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This is a fascinating subject and is as Spuggy says, often counter-intuitive.
The "rough" surface of the tracts works like the dimples in a golf ball. the little eddies on the surface irregularities act like roller bearings for the charge hurtling down the 'ole. So the main air mass is not in fact so turbulent as in a smooth tract.
That would be counter productive on an exhaust tract as the little eddies would probably not pass the heat away so well as they will probably continue to hold the same air for a relatively long time and pass the heat to the head. Much as the water in waves doesn't move along but rather circles in the wave and creates the effect of a moving wave.
I was briefly involved with ERM (English Racing Motorcycles), they manufactured their own AJS and Matchless 7R and G50 engines and developed their own heads. The tracts were made in reverse out of wood or hard rubber and used to form the holes in the sand castings. The ones that worked the best apparently were long tapered ones like a carrot with narrow end at the valve whereupon they opened to a bulb shape behind the valve. It was always work in progress, as you don't necessarily know what part of the shape is having what effect.
Peter Williams Father (who's name escapes me atm!) worked in AMC's race department developing the 7R and G50 back in the 50's and probably earlier. He had a novel way to test the atomisation and mixture pattern of various tracts. He would line a cylinder with paper and rig a vacuum cleaner at the bottom of the cylinder. Then introduce a charge of air and ink via the tract and examine the paper to see the result. How he put the ink in I do not know. It would make sense to use a carb I suppose. That was the state of the art in those days... Good old human ingenuity.
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