Mine is doing 9~10 kpl in city at the moment, and the EFI wiring is still not fiexed, and O2 sensor not checked. Once i sort out these, it is expected to give 12kpl at least.
For me:
CNG per KM = 75/16 = Rs. 4.7
Petrol per KM = 108/12 = Rs. 9
Additional on petrol = (9-4.7)*500Km = Rs. 2100
This additional Rs. 2100 is in the ideal case that the car runs solely on CNG, which isn't the case at all. Actual impact is only Rs. 1200~1500
Now what will it save:
1. Min 4 trips to CNG station (12Km round trip each)
2. 8 hours passed in CNG line on those trips
3. Mental tension
4. CNG maintenance
5. Boot space (Though my Nissan still has plenty of boot space)
6. Engine early death