets hot and why it would matter which way the air went is beyond me. There may be some engineer who would disagree, but if you want to hook one up backwards I cant see any problem that would result as long as the sensors remained on the same side of the cat that they were on before the flip
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Old 02-04-2007, 11:03 PM   #6
shemoves
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Quote:
Originally Posted by NWstiLTD View Post
as to the o2 sensor question, the upstream sensor is for fuel mixture, the post cat sensor is there to measure catalyst efficency only and must be located after the cat.

I am not sure about directional cats. I dont see why it matters, you have a honeycomb that gets hot and why it would matter which way the air went is beyond me. There may be some engineer who would disagree, but if you want to hook one up backwards I cant see any problem that would result as long as the sensors remained on the same side of the cat that they were on before the flip
That is the same conclusion I came to.
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