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Well, I can't advise you to go afoul of emissions laws . . .
How some people modify their H3s depends on the year of the H3. In 2006, both cats were monitored by O2 sensors. One before the first cat, the second sensor behind the 2nd cat. In 2007 and newer, only the first cat is monitored and some people have been known to delete the 2nd cat. You do need to have the monitored cat(s) in place or your H3 will not run properly as the sensors need to see a difference in readings between the two cats. Maybe it's possible to delete the 2nd cat in a 2006 and still have the H3 run properly, but I have not seen that tested.
If it's the first one, that typically requires a new exhaust manifold as you would not be able to replace that cat independently of the manifold.
How some people modify their H3s depends on the year of the H3. In 2006, both cats were monitored by O2 sensors. One before the first cat, the second sensor behind the 2nd cat. In 2007 and newer, only the first cat is monitored and some people have been known to delete the 2nd cat. You do need to have the monitored cat(s) in place or your H3 will not run properly as the sensors need to see a difference in readings between the two cats. Maybe it's possible to delete the 2nd cat in a 2006 and still have the H3 run properly, but I have not seen that tested.
If it's the first one, that typically requires a new exhaust manifold as you would not be able to replace that cat independently of the manifold.