What is the average cost of switching from petrol to petrol plus methane?

The cost may vary for several reasons.
It is important to distinguish between conversions of non-catalytic and catalytic cars. Geographical area, tank capacity and the number of cylinders are also important factors.
With catalytic cars the price may vary depending on whether the engine has fuel injection or not.
For example, in Northern Italy the conversion cost based on a 90-litre cylinder, excluding road tests, is in the region of:

• €1500 for a catalytic car without fuel injection;
• €1950-2050 for a car with fuel injection.