What Do Valve Jobs do?
Valve jobs have a few duties to perform. First of all, they seal combustion gases in the cylinder and stop them from leaking back into the ports, costing you valuable horsepower. Second, they transfer heat, specifically on the exhaust side of the head where valve head temps can excees 1300 deg F. If you have too narrow a contact patch between the seat and the exhaust valve, you will likely "burn" it, which is a generic term for pieces that will probably chip and fall off into the cylinder. Again, not a good scenario. Third of all, they help guide air around the valve and into the cylinder. Remember, the valve is THEE major restriction in the port, as its sitting right smack dab in the middle of the flow path. The incoming air thats rushing through the port WANTS to flow through the center of the valve head. Of course, this is impossible, so it does the only thing it can do, divert itself around the valve and into the cylinder. As its diverting itself around the valve , the importance of the shape of the valve seat comes into the play. When I reference the shape, I am referencing angles, radii, and their respective widths. With the proper shape valve seat you can effectively guide that incoming stream of air into the cylinder smoothly and without creating turbulance behind the valve, which is one of the negatives of a stock/bad valve job.
What is the differnece between a "Race" valve job and a "Street" valve job?
Good question. As the valves operate in the head, they slam up and down onto the seats hundreds of thousands of times. The contact patch between the valve and the seat becomes larger and larger as time goes on. The wider the contact patch becomes, the less effectively the air can turn into the cylinder, costing torque and horsepower. If long term durability is of no concern, and the cylinder head will be used for race purposes only, we may opt to use a thinner seat, which will flow more air and make more power. It WILL pound out faster than a street valve job, which will use a thicker seat and stand up to many thousands of miles as a street car. The heavy duty valve springs often used in race heads compound this problem even further, as they slam the valve back on to the seat with more force every cycle. This is the major difference between a "Race" valve job and a "Street" valve job.
What is the right package for me?
First off and most importantly , you have to be honest with yourself, and your head porter. Telling him it is a race only engine that will never see the street, and then it winds up taking 100 mile road trips, is not the smart thing to do. When you told him it was race only, he probably put a race valve job on it, and now that you have put some miles on it, it is worn out and leaking. Is this the head porters fault or some sort of shoddy work? NO! This is the customers fault for not being honest with his intentions for the car. Dont get caught up thinking that just because you tell the porter that it will see street useage that he wont give it his all. You will only be setting yourself up for dissapointment later.