Thank you so much for your advices.Now le me give you an advice :D
I went to montgomery road yesterday and just inserted iradium plugs of NGK for Rs.2500/- (4 plugs set) and my car performance has been increased about %30.
Acceleration is so good now that car on CNG in 2nd gear the tires slip out on the road with the speed
About air intake lots of peaplle told me that it will not work on CNG.
Now just the second thing i am going to do will add muffler and it will also increase the acceleration of the car upto 20%