Aluminum 5-port Unleaded Cylinder Head, Standard

Everybody has their own opinion on this subject. The most experienced people will tell you that the best way to maintain your engine performance is to accept the fact that valve jobs need to be done 2 or 3 times more often than rings and bearings! And this data base was concluded when leaded gas was the norm! Now that unleaded is all you can get, valve jobs are needed even more often! The purpose of a valve job is two fold; first the valve seats. The impurities in the air and gas often get trapped between the valve and the seat in the head; under worst conditions stopping the valve from closing, but more commonly being smashed enough to allow just a little seepage of hot gases.