As the pilot rotated the aircraft for takeoff he heard several bangs and felt there was an accompanying power loss, so he aborted the take-off. When it appeared he would be unable to stop in the strip remaining he deliberately ground looped the aircraft. The nosewheel leg was damaged and the propeller struck the surface of the strip, necessitating an engine strip - the propeller was not damaged. An inspection of the aircraft did not find any fault with either the engine or the braking system. The blacksoil strip was found to be very soft and it is considered that the retarding action of the strip caused the pilot to believe a power loss had occurred. The bangs heard by him were probably caused by clods of dirt hitting the fuselage.