http://www.vortechsuperchargers.com/...95mustang.html
The"S" mean standard, but vortech also makes an "A" trim which is NOT as good as the "S" trim. The only major differences between this to trims are the impeller. A "S" trim with about 8psi boost can give another 90-100FWHP to a 5.0. <---(they claim anyway, not speaking from experience)