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Wow there's so much incorrect information in this thread. So in as simple terms as possible.
Cats restrict airflow. Engines are tuned to as much power as possible with the given airflow. Trying to force more power with tuning will result in bad things happening to the engine. Engines blow up if tune is bad. OEMs rarely leave power on the table for NA engines, which is why tunes and bolt ons without tunes gain little to no power. They are as good as you can get for factory equipment. Big company doesn't spend hundreds of millions on RnD for a 500$ piece of metal to randomly do better or a random company to tune better without sacrificing something. That's why stage 1 tunes do little to nothing on our cars.
Properly designed equal length headers will always be superior to UEL.
The torque dip is a result of the short length headers and the cat creating bad airflow in the mid RPM range. The above two points are proven by the ACE350 and JDL 421 equal length headers proving better power across the board over the vast majority of other headers. ACE350 has a peak where the valley was before. Both are catless.
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