Just recently I drove a Passo (Specs are, 1000 CC (precisely 996 CC), 3 cylinder 12 value, DOHC (double overhead camshafts, twin cam), Model DBA-KGC35-AHEDK, 1KR FE Engine, Hanna Plus, 165 / 70 R14 Tyres, start slot, CVT, ABS, 2 x air bags). I did not change any thing in the car no plug, starter, battery, coolent, any thing and decided to drove it in city (DHA Islamabad to F-11, my usuall ride) and on motor ways from Islamabad to Peshawar and Islamabad to Hassanabdal and to Abbottabad and back off course.
I used 26 psi on front tyres and 30 in the rare one. Used PSO Premier XL petrol for my rides. I am kinda take care driver, where I do not push too much on accelerator, My maximum speed usually remain with in road priscribed limits.
My experience shows following results with above vehicle.
In city with AC = 14 Km/L
In city with out AC = 16.3 Km/L
On Highway with AC = 16 Km/L
On Highway with out AC 19 Km/L.
These are the averages and over all readings I calculated to the best of my knowledge, Odometer at times were showing 21 Km/L as well.
Ride was comfortable, other than Body kits on Hasanabdal to Haripur were kissing on bumps.
other than the above calculated superb millage, I wont consider installing CNG on Passo for below reasons as well.
CNG time is over, LPG is around corner.
Risk Involved with safety
Reduction of boot space in vehicle.
I hope this clarifies.