The change in exhaust system of a automobile is illegal as it alters the exhaust note as well as the emission standards of the machine. You must have seen the free flow exhaust on the track based Gixxer MotoGP edition. That exhaust is illegal for the roads but can be used while the bike is on the track. You should not change the same as Gixxer series comes with a very beautiful chrome lined exhaust, one of the best looking below INR 1,00,000. The bike's 154.9 cc engine produces 14.6 BHP and 14 NM of torque, with a mileage figure of 40-45 kmpl. The change in exhaust would cause all the figures to change, specially the mileage drop. Gixxer series starts at a price of INR 75,000.