First of all I apologise for the dual post of the same topic. It was error as my connection in between.
AkbarGr8: It is with AC in current Karachi city driving (lots of construction and blocks). Cannot drive without as in city heat. Moreover it is standard CITY, no rims or anything else. No modifications.
Cylestyne: I will be bankrupt till 10,000km 
I am not a active driver like you guys here. I drive my car in very passive mood, no gr8 pickups required for me no racing. How much will I loose if I install CNG keeping in view that I dont mind my car being slow after signal stop when the light turns green.
Thanks