Wikipedia defines a sleeper car as a car with high performance and an unassuming exterior.
Unassuming exteriors do not come any better than the specimen we have here, a Lada 2104 Estate, an old eastern-European workhorse mostly known for its general crappiness. No man in his right mind will ever assume that going fast is one of the talents this Lada has.
But thanks to various Silvia S13/S14 parts, including the SR20DET engine tuned for 400PS, this Lada can run the quarter mile in low 12s, sprint from 0 to 62mph in just 4.6sec and hunt down snobby Porsches looking for easy prey as the video from SpeedNation.tv vividly demonstrates.
Sleeper cars are cool, sleeper Ladas are always hilarious though.