You can get SOME smoke out of any engine. You won't be happy with the smoke output with less than a .60 2-stroke. A .50 size 4-stroke can do OK.

The simplest pre-heater is wrapping a few turns of copper tube around the header on the 4-stroke... or atound the cylinder on the 2-stroke. (I've seen one guy use a boat type water jacket for his pre-heater on a .15 2-stroke...) Better pre-heat does equate to better smoke.

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There is an ongoing debate about whether the smoke devices being sold (and advertised as approvable by AMA safety code rules..) are actually allowed by the AMA safety code... They are not specificly listed as an allowed type of pyrotechnics. They don't meet the definition of "smoke bomb" which is specificly listed as NOT allowed... Because its not clear... you will get different opinions at different airfields. Some will say to go ahead and use them, where others will take a more litteral view of the allowed pyrotechnics list. (It isn't on THAT list... its not allowed.) The ones who go by the litteral listing will be in a better position to defend thier decision then the ones ho allow it.

I would hold off on buying smoke cartridges until the debate is settled.