these days you are better off buying a larger engine if you want more power than trying to port an engine,35 years ago porting could make a big difference on the loop scavanged designs that were being made but with schnurle porting designs,the most power and reliable idle porting is usually built into the engine usually if you are porting the exhust port as described above more power will be seen with a pipe than with a muffler,crankshaft timing also plays a part in the power equation but again better to buy a larger engine.as clearence lee said nothing in the power department takes the place of cubic inches.you also may want to try different props as they can make a difference in speed also.