a have a cat-back exhaust and downpipe on my car and recently added a test pipe and ever since i added a test pipe when i am in 4th gear at WOT around 6k rpm to redline it sounds and feels like it is sputtering and it continues to do it when i get into 5th gear at WOT at around 5k rpm through redline. has anyone else had this problem? i am going to AMS tom to get a base flash i am going to ask them if they know anything about this.

 

did u get the car tuned after the downpipe test pipe and catback install? cause if not, your boost would spike like a ****, and the sputtering you are feeling is the car cutting boost and you feel the loss of power as "sputtering"