there is no more or less power made by the fuel. this has been known for a long time to drag racers. 9.5:1 compression is what decides the octane, it is the detonation that is controlled. there is no more thermal expansion between regular vs premium. the difference in power is due to the detonation (ping/Knock) from the regular octane. if you have detonation you are not using the full potential made by the combustion process. higher octane stops this so you see more power due to proper burn. higher compression gives higher power output but requires the higher octane to control ping. thats why a 350 small block chevy can make 500+ HP with 13:1 compression but must run 108 octane to stay alive. knock/ping with hammer your engine to death, burn holes in pistons and so on. if you have to use regular, drive easy to reduce the chances of detonation. your chances of detonation go up with higher loads applied (more throttle) when passing, racing or driving up inclines. i had to use regular on our way to Sturgis this year and it was fine, just drove easy. dont recommend it for daily driving though, just emergencies. it's better than pushing.