I Like Toyota's implementation. to correct this gdi carbon buildup issue you need to spray something before the intake valve. so it can be constantly washing the intake valve while the motor is running. like the way it used to be. All the detergents in the world added to fuel won't help with this gdi issue. but it doesn't have to be fuel. you can just get a water injection kit. or 50/50 water and meth if you like and are boosted. Or just get a functional ram air and drive your stuff in the rain once in a while. for the heads/cam package install I like to run water through an iv drip into the intake and clean the inside of the motor before teardown. just to ensure a clean outcome. and that i'm not bolting a fresh combustion ceiling on top of a nasty floor. there is no reason to not do this. water is free. and how much better will the initial outcome be without any carbon buildup anywhere?
And carbon doesn't scratch cylinder walls guys. this statement suggests that you can get fuel to harden to the point of steel. honestly. more likely that cylinder got hot and was scratched by a ring. for that one cylinder with a scratch on it, over your lives how many carboned up pistons have you seen in a smooth bore? crosshatching gone maybe, but no scratches. if a motor could reach a point where carbon could hurt the cylinder bore, then at that point just the piston rings and piston sliding up and down would rapidly erode and destroy that cylinder.