hmm haroon u have save the money which is approximately 18 K just keep your mehran well maintained i m telling you some basic maintainence which you should not compromise on ...
get your mehran tuned and tappets adjusted
keep your air filter clean after every 2 week go to car wash shop take out the air filter and say them to put pressurized air in it as on cng the air filter get dirty very early results in decrease in acceleration and blockage of air cause damage of seetings of the tuned car...
put ngk platinum spark plugs and rspec 10 mm spark plugs wires... and you feel some more power in pick up and increase in mileage..