Originally from the '57 Corvette SS, a race car designed by Zora Duntov. Eventually applied to the Impala and Nova, then the Chevelle, then the Camaro and the Monte Carlo, etc. Alawys the biggest and most powerful version. Now being abused by Chevy. The have a Malibu wagon with a 240hp V6 that they call an "SS." And don't even get me started on the Cobalt.
The only good modern Chevy SS models are the Monte Carlo and Impala SS, the Silverado SS, and the Camaro SS. All others (Trailblazer, Cobalt, Malibu) suck.
Old Super Sport (SS) motors-
425hp 409c.i. V8 w/ dual quad carburetors
375hp 396c.i. L78 V8 w/ solid lifters
450hp 454c.i. LS6 V8 w/ big Holley double-pumper & alum. heads