Flows much better than the stock part increasing HP and reducing possible KR. This product can come with or without a high flow cat. Anytime the OEM cat is removed and a high flow cat is installed in its place there is an increased chance of setting a check engine light. If this piece is ordered without a cat, then it is intended for an off-road vehicle and will definitely set a check engine light. A tune is not required but highly recommended. Will fit your GXP or Redline kappa chassis car.