There are no mechanical changes to the engine when installing a Compressed Natural Gas conversion.
The gas is stored at 220 bar in gas cylinders typically located in the boot of a sedan, in the load bed of a pick-up/bakkie or attached to the chassis of small to medium sized trucks such as the NPR 400.
The gas is piped from the cylinder to the reducer/regulator, which reduces the pressure from 220 bar to 1.2 bar typically or as required by the particular engine. From the regulator the gas is piped to an injector rail and just like a Petrol injector rail, the gas is injected directly into the inlet manifold.