beef (something) up meaning

• [British slang]
  Phrs. To increase in size or volume; basically to make stronger. E.g."Once he'd beefed up his engine, his car was unbeatable on the track.”
  

• beef something up:    [American idiom]to ...
• beef up:    Verb: beef upMake ...
• beef sth up:    [American slang]to ...