WordNet (r) 3.0 (2006):

soup up
    v 1: make more powerful; "he souped up the old cars" [syn: soup
         up, hop up, hot up]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "soup up":
   accelerate, aggravate, beef up, blow up, complicate, concentrate,
   condense, consolidate, deepen, double, enhance, exacerbate,
   exaggerate, heat up, heighten, hop up, hot up, intensify, jazz up,
   key up, magnify, make complex, ramify, redouble, reinforce,
   sharpen, step up, strengthen, triple, whet