Re: Cheap exhaust
On the NA, a CAI, larger injectors and a tune will net about 50hp and noticaably better performance. The Sprint Booster will help with shifting on the 6spd.
Btw, don't forget putting 330uf caps in the doors. By far the best bang for the buck mod on an XF.
You gain nothing but noise by throwing $$$ at the exhaust.