Anyone run high-flow Cats to reduce hydrocarbon exhaust smell?

Second the vote for cats and running a downstream.

While they can and do function well with only the upstream, this is not reflective of the capabilities of the system as a whole.

The downstream sensor's primary function is to check the function of the catalyser but it also imparts data (at least in OE systems) to help with the modulation of air/fuel ratios.

It may be a good idea if you're thinking of this to either read the data sheet and tech manual for the injection setup, or contact the manufacturer directly. This will let you know if running a downstream sensor is beneficial and you can go from there.

- boingk