Not an expert, but will try to answer some of your queries. Q: Does a crack/leakage in the exhaust system affect the efficiency so much?? I can understand it will ,but this much ??? A: I know that it does reduce FE, though no idea by how much. I would suggest you get it repaired instead of bothering about exactly how much FE gets reduced. Q : What is the correct way of repairing such a leak? A patch welding was something the service centre guy was referring to. A : Used to have this problem with our old M800 when it was used in Kerala - usually the muffler would develop holes due to rust or the place where the end pipe joins the muffler. I would get under the car, unbolt the assembly, take it to the nearby welder and get it rectified. All for 50 bucks or so, while a new muffler assembly cost around 15-20 times that much. Q : giving for repair does the full exhaust from the header to the end can require to be removed or only the connecting pipe can be partially disconnected. A : The whole exhaust system is made up of 2 or 3 removable parts. For the M800, I think it was 2 parts. So, remove only the part where you have the crack. Not sure how it is for the Lancer. Q : If the crack is left unattended to (remote possibility though) just because I love the sound what future damages/disadvantages can I anticipate. A : Pick up also gets affected. Though I have to admit I used to love the sound it made when there is a crack in the muffler.
P.S. : I love the FFE sound, but hate tampering with my car to get the mod done. Especially having to throw out the catcon. Sometimes I think it would be nice to make a small pin hole in the muffler, just for the sound.  |