speaking of cleaning bores - if there was a way to clean the air injection ports on my 993 with some kind of cool brush like thing, that would be a great boon - and it would be something that could be sold widely - these cars are infamous for having carbon block the ports, leading to a MIL light and then (if you are the typical "clean hands" type owner), a $10,000 service charge to pull engine, pull heads, and rebuild.
the ports are between 3/16 and 1/4 inch in diameter and are above the valve stems, so you can see them (barely) once the exhaust manifold is pulled. they go into passages cast in the head and the carbon builds up in these twisty little passages. There are FAQs on the web about how to clean using injector cleaner, but this is not totally effective.
There is access by going up into the ports (around the valve stem), and there is an aprox 3/8 ID tube that carries air into the heads for injection - but I have no idea what the internals of the passages in the heads look like. the "mini-snakes" I have been able to build won't clean it out, though on occasion high pressure air and enough solvent will.
here is a link to a FAQ about this with some photos that may help explain
so, here is a new project for those who are inventive and knowlegable.