I once tried to make a turbine style retention head.Used .02" stainless steel. Length: Inside blast tube diameter times3.14. Wide: about .5" + length of the vanes. This vane lengthdepends on the diameter of the blast tube and the open space youwant to have around the nozzle. Now you can cut this piece of strip.The vanes are about .3" wide, but that's random. Less vanes willgive less swirl. Scratch the vanes and the line where the 90* or60* fold comes in the strip. Drill a .1" hole where the vane scratchends on the fold line. Cut the vanes towards the hole. Since theholes are all in one line, the cuts have all the same length. Bentthe vanes over the folding line in whatever angle you want. Twistthe vanes in the angle you want and align them. Carefully bent theremaining .5" strip in a circle. Put it in the blast tube and alignagain the vanes till you're satisfied. Some screws to attach it tothe tube.I did not fire it for a long time, because the flame pattern didn'tmatch the narrow recirculation tube. Lots of swirl in the first 10"of the flame though. It is an excellent head for short chambers. Thevanes didn't get hot, but wet with oil.