I've never looked, do X150s have both Upstream AND Downstream O2 sensors? That would create quite a problem.

 

Yes there are 2 but no issues observed. I did a baseline before and after and no horsepower difference the only difference I saw was torque increased by nearly 50 ft lbs be that may be due to the ambient temperature being about 40 degrees lower after the cats were replaced.

 

Not certain how accurate the data is but it looks like 14.4 with factory cats and 15.5 with the 200 cell cats.