or buy a rebuilt they are dirt cheap. i have seen some go for under $500 on ebay...with warranty. used one from a boneyard should only be about $100-$150.
2003 Ford Expedition: 5.4L, harley supercharger, 2.93 upper pulley, 4lb lower pulley, c&l plenum, jlp cai, LFP SBTB, FTSP, Magnaflow 3" catback, Eclipse AVN-5510, white face gauges, cobalt c2 boost gauge, ddm hid's, 379 rwhp, 465 rwtq sold 11/3/12
2009 Ford Flex Limited AWD