most places will tell not to use them becausethe cost of paying someone to port them and machine work.but if you take out cost factor it changes the whole idea.my whole thing with aftermarket heads vs ported factory heads is if i can make the stock shit reach my horsepower goal why buy aftermarket heads.and also why buy a small ass aftemarket heads (CC runners) for a small 302 street motor.now if you wanted to build a high rev bigger cubic inch motor the you will need some big CC runner heads that will perform much better then ported tock heads.YOU HAVE TO HAVE A GAME PLAN BEFORE JUST THROW PARTS AT A MOTOR.YOU CAN"T JUST THROW ANY OLD HEADS,CAMS,AND ETC.YOU WANT A WELL MATCHED APPLACTION FOR WHAT YOU PLAN ON USING THE CAR FOR.