When I retired about 7 years ago, the buzz word was "tumble". A lot of CFD work on computers to design a port where the air literally "tumbled" down the port, and into the cylinder. It is all about breaking the fuel molecules down as small as possible so when the chemical reaction is initiated, the combustion is complete, and what doesn't burn is handled by the catalyst. Let me say , I've seen the time from open chambers, to air injection 2 cycle, to tumble ports, with the end game being to "of course" (eliminate pollution) improve efficiency.