Project Toyota Supra MKIV, Part 3: The Cylinder Head


With the gasket out, now it's just a matter of grinding up to the lines with a port grinder. 


Perhaps you noticed the sharp, knife-edged port dividers. These are not good because they not only reduce flow (which is probably a little counter-intuitive), but also promote cracking in that area.  


FRP's Jeff Gerner at work with his port grinder. 



So here is a finished port (right) versus an untouched one (left).  Jeff took care of the knife-edged port dividers with a bull nose finish, which will actually help flow and reduce the potential of cracking in that area.

Now, notice the rough edging inside.  Also counter-intuitive, an overly smooth surface does not help flow.  That roughness helps make the boundary layer of air—which is the slower moving air—thinner, and by making it thinner the overall flow is increased.  Gerner put it well.  “If you look at a golf ball, the dimples on it not only helps players get control over the ball, but they also let the ball fly further,” Gerner explains.    Those dimples or—in our case, the new roughness inside the port—actually reduces drag.


This shot shows Gerner's work inside the ports.  The port work done by a previous shop had left the port floor with a sharp, 90-degree turn where the floor transitions to the back of the valve.  But, as Jeff put it, “you want to keep the port floor radius as broad and smooth, as well as shaped as closely as possible to the port roof.  This keeps the portion of airflow that is attached to the floor from coming unattached as mixture velocity increases.  If the column of air moving through the port can't transition smoothly, it becomes turbulent with a very negative effect on flow.  And, since the fuel is now involved as well, the smooth transition aids in keeping the mixture homogenous, and discourages fuel separation.”  This looks similar to what Boost Logic does to its oil pumps, as featured in Part 2.


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