Charcoal cans have are more for better operation more than for power robbing smog control.
Even though it does help with emissions because it prevents raw hydrocarbon vapor from escaping. I never can understand when people toss those, used properly, that charcoal can could be your friend.
They certainly aren't any type of performance part, BUT, If it has the vapor return system intact, that whole system can save fuel by returning vapors to the tank and condensing them back to liquid fuel.
