Are most catalytic converters directional?

[yukon]

I bought a bosal for my 240sx with no arrow so I assumed direction did not matter. have had low back pressure and high nitrogen emissions since i installed new cat. othe emission gasses are doing ok.

[projectRDM]

Random Technology cats are directional for certain, though I don't know about other suppliers I'd say it's a good bet the Bosal unit is too.

[slider2828]

I know catco's are directional..

[Pacman]

Good thing to keep in mind when they can be installed either way: put the catalyst substrate closets to the engine. If you remove it, you may notice the substrat is closer to one flange than the other. Put that side on engine side.