LOL I must have. Sorry now the edit time as expired so here is the remaing part:
How do you PnP heads?
This is a common misunderstanding, most people think that gasket matching the intake and exhaust ports then polishing the runners to a mirror finish is the way to PnPheads, this is incorrect. While some gains may be achieved in some instances, heads usually suffer from this process especially matching the exhaust ports where testing has indicated that too large an exhaust port can cause the heads to have very poor performance.
Port work is a process where the intake and exhaust ports are worked to the desired I/E ratio that fits the application (ie larger exhaust ports for turbocharged vehicles, smaller for N/A, etc). â??Polishingâ? is also a relative term that doesnâ??t mean you want a mirror finish on the intake runners, you actually want little dimples along the runner that create eddies or pockets of air that reduce the friction losses as the air enters the combustion chamber.
This process of PnPheads is best described by cutting the radius bend a little then â??feelingâ?? with your fingers, flow the heads on the flow bench, then repeat until you reach the desired angle you need depending on the application. In naturally aspirated cars you want the shape of the port to actually aid in â??suckingâ?? air in, in forced induction applications you want to maximize flow, however this shape is different between Turbocharged and Supercharged; specifically around the exhaust ports.
The combustion chamber is another area of tedious concern. When installing larger valves, larger seats must be installed as well. When installing larger valves and seat it causes massive disruption in the combustion process unless the area around the valves are properly cut down (commonly knows as unshrouding the valves) to again meet the specifications of your application (N/A, Turbo, SC, etc). There is a right way and wrong way to do this as well. The wrong way is taking out, as much material as you think doesnâ??t need to be there. The right way is taking away only what doesnâ??t need to be there to allow proper flow around the valves but doesnâ??t negatively impact the quench area and flame propagation of the combustion process. You must use a flow bench to discern if your cutting is helping or hurting.
Mult-angle valve jobs are also usually performed when PnPâ??ing heads. This allows the entrance of the valves to be more rounded (ie. flow better) while still able to seal better then cheaper factory valves and seats. Refer to a how-it-works web site for pictures of this process.
Decking the heads is another process that is of concern. This consists of a planeing process to remove any imperfections in the surface of the heads that mate to the block or to repair a warped head. With Duratec specific engines the piston to valve clearance is VERY small, removing to much material from the surface of the heads could allow the piston to actually hit the valves resulting in total engine failure.
