additives are very legit, and the Chevron "Complete Fuel System Cleaner" listed above is a favorite due to its high concentration for relatively cheap price. You can read to your heart's content on this subject over at the bobistheoilguy.com forums. I also really like the BG 44K product, though that product's formulation is more of a mystery. It is also way more expensive, around 30 bucks a can.