On January 15, 1993, at 1639 central standard time, a Pitts S1C, N22R, was substantially damaged when it impacted the ground near Godley, Texas. The private pilot (owner) sustained minor injuries. Weather for the 14 CFR Part 91 flight was visual meteorological conditions. During an interview with the pilot conducted by the investigator in charge and in a written statement, the pilot reported the information in this paragraph. He departed a local private grass strip to practice aerobatic maneuvers. "Prior to entering the designated aerobatic block the pilot decided to perform some flight maneuvers, so as to warm up the airplane." During the warmup maneuvers he stated that the "engine began to cough." He cycled the throttle lever in an attempt to clear the engine and applied carburetor heat. He further reported that the engine never lost complete power. The pilot selected what he thought was a suitable area to land and executed a forced landing. An inspection of the accident site revealed that the airplane impacted the ground on terrain that was sloping downward and away from the direction of the approach. Physical evidence at the scene revealed that the airplane left impressions of the tail landing gear, main landing gear, and propeller at the initial ground contact (144 feet prior to it's final resting place). The ground signatures were measured and they matched the dimensions of the distance from the tail landing gear to the main landing gear and from the main landing gear to the propeller of a normally configured airplane. The main landing gear collapsed and the propeller mounting flange was sheared opposite the direction of rotation. Examination of the airplane revealed that the engine did not have a data plate installed and the owner stated it was not present when he purchased the airplane. The normal engine configuration for this airplane is a 140 horsepower, this airplane had a 180 horsepower engine installed. The propeller had separated from the mounting flange and each blade exhibited equal distortion. An examination of the propeller mounting flange revealed that it had sheared opposite the direction of rotation. Soil and grass were embedded in the remaining flange in a twisting motion. The propeller assembly was located 44 feet from the initial ground contact. Five propeller strike marks were found four feet in front of the initial ground contact. Physical evidence indicated that the airplane cartwheeled one time prior to reaching it's final resting place. There was a large quantity of fuel present at impact (amount undetermined due to spillage). A witness at the scene reported that the airplane performed low level aerobatic maneuvers over his house and another adjoining house. The same witness saw the airplane impact the ground. A review of the icing probability charts indicated that the airplane was operating in an area conducive to serious icing in pressure type carburetors.