Recent legislation, including the California Clean Air Act of 1988 and the Federal Clean Air Act Amendment of 1990, includes off-road engines, equipment, and vehicles as targets for new exhaust emissions regulations. The Santa Barbara County Air Pollution Control District in cooperation with EXXON USA is conducting a major Low NOx Demonstration Program including mobile sources, construction equipment, and offshore equipment. As a part of this program, an existing backhoe has been retrofitted with a low NOx engine and demonstrated in the field.This paper discusses the work performed to allow Case model 580 backhoes to be retrofitted with Cummins 4BTAA3.9 on-highway turbocharged diesel engines. A standard production conversion kit can be used to mount the new engines in place of the older existing JI Case engines in some models while other newer models already have 4B3.9 engines. In addition, an air-to-air aftercooler and associated plumbing was designed and installed. The air handling and exhaust systems were redesigned for the turbocharger.The engine was emissions tested following the California 8-mode test cycle in two configurations. The first test was with the engine in its automotive configuration with a rating of 62 kW at 2500 rpm. The second test was in the backhoe configuration with a rating of 51 kW at 2100 rpm. NOx emissions were higher with the lower speed and power rating.