Lionel's new premium smoke fluid and the newly designed wicking seems to be the best solution for producing copious amounts of smoke. I have one of the Lionel PRR M1a's, the early production, and after replacing the wicking and using the new Lionel smoke fluid it almost rivals an MTH smoke unit. Not other modifications were made to the smoke unit itself.
I am running under full command so I have 18 volts to the track through a Lionel TPC 300.