Evening all, I have purchased a secondhand pair of cats for my 4.0 1991 car. This is the part that fits straight on to the exhaust manifold and contains 2 round cats. The actual downpipes are the same part number but the lamba sensors are different. The cars original is a Bosch one that is quite large but the replacement has one that is slightly smaller in diameter. Will this have any impact on the performance or will I need to change them over. Both have 3 wires coming out and the same plugs etc? Any help greatly appreciated.

 

A bit of research solved this. One was the original Bosch Oem the other is an aftermarket replacement. I will switch the Down pipes and take it from there.