The whole idea behind porting is to round any sharp edges on the sleeve ports. Rounding sharp edges will allow fuel and air to move into the combustion chamber more effeciently. consequently porting the exhust port will allow the spent gasses to leave the combustion chamber more effeciently also. It must be done very carefully so as not to remove to much metal. If to much is removed it will screw up the sleeve and if a rough spot is left it will cause a scuff or a scratch on the piston causeing a loss of compression. I hope this will set ya all straight . Good luck