Suzuki Other Engine Poor Mileage

I Want To Upgrade The Exhaust From Stock, To Get A Louder Sound From The Car. Would There Be Nay Effect On Fuel Consumption Or Performance...

I Have The Maruti 800 Lpg Model. Carburetor Type. I Am Using Lo Gas Lpg Kit. My Friends Are Getting Around 350 Km Mileage For 14 Kg Gas. But...