Air leaking INTO cat - any emission effect?

[tom h]

Would tailpipe emissions be affected, if the joint between the downpipe and cat inlet is loose? This might allow air to aspirate into the cat, under some circumstances.

As I understand it, some aftermarket downpipes require a loose slip-fit at the cat, not a crimped fit.

note: Los Angeles county emissions testing.

[gofstbuick]

An air leak in front of the cat may affect NOx emissions. The reduction bed is in the front of the cat. That bed requires no oxygen to reduce NOx. If there is excess O2 in the front protion of the cat, it may promote combustion. The temp increase (from promoting combustion) may create excess NOx.

[tom h]

Originally posted by gofstbuick
An air leak in front of the cat may affect NOx emissions.

Thanks!

Seems the safe thing to do, is use a non-deforming band clamp on the front cat connection.