"After the cat, it flattens out into a section dubbed the infamous "U-Bend," which is a section of pipe crushed into a "U" shape by GM in order to fit a rear O2 sensor. This section has less volume than the same length of 2" pipe, and approaches the volume of a 1.75" pipe with the rear O2 sensor in place! Our bolt-in downpipes eliminate all of the aforementioned problems! Gains of over 15HP have been seen, along with a substantial drop in knock. Most users can drop a pulley size and/or eliminate 5-7 degrees of knock."
For a lousy 213.00 (that includes both front and rear gaskets AND a cat!) you can't go wrong, replaces U-Bend and is a direct bolt in. I will be ordering mine next week.
Here is a good picture of the dreaded U-bend