Hypothetically, if you insulate an engine block, and force the heat back down, would it run more efficiently?

Hypothetically, if you insulate an engine block with reinforced carbon-carbon, or silica ceramics, and it forces the heat back down into the cylinders, pistons, and gas, would the engine run more efficiently, since less gas would be needed to ignite the combustion, because the temperature in the chamber would already be elevated?