Frequently Asked Questions
Q: Why aren’t the intake ports on your head
polished?
A: Intake ports are not polished. This is because we do not want the boundary layer of air (small layer of air on port walls that has very little velocity relative to the middle of the port) to be laminar flow. Laminar flow creates a larger boundary layer of air (relative to a turbulent boundary layer), which effectively chokes the port. With a turbulent boundary layer more of the port is flowing at high velocity, there is less chance of fuel puddling on the walls, and you get better fuel atomization. This isn’t just theory, it’s been proven to work by many winning racing teams.
Q: OEM or bronze valve guides?
A: There is a lot of misconception and misinformation about bronze guides out there. In our experience they work ok, but halve a shorter lifespan than factory guides. The bronze is softer than your valves and they will wear out and cause excessive oil consumption. The factory guides work well for 150k and do not wear the valve stems. Some vendors will try to convince you that you need the softer bronze to not wear the valve stem. That is BS, valve stem seals are actually a very slow, very small, controlled oil leak. They allow just enough oil to get to the valve stem and provide lubrication. There is no need for a softer guide. In the end the choice is up to you, but my car has OEM guides.
Q: Should I run oversized valves?
A: It depends on what you are looking for. On the flow bench 1mm over valves perform great, in terms of real world performance and bang for the buck they aren’t a clear winner. The problem with larger valves is that the stock valves are already shrouded at the edge of combustion chamber and with a 86mm bore very little material can be removed; note that with a 2.4L you have more material that can be removed. What this means is that when the head is installed on a block 1/8 to a ¼ of the valve is blocked for airflow. They do have the advantage of allowing you to enlarge the valve throat and get a better bowl shape though. Supertech valves are also swirl polished (reducing the boundary layer on the valve) and back cut which can help flow on the intake side significantly. In testing we have seen a 15hp gain with 1mm valves on cars in the low 400hp range. Whether a 4% hp gain is worth $325 is up to you.
On the other hand .5mm oversize valves are highly recomened, their diameter increase does not increase valve shrouding, and the larger diameter means the valve won't sit as deep in the seat. A valve that is high in the seat will flow significantly more than a valve that is sunken into the seat.
Q: What are the Supertech valve spring rates?
A: The single springs have a 78lb seat pressure (39.6mm) and 200lb open pressure (28mm). The dual springs have a 100lb seat pressure and 250lb open pressure.
A: Intake ports are not polished. This is because we do not want the boundary layer of air (small layer of air on port walls that has very little velocity relative to the middle of the port) to be laminar flow. Laminar flow creates a larger boundary layer of air (relative to a turbulent boundary layer), which effectively chokes the port. With a turbulent boundary layer more of the port is flowing at high velocity, there is less chance of fuel puddling on the walls, and you get better fuel atomization. This isn’t just theory, it’s been proven to work by many winning racing teams.
Q: OEM or bronze valve guides?
A: There is a lot of misconception and misinformation about bronze guides out there. In our experience they work ok, but halve a shorter lifespan than factory guides. The bronze is softer than your valves and they will wear out and cause excessive oil consumption. The factory guides work well for 150k and do not wear the valve stems. Some vendors will try to convince you that you need the softer bronze to not wear the valve stem. That is BS, valve stem seals are actually a very slow, very small, controlled oil leak. They allow just enough oil to get to the valve stem and provide lubrication. There is no need for a softer guide. In the end the choice is up to you, but my car has OEM guides.
Q: Should I run oversized valves?
A: It depends on what you are looking for. On the flow bench 1mm over valves perform great, in terms of real world performance and bang for the buck they aren’t a clear winner. The problem with larger valves is that the stock valves are already shrouded at the edge of combustion chamber and with a 86mm bore very little material can be removed; note that with a 2.4L you have more material that can be removed. What this means is that when the head is installed on a block 1/8 to a ¼ of the valve is blocked for airflow. They do have the advantage of allowing you to enlarge the valve throat and get a better bowl shape though. Supertech valves are also swirl polished (reducing the boundary layer on the valve) and back cut which can help flow on the intake side significantly. In testing we have seen a 15hp gain with 1mm valves on cars in the low 400hp range. Whether a 4% hp gain is worth $325 is up to you.
On the other hand .5mm oversize valves are highly recomened, their diameter increase does not increase valve shrouding, and the larger diameter means the valve won't sit as deep in the seat. A valve that is high in the seat will flow significantly more than a valve that is sunken into the seat.
Q: What are the Supertech valve spring rates?
A: The single springs have a 78lb seat pressure (39.6mm) and 200lb open pressure (28mm). The dual springs have a 100lb seat pressure and 250lb open pressure.
