I think the most important part to getting the smoke is killing the engine by having it suck in too much.
The times I ran Seafoam and didn't kill the car by that method (or wasn't able to, as was the case on my friends Impala,) we didn't see much for smoke.
The times I did see results all were when I killed it first by drowning it, then had problems starting it back up, and sounded like it was running on 5 or 6 cylinders after it finally started.