Fortunately, most engines usually are relatively insensitive to plug location as long as the gap isn't moved too close to the piston. Which raises an interesting point: The common practice of shaving material from the cylinder head's lower surface not only raises the compression ratio, and thus the thermal load on the piston, but it brings the plug gap close to the piston crown -compounding the problem. A better approach to obtaining
increases in compression ratio is to purchase a cylinder head developed to do the job properly. Yamaha's GYT-kit heads, for example, provide the right compression boost, have their spark plugs properly located, etc. Other made-for-the-job cylinder heads offer the same fundamental advantage, which is that you get to buy a lot of other people's engineering at a very low cost.
