Since I got my Y pipe a month or two ago I have noticed that the car accelerates differently...I know that it does change in lower rpms but I'm experiencing somethin else maybe...under WOT the car will start to pull fine but around 4k (i think) (mostly in 2nd and 3rd gear) it feels like it lags for a second or won't accelerate at that same rate...it's real weird and I'm almost 100% positive there are no leaks...is this normal or what could it be?? I also have a Place Racing CAI and i didn't have this happen before I got the y pipe.

 

Try resetting your ECU by disconnecting the +battery terminal for an hour or so.

 

If it's pinging, try running some SeaFoam through the brake booster vacuum hose (or some of the alternatives, like the IACV/TB vacuum hose) to clean out carbon from the engine. I did this yesterday, although I haven't followed up with a 2nd compression test to verify its effectiveness yet.