The pilot reported that while in the airport traffic pattern, the airplane's engine lost power just after completing a turn from the crosswind leg to the downwind leg of the pattern. At the time of the engine failure the airplane was about 1,100 feet above mean sea level (approximately 630 feet above ground level). The pilot reported that the airplane abruptly pitched up and he attempted one restart to no avail. He reported that the airplane continued to decelerate with full forward stick pressure. In order to keep the airplane from stalling the pilot rolled the airplane inverted and pulled back on the stick to lower the nose of the airplane. He then rolled the airplane back upright and pulled back to arrest the descent before contacting trees. The pilot reported that the homebuilt airplane is an all aluminum version of the Vari-Viggen design and believed that the pitch up following the loss of power was due to the high thrust line location of the pusher engine configuration. The airplane was powered by a converted Mazda rotary automobile engine. An examination of the engine and fuel system revealed sufficient fuel and fuel within the fuel line to the carburetor. A visual examination of the engine revealed no anomalies.