Here's a good tip for cheaply cleaning the valves, pistons, and cylinders. Raise and rev the engine RPMs while only dribbling very small amounts of water into the throttle from a bottle. Done right, the engine will only stumble some, but the carbon on valves and in the cylinders will be caused to break up and burn off and out the exhaust. I only use the fuel additives for cleaning injectors. If you added water injection, you would have continuous cleaning action and no need for expensive boosters. Water injection uses cheap methanol based windshield washer fluid - about $3 a gallon. Water injection was good enough for WWII aircraft - and it still works great. The Booster additive people would prefer this was unknown.