Interesting discussion. My first thought was that increasing the surface area, say by cutting little grooves in the coolant passages, would improve heat transfer. But I'm not a mechanical engineer, nor did I ace thermodynamics some 30 years ago when I was in school for my BSEE, so I have no idea which of the techniques discussed above (individually or in combinations) would be most effective.
Barry - were those wall temp curves something you generated yourself through testing or were they found in a reference somewhere? Would be cool if someone with an ample supply of housings, appropiate test equipment and skills could rig up a test to do a comparitive evaluation of these techniques. What I'm thinking is the housing can be installed in a test jig that allows coolant to flow through at a controlled rate. A torch or similar localized heat source to heat the area of the plug holes on the housing, which would be instrumented to measure & map the temperature distribution of heat applied. Then simultaneously measure & map coolant temps as was apparently done to generate those curves. The curves would then answer which technique or combination nets the best result.
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