I put in 2 cans.
It was on sale for the same price at my local parts store also.
YETTI-
It doesn't smoke at all when added to fuel. Only when you suck in the manifold with a vacuum line.
You can also add it to your oil a day or two before you change it.
NOt sure if you'd be doing things backwards if you cleaned your injectors/fuel system first and then added it the oil before an oil change.....