For gasoline, the change of state from an atomized liquid to a vapor is endothermic -- it absorbs heat. The resulting temperature of the fuel/air flow will depend upon the amount of heat available in the endothermic zone. Under the right conditions it is possible for the temperature of the endothermic zone to be below the freezing point even with ambient air temps as high as 90 degrees F. Worse-case, you may need more heat than you've got.
In many cases the waste heat from a single cylinder of a 2180cc engine, 8.5:1 cr, engine isn't enough to keep the endothermic zone above the freezing point. Just as there are hypereutectic thermal barrier coatings that can keep the heat inside your exhaust pipes, there are thermal disbursant coatings which enhance the heat flow out of a pipe (or cylinder head). Used in combination you can effectively focus your waste heat inside the heat exchanger for your carb or cabin heat. (I'm using Tech Line's thermal barrier coatings. I've no experience with any of the others.) I've found stainless steel pot-scrubbers to be the best labrynth media for the heat exchanger (as opposed to door springs, etc). I've also found that spot-welded body-panel studs make the best radiating elements, assuming the entire assembly (ie, pipe & studs) is coated with a thermal disbursant (which also prevents rust). Finally, based on a 2180cc engine running 7.5:1, to provide sufficient heat for the worse-case scenario (ie, low temp, high humidity), I needed approximately 95 square inches of exhaust pipe surface, fed by two cylinders, to ensure an ice-free endothermic zone (ie, 90*F over ambient). YMMV. -R.S.Hoover
