The first prototype built by Hydrofuel Inc was the conversion of a 5.0L 1981 Chevrolet Impala to monofuel NH3 operation.  It was to demonstrate the feasibility of running a conventional automotive engine on NH3.

There were many challenges to overcome with this prototype.  Besides designing and sourcing the NH3-compatible fuel system, a major challenge was to invent an ignition system for the mono-fuel NH3 system.  The design team also evaluated the feasibility of converting diesel engines to NH3-fuelled spark-ignition at this time. A diesel pick-up truck was converted to NH3 monofuel spark-ignition operation but was not road tested.