[sarotara]

As HeMi101 mentioned, the GMPP handling kit would help with handling. If you do not want to spend a lot of money and keep the car naturally aspirated install a downpipe and the GMPP dual exhaust. The downpipe will eliminate the restrictive U-bend that's in the stock exhaust. You can also install a fenderwell air intake. These are the simple and cheap mods. However, as I mentioned before, Impalas are not really race cars, and you would really be better off getting a different car instead of spending a lot of money on doing engine swaps, etc.