In this paper we describe the experimental apparatus used to validate concepts associated with a bimodal internal combustion engine for use in natural gas vehicles (NGV's). In one mode, all engine cylinders fire normally providing locomotion for the NGV. In the other mode, one cylinder of the engine is used to compress residential natural gas, in multiple stages, to a standard US compressed natural gas (CNG) vehicle storage tank pressure of 250 bar. In the refueling mode, while the single cylinder is compressing natural gas it is powered by natural gas combustion in the remaining engine cylinders. Here we describe the engine dynamometer testing used to validate the bimodal engine design described in a companion paper. More specifically, a base compression ignition engine is powered by an AC motor while pumping air into storage tanks while all relevant thermodynamic parameters are recorded. The experimental data is compared with numerical model data in anticipation of convergence between the two. The air compression tests are completed en route to completing the same tests with natural gas.