The purpose of the flight was to break in the engine and to evaluate the systems and flight characteristics of the newly-built RV-8A.
During the flight, the private pilot observed an elevated cylinder head temperature, which he controlled with airspeed, altitude, fuel mixture and engine power settings.
He returned to the airport in Salem, Oregon, and, in the traffic pattern, the engine began to run rough, followed by a total loss of power.
The pilot subsequently landed in an open field about 150 feet short of the runway threshold.
A post-accident examination of the fuel system and a test run of the engine revealed no mechanical anomalies that would have precluded normal operation.
The reason for the reported loss of engine power was not determined.
Probable cause: A total loss of engine power for undetermined reasons.
NTSB Identification: WPR16LA049
This January 2016 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

The engine is an IO375, with dual P-mags, that test ran ok.
With new, hot running cylinders and having to fly an extended downwind, the only thing I can suspect is vapor lock… ?
Perhaps Carb ice? Regardless, engine failure and the immedate emergency landing afterwards something that remains a real possibility for pilots of SE aircraft. Managing an engine failure is one of those essential skills we should practice frequently. That, and continuous awareness of survivable landing sites are critical when “it” happens.