Hello, what do you think about these additives (brand Xenum, Mannol etc, always good brands), to add to our 550 v8 to help take care of the fuel circuit and combustion chambers so they last longer and work better, any problems due to the coating of our cylinders? Greetings!!!

Most car manufacturers advise against fuel additives (consult your OM on this). I use a fuel stabilizer in one of my cars that I store during winter (1 treatment / 1 tankful), but nothing else. Best practice is to use a quality brand fuel with the recommended octane rating from a high traffic fuel station that keeps its dispenser pump filters serviced.

Chevon sells Techron by the bottle, an additive that's already present in their gasoline. It won't help your valves if you have direct injection.