I have used a lot of smell additives in nitro engines but not in any gasoline engine yet. Their smell is strong if not mixed right, the Cinnamon will burn your eyes and the Cotton candy makes me think something is on fire. I haven't smelled the root beer. All of the fruit pretty much smell the same. Kind of like a blow pop :thumbup: I have seen that they do accumulate a lot of suit on the exhaust and on the car where the exhaust comes out.