Most forges I see have smaller burn chambers, Is that for efficiency/ easier to maintain temp? And for the round forge I am building, I plan on using two "T-Rex style" burners, which are supposedly more efficient than what I'm using now, the depth of my forge chamber will be about 19-20" how far apart and where, (Front, center, back) should I locate the burners?
Yes, forge sizes are generally sized for the biggest work intended to be done in them, and because venturi burners don't heat as well or as efficiently as a blow burner, the forges using venturi burners are smaller by necessity. Honestly, there is nothing efficient about venturi burners compared to blown burners.
Yes, you will likely need a 30psi regulator, IF you every intend to get welding heat out of a forge with venturi burner(s)
I'm not going to attempt to answer the question about where to put the burners, simply because getting multiple venturi burners to work well/correctly, in the same forge is nearly impossible. To explain, I'll concentrate on a two burner setup here.
When fed off the same fuel supply, one burner will always get more fuel than the other, meaning one burner will burn hotter than the other, and all the things that go along with that occur. I've seen people waste literally months and months of their time goofing/trying to adjust multi venturi burner forges......and they never can.
Those who tell me they have a multi venturi burner forges that are "adjusted just fine", are ones I don't even bother trying to help, because they either have no clue, are are simply in denial.
The ONLY time I would recommend a venturi burner, is for a single burner application, and then for someone who will never require "welding heat", and/or who needs a forge that either requires no power, or must be portable. The placement of a burner depends on the given forge design, but for round, horizontal forges, a burner/burners should be positioned like depicted in the article above.... centered just below horizontal center, with a pronounced downward tangent/angle to the intake end of the burner. I single, correctly sized venturi burner, with a correctly sized forge interior is capable of heating approx 14-16" of interior length.
So how does one make a multi burner venturi setup work correctly? The only way I have ever seen it accomplished is to have completely separate/independent fuel systems to each burner, then each burner is adjust as if it were the only burner. Everybody has this fantasy that using a "T" to supply a single fuel line to two burners means they must be getting equal fuel.....and it's just not true. The line to one burner might be a bit longer or shorter then the other, the ID might vary, one burner may be "sucking" in more air...... or any of a hundred other things....but two venturi burners, running off the same fuel line never get the same amount of fuel. That means there will be hot/cold "spots" or "areas" within the forge. No big deal if general forging with "mild" steel is the intent, but it can be the difference between success and failure when it come to forge welding, or using alloys that have very narrow forging temp ranges.
I have no idea why so many beginners gravitate towards venturi burners....they are far more complicated, far more finicky to work with and adjust, and consume far more fuel than any blown style burner. Maybe it's back to the "lemmings"? I do use a venturi burner, but is is a single burner, in a small forge, used ONLY for general forging of knife steels...... on it's best day, it will top out at about 1975F.
Based on the pics you posted, I suspect that your forge is far too large for the burners you have. I would say that you are either going to have to down size the forge itself, or up size the burner(s).
When it comes to forges, it's always best to make/use burners that larger than what you think is necessary. That's because you can always "dial them back", where as if you the burner(s) are too small, and you reach the peak/top end of what a burner will put out, your only option then, is to buy or build a larger burner.
Sorry for being so long winded, and disrupting the flow of this thread!