Sleeper cars by definition, give you no indication of any performance tuning done and that is largely down to its almost factory appearance.
Small changes like the fitment of an aftermarket wheel and a drop in suspension are probably the only tell-tale signs to suggest a bit of tinkering has taken place.
Supercars beware
A perfect example of a sleeper is the 1970 Chevrolet Pickup truck in the TV reality show Street Outlaws. While its appearance looks rugged and somewhat disheveled, under its bonnet is a custom-built V8 engine fitted with a high dosage of nitrous racing unsuspecting drivers.
WATCH: Corvette, GT-R, Hurracan vs... a Honda Insight?
As the video clip below shows, a couple of high-end performance get the surprise of their life when innocent looking cars come out of nowhere and show them a few things.
Check out the video: