I plan on putting a smoke system in a new plane with a DLE 30 gas engine. I want to know if there is an advantage in using a special muffler (ie: with a coil inside) and if so, who makes one

I've never found a real advantage to it.

" I want to know if there is an advantage in using a special muffler (ie: with a coil inside) "

The purpose is to pre-heat the oil, so that you are not pumping cold oil into the chamber. I never used a special muffler on my 4 strokes, but I did wrap a few turns of copper tubing around the exhaust header, and use that at a pre-heater.

Having a coil in the muffler never really made sense to me - You are taking heat from your heat source to heat the oil which you then want that heat source to heat.

Kind of like robbing Peter to pay Paul.

Or like writing yourself a check.

Eloquently put !!