In 1999, customers could order their SN-99 or second version of the fourth generation of Mustang GT from tuner Saleen. Saleen offered two basic versions that both had variations. The base version, or S-281, came fixed with the standard Mustang 4.6L V8 displacing 320hp all the way up to 550hp, depending on the variant. Variants included the S-281SC (Supercharged), E, and SA 20. Both automatic and manual transmissions were available. The S-351 is a supercharged 5.8L V8 pushing 500hp to the rear wheels. The S-351 also saw minimal production; only 20 cars were built in 1999 alone. In 2005 the 5th generation of Saleen Mustang S-281 replaced the SN-99.