[jlhansen]

What I was referring to regarding carbon, apart from the detonation, is that it tends to fill in grooves and other irregularities in the chamber. I have never cracked the head on an engine newer than 1980, so I'm not sure what kind of problem carbon is now. In the older engines there is a coat of carbon that would nearly fill the end of the grooves and make the whole thing different than intended.

On the other hand, I don't see the black tailpipe residue on my Focus, so things might be different now.

The intake turbulence is definitely a well-documented desire and I've seen the gamut of intake treatments from polishing to not polishing to swirl-finishing to impeller installation to "tumble flap" installation. I'm sure it all comes down to what actually happens and how long it keeps happening. Any complex system is only as strong as the weakest link. If the weakest link is robust enough to last, then the system is a winner.