There are many reasons to replace or modify your existing exhaust system; whether you’re looking to gain a better exhaust note, performance, or even clearance.
Replacing the whole exhaust system does make sense as it would be one whole unit by one brand as opposed to two separate brands, or two different styles of exhaust systems. The biggest reason to replace the cat-back is because you don’t have to get involved with removing or replacing the cat.
In most states, post emissions vehicles require the use of a catalytic converter, and swapping to a full system may eliminate it meaning Johnny Law will do his best to keep your rig off the road. This may not be the worst case scenario for you guys and gals who intend to stay off-road, but for those looking to drive their Jeep to and from work, school, or even to the next mud pit it can be a major pain in the neck. Buying a full kit with cats can also be considerably more expensive.
That being said, you might also wonder how well these kits sound and perform. They may still be a bit choked by the cat, although their design allows for them to provide maximum flow rates.
Paired with a proper set of headers makes for a flow rate only topped by outlawed setups. The muffler is where most of the sound is coming from, and as long as there is a muffler, no matter how aggressive, you’ll be steering clear from the law. For the most part. This means you will still get the low rumble you’re looking for.