I've actually seen this in action and it is quite remarkable!
Wing - tell us what you saw.
They had a car with half "other brand" and half v-power shell fuel. They had a scope and went right down to the valves on the engine. The valves with the v-power were CLEAN like new looking, the other fuel was gunked up and black it was remarkable!
So this was on the same engine? Interesting. How did they get the BAD fuel to go just to those valves and the V-POWER fuel to go to the other valves?? Having been tearing down engines for over 25 years, the only time I have ever seen carbon build up on the valves ,is on engines that have had 150,000km and have had valve seal problems.