Sooty residue look from cowling exhaust...how do I do it?

how about ground-up chalk pastels? you can even just file away some pencil lead/graphite and use that. just brush that stuff on, presto!

Great idea, I'll give it a try and see how it works. Thanks heaps.

...and to the forum.

Tamiya Smoke has worked for me in the past-- but now I use Doc O'Briens Weathering Powders with awesome results....see here:

The color of exhaust stains on a radial engine will vary from engine to engine because of the way a particular carburator is set up. An all black stain indicates the engine is running very rich, while an almost white stain indicates it is running lean. I usually apply a base stain of black using thinned flat black applied with an airbrush. I then apply a very light grey pastel chalk to the center area of the of the stain which fades into the black leaving a gray stain outlined in black.

If you're skilled with an airbrush, that's the most permanent method. I wouldn't use graphite, that looks too metallic, but chalk pastels are great for this. They feather nicely and if poorly applied, you can just wash them off.