Glasair Sportsman – Emergency Landing in Field

N991BW, a privately operated amateur built Glasair Sportsman 2+2 aircraft, was conducting a local flight from Langley, BC (CYNJ). While in the Glen Valley training area the pilot observed an unusual noise coming from the engine (Aerosport IO375). The pilot elected to return to CYNJ. During the approach to CYNJ the pilot requested priority from ATC for landing on runway 25. Shortly after priority was given the aircraft experienced a reduction in power. The pilot made an emergency landing in a rhubarb field approximately 3.5 nm NE of CYNJ. Just after initial touch down the aircraft nosed over in the soft field. The aircraft came to rest inverted. The pilot and passenger received minor injuries, the aircraft was substantially damaged.