Yeah anything with a barrier layer is off to a bad start with heat conduction so while you can add area it would be better if the main head is one piece. This is why the japs cast the barrels around the sleeves and why inserted sleeves aren’t as good as std & in turn why straight cast ally plated was better still, not that there are many bucket motors like this.
Sorichio Honda liked to think of himself as a pure engineer. He was determined to keep the old race engines aircooled as the air was what was doing the cooling of water; so why have the water & all the complication?
. . . He was wrong about 4 strokes too.
If you make any head the common mistake is not to use enough material near the sealing surface. It needs to be substantial to cope with temp variations without warping.
With plugs, don’t expect them to shed any real heat.
As far as type go I agree with Mike to an extent, but disagree in other points. I think the plug needs to suit the combustion condition it is in, a bit like fuel really. No point having high octane in a low compression engine.
In my H100 it was air-cooled & comparatively low revving. So I didn’t push the com up too high but high enough. On the std ignition it burned through plugs, a CR ign stopped that. Then I experimented with different plugs on the dyno. No extra power at all. The system was good enough as was for the situation.
However on my MB50 with same ignition a smaller chamber, more revs & higher com it picked up over ½ hp with a fine wire plug. I’ve seen another bike pick up ½ (or was it a whole) hp with a fancy shmancy $80 racing plug.
But despite being the same type of engine with same ignition, revs, fuel etc, the same plug (I borrowed in the same session) made no difference in mine. There were reasons for that, but the point is experiment.
Also the EGVs are fine, been using them for years in the 50 & various other bikes of all capacities. I think it is the EVs that are for tuning or some-such. Dropping ends do occur with normal plugs in some bikes like RM250s etc from vibration & they need special plugs.
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