What is the purpose and benefits of say a 5 angle plug job? I understand it somewhat in moving the spark plug to a more favorable location.. does anyone care to elaborate on this? I'd like to know.. thanks
Moving the plug to a more central location in the combustion chamber is a common practice in high end aftermarket cylinderheads heads. But this has nothing to do with the valve job.
The 3 angle (most common performance aplications) vlave job, refers to the 3 angles on the edge of each valve seat. (The hard ring in the head that the back side of the valve rests against, while closed, to seal the chamber from the port) By putting 3 angles or 5 (in high end or racing aplications) it smoothes out the corner that the air has to flow around, to get in and out of the chamber. (out of the intake port, into the chamber, then out of the chamber, into the exhaust port)
Just as water likes a smoothe corner to flow around, so does air (their flow characteristics have many similarities). If there were just two angles (old, OLD school stock head technology) the air would "tumble" as it tried to "flow" around the corner, and this would slow it down... slow air is bad air. You want high velocity to get high quantity in a short period of time. That is why (one reason) modern heads have smaller volume, better shaped ports that can flow MORE air, than the old school cavernous ports of a 351C4v or a 427tunnelport that didnt flow good at low valve lift. (but flowed like Hoover Dam at .600)