Go for best available CNG kits, you get the performance loose nearly 35%...means when you will drive CNG you will find weak as on Petrol you get real boost....But its not that mush depressing........but if you never drove a CNG car you may need some time to adjust your mind. Otherwise no tension with engine or other stuff. You can go for CNG to save the bucks if you ever need a real Vitz power simply switch on to Patrol and cheers!