Knocking basically depends on the amount of octane in petrol, the lower the worst.
Even Alto does knocking on petrol (if the race is low) and on CNG it doesn't do that.
I have City 09. I was wondering what happens to the 'Real time consumption meter' when you're running it on CNG?
My car gives me 21 Km/l if I have to travel 100 kilometers (mostly from Rawalpindi to Peshawar) which is about the same as CNG. CNG would cost about 500 rupees of CNG from Peshawar to Rawalpindi, and I filled up my tank in Peshawar and refilled it in Pindi and it very difficultly got 600 rupees of fuel in it. (Difference of 100 rupees).
But may be there is something I do not know? Yes, local par its really very bad.. that is unquestionable. But if you have to drive 100 kilometers everyday.. it shouldn't be that much of a problem..
Plus CNG kit is also not free. It must have cost you about 40,000 rupees, right?
What does the consumption meter show when you're running on CNG?