@jules, i think it is really cool that you have 4 banger converted to CNG. is the conversion totally controlled by the guvment in italy like it is here? we cannot buy the conversion kits in the US, and are subject to impound if the feds find an unauthorized conversion. but the cost is really steep if you go to the conversion shops here, not as cheap as there. of course it is even cheaper in argentina or pakistan or iran where the use of CNG has made the most inroads already.
was the 4 cylinder fuel injected and did you retain the ability to use petrol? the honda civic can get about 40 mpgge from what i have seen the guys over here brag about, so since natural gas in the US is selling for about $3.80/mmbtu here, and gasoline is about 100k btu/gallon, that is about 38 cents/gallon equivalent for CNG before compression costs. one cent /mile.
in the US we have extensive high pressure pipeline systems all over the country where the natural gas is already pressurized to 3k psi or more so the filling stations could be located along the major pipeline routes and tapped at high pressure so filling can be rapid, and not pumped up from the low pressure domestic mains. so that would be about 9 cents/liter equivalent, or .12 euro/liter. how much do you pay for CNG?