Wow, thanks for the quick responses. Here is the deal, I want the initial build to be large enough for
a stationary motor, either a twin cylinder 650CC Kaw motorcycle motor, or a 1500cc volkswagen motor,
(probably the bike motor) I think the bike motor is rated at about 30 HP, and the VW probably about 70. But, realistically I will probably mainly be using it for an 8HP generator at a remote worksite. (Eventually, I intend to do a system sized for a truck, and that is what I have actually been collecting materials for, but that is down the line). As far as the medium, I have about 50 acres of mixed wood, a lot of oak, pine, hickory, locust and hedge. I will be just rough cutting with a chainsaw or machete at first, and incorporate a rear axle/wheel rim chunker later on. While I like this kind of rough fabrication - have done it all my adult life, I don’t really want to have to redo it any more than I have to…so that’s why I’m here, to try to get some of this stuff worked out ahead of time, a kind of standing on the shoulders of giants type of thing. So, back to the questions. I know that there will be a downside to sizing the first one larger than what it will typically be used for, but, is that a huge problem? I have welders and torches, and am by trade a draftsman/designer, so I can work out all my designs virtually in 3D, and animate them - I can do that for you guys as well, if you have some radical new invention. But, most of the builds I have seen are using way too many airtight welds than I am comfortable with. I’ll wind up making just as many welds with my design, but I want to run as much internally as I can, to avoid leaks and aid in preheat, and to make the hearth and reaction zone modular, so I can change it out if I’m not satisfied with some aspect, or want to try something new, without having to do a whole new build. Also, since there is so much variation with diameters of found materials, which is essentially all I will be using, except maybe for the reaction zone tube liner. If I am successful with using a liner, then I, or others, can duplicate the design easily, without caring that much if the I.D. of their shells are 9" or 10", since I know as soon as I get one build, at least one of my neighbors is similarly inclined to build one of their own. Maybe I will try to get some drawings together to show my build concept, and you guys can critique it - kind of like a virtual workshop. Haven’t looked into what kind of attachments can be posted, or if there is a place on this board that these kinds of things are supposed to go. I should be able to export an .avi or similar. But, back to the questions. If I read the one response right, the kind of medium that I will be using will be best served by the hourglass shape - Is that the general consensus? Because, I am not adverse to the reduction style used by “Mr. Teslonian”, in his youtube Chevy Luv truck build, with just an overlapped smaller hole every time he reduced to another “tube”. In either case, it has been my intent to completely insulate around the whole reaction zone and reduction zone, probably even with refractory cement, depending on how that load is supported above. Maybe it will be best to just get some drawings togther. That probably won’t be till next week sometime, though. Anyway, thanks very, very much for all the help. Oh, one other quick question, is there a value in making the outer core fairly small to help the reactor maintain heat better, and create more turbulence? Also, should I make an effort in the outer core, with spiral shaped baffles, to direct the swirl the way I want it to go?