Any muffler with a wider exhaust port that allows for a louder sound. Typically found on cars owned by drivers who can't afford a real street-racing car but want to act like they have one.
Fartcans are installed on cars strictly to make noise to annoy other drivers.
An exhaust found on a typically shitty car owned by chavs, such as a Corsa B or a 2004 A3. They make a horrendous sound and make the driver look like a complete idiot.
Jon: Listen to the sound of this bad boy, just stuck it on my new Corsa B
Dom: That's fucking class that g, everybody is gonna be well jealous init
Dave: That fartcan sounds shite
A number associated with the richness of flatulence. A number 2 rating is average and might be mistaken for "forgetting to take the garbage out" A number 4 rating will typically clear out a medium sized room while a number 8 is a serious combustion and explosion hazard.
Arthur, at any party could always be counted on to rip one with a number 4 fartane rating. People who knew him well would always reply with a blessed be the fruit right before they made their exit.
Oversize "performance" exhaust found on underpowered import "rice" cars. Generally reduces performance and makes the car sound like it's farting, or like a lawnmower.