A C414A ON FINAL APCH HAS LOSS OF ENG PWR AND LANDS OFF THE RWY TO CLR LOC ANTENNA. CAUSE OF LOSS OF PWR UNKNOWN.

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EXPEDITING APCH. MAINTAINED HIGHER THAN USUAL APCH SPD. PWR WAS REDUCED SMOOTHLY BUT MORE AGGRESSIVE THAN BEFORE FROM APPROX 30 INCHES MANIFOLD PRESSURE TO 15 INCHES MANIFOLD PRESSURE (LIQUID COOLED ENGS -- RAM SERIES V). IN RAPID SEQUENCE AS INDICATED AIRSPD REACHED APCH FLAP AND GEAR SPDS THEY WERE DEPLOYED. WHILE VISUAL GLIDE PATH WAS MAINTAINED THE AIRSPD DECREASED AND I WANTED ADDITIONAL PWR TO STABILIZE AIRSPD BEFORE ADDING THE REMAINDER OF FLAPS. PWR DID NOT INCREASE WITH INCREASED MIXTURE; PROPS AT CRUISE RPM AND ADDITIONAL THROTTLE (MANIFOLD PRESSURE). THE ENGS WERE RUNNING SMOOTHLY; IT FELT AS IF THEY WERE STILL PRODUCING SOME PWR; BUT INSUFFICIENT TO CLR THE LOC ANTENNAS. I NOTIFIED THE TWR OF PWR PROB AND INTENDED LNDG OFF RWY TO L (CLR AREA). I WAS MAKING A MORE AGGRESSIVE PWR REDUCTION THAN IN THE PAST. THAT IS SUPPOSED TO BE AN ADVANTAGE OF LIQUID COOLING; IE; NO SHOCK COOLING. THE PROB WAS DISCOVERED AFTER XING THE PERIMETER FENCE AND ACCESS ROAD AROUND THE RWY. THE AIRSPD WAS DECREASING AS PLANNED; BUT WHEN I WANTED ADDITIONAL PWR TO STABILIZE AIRSPD IT WAS INSUFFICIENT. THE RWY IS SLIGHTLY ELEVATED AND THE LOC ANTENNAS WERE RISING IN MY FIELD OF VIEW DESPITE MAINTAINING BEST GLIDE SPD. PERCEPTIONS; JUDGEMENTS; DECISION: JUDGEMENTS REGARDING ACFT HANDLING SEEMED STRAIGHT FORWARD. I HAVE LATER THOUGHT ABOUT TRYING TO FEATHER THE PROPS; BUT AT THE TIME I FELT THERE WAS STILL THRUST. I DID NOT TRY TO INCREASE RPM FROM THE 2300 RPM INDICATED AS THAT MIGHT HAVE ADDED MORE DRAG. THE DECISION TO EXPEDITE THE APCH WAS IN RETROSPECT OVERLY AGGRESSIVE ON MY PART. AFTER LNDG AND DURING THE LNDG ROLL; PWR SEEMED TO RETURN AND THE THROTTLES BECAME RESPONSIVE. I NOTIFIED TWR AND RECEIVED CLRNC TO TAXI TO PARKING. SHUTDOWN INSPECTION WITH COWL REMOVAL DID NOT REVEAL ANY LINKAGE PROBS. THERE WERE NO LEAKS NOTED. THERE WERE NO ODORS OF FUEL; OIL; HYD FLUID; OR ANTIFREEZE (COOLANT); AS VIEWED BY MYSELF AND A&P. THOROUGH RUN-UP SEVERAL HRS LATER DID NOT PRESENT ANY IRREGULARITIES. ONCE BACK AT HOME BASE; AFTER AN UNEVENTFUL RETURN FLT; THE NEXT MORNING (MONDAY) MY MECH CALLED ENG MANUFACTURER FOR QUESTIONS AND TROUBLESHOOTING. HE SPOKE WITH THE ENGINEERING THAT DID THE TESTING OF LIQUID COOLED ENGS; AND HE DIDN'T HAVE ANY SPECIFIC IDEAS. HOWEVER; HE WANTED TO TALK TO THE FIELD REPRESENTATIVE FOR ANY POSSIBLE ADDITIONAL INFO. WE HAVE NOT HEARD ANYTHING FURTHER; SO I'M LEFT WITH THE FIRST CONCLUSION THAT: THIS RECENTLY FOLLOWED A 100 HR INSPECTION AND TUNE-UP. BEGINNING COLD WX THE MIXTURES WERE SET RICHER THAN IN SUMMER; DURING USUAL ANNUAL. THE RAPID THROTTLE REDUCTION MAY HAVE CREATED AN OVER-RICH MIXTURE AND SUBSEQUENT PWR REDUCTION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE AIRPLANE IS PWRED WITH 2 IO-550 LIQUID COOLED ENGS. THE RPTR SAID ON FINAL APCH THE THROTTLES WERE RETARDED QUICKLY AND THE MANIFOLD PRESSURE DROPPED FROM 30 INCHES TO 15 INCHES. THE RPTR STATED WHEN ADVANCING THE THROTTLES; THE ENGS DID NOT RESPOND BUT REMAINED AT 15 INCHES MANIFOLD PRESSURE. THE RPTR STATED WITH NO PWR TO INCREASE AIRSPD AND CLR THE LOC ANTENNA; A DECISION WAS MADE TO LAND OFF THE RWY IN A CLR AREA TO THE L. THE RPTR SAID THE LNDG WAS MADE WITH NO DAMAGE TO THE AIRPLANE OR ARPT FACILITIES. THE RPTR STATED ON TAXI ONTO THE RWY; PWR WAS RESTORED AND WHEN THE ENG WAS INSPECTED; NOTHING WAS FOUND TO CAUSE THE LACK OF PWR. THE RPTR SAID THE MANUFACTURER WAS CONSULTED AND HAD NO INFO OR RPTS OF ANY LOSS OF PWR WITH RAPID THROTTLE MOVEMENT. THE RPTR STATED THE MIXTURE HAD BEEN ADJUSTED TO THE RICH SIDE AT THE LAST ANNUAL INSPECTION AND MAY HAVE CREATED AN OVER-RICH MIXTURE CAUSING THE PWR REDUCTION.