Gas porting allows combustion gasses behind the top ring, actually pushing the ring out against the cylinder wall during the power stroke for a better seal. This action allows the use of a thinner ring, which during the remaining engine cycle has less friction than a thicker ring. Gas porting does cause increased ring wear, thus is generally considered only for competition. Either vertical gas porting such as seen here, or horizontal gas porting (as seen in our previous photo caption) via holes at the top of the top ring groove, can be used depending on application. JE's Randy Gillis explained that vertical porting can be compromised by carbon buildup on the piston top, so are typically used in short burst applications like drag racing and tractor pulls.