first off......how does a Cessna310 burn 15-20GPH????? not sure which model you own but the first and lowest engine model has 2 IO470's 240 HP.. A piper twin comanche probably the best twin time builder has 2 C172 engines, IO320's 160HP and burns around 16-18GPH total. maybe 15-20 GPH per side out of that thing. the one C310 i flew in burned 32GPH at 75% power. now Im sure we're gonna be cruising at 55% power but what could that possibly put us at 25-28GPH and thats if you have the early model 310?