''...A sleeper (US English) or Q-car (British English) is a car that has high performance and an unassuming exterior. Sleeper cars are termed such because their exterior looks little or no different from a standard or economy-class car (or in some cases worse due to seeming neglect on the owners part), but internally they are modified to perform at higher performance levels. The American term possibly comes from how an aggressive animal can seem gentle or perhaps friendly until awoken, while the British term may derive from the Q-ships used by the Royal Navy, or the fictional character "Q" from the James bond 007 series.
The earliest known reference to the term 'Q-car' is in the February 1963 edition of Motor Sport magazine (published in the UK since 1924). The editor, Billy Boddy, said of the Lotus Cortina ~ "...the modifications carried out by Lotus have turned it in to a 'Q' car par excellence...".
Its not really about just straight line performance, its a whole lot more. 1/4 mile is pretty pointless for a car than can corner better than a fast straight line car.