First of all, let me clear one confusions.
LIANA AND SWIFT HAVE THE SAME ENGINE!!!
Next, factory fitted CNG in Liana is a pleasure to have. It will rev smoothly to redline and will give you excellent average.
I got 200 Km's on a single tank on Motorway last weekend. Got CNG from Kot Momin and drove into Islamabad... 205 Km's on the odo!
First cylinder gave me 180 Km's. I basically went to Islamabad in 2 cylinders (drove on petrol for about 10 Km's in between.
What else do you need? Alhamdollillah.