I personally have never seen any independent proof that any product will really "drive our engines clean". Has anyone else seen any real world tests?

As to combustion chamber and valve cleaning, there are a number of very good products for that. But they aren't diluted in the fuel. They are poured in the intake tract while running or sprayed into the cylinder directly through the spark plug hole.

Combustion chamber cleaner or upper cylinder cleaner are a couple of names. GM has it as do most outboard motor shops.

It does a very good job.