Don makes some good points about the length of the run and pressure. I'm recommending double the holes based upon the tight hole formation in weber grill burners and the ability of those burners to stay lit. If you have the pressure, then I'd say drill out more holes.
Heat accelerates oxidation/rusting in steel, so theoretically, very thin steel plate might rust faster in the deflector role you're considering for it. I believe 'aluminized steel' is made to counteract that. This being said, I really don't see 1/8" or thicker steel ever rusting through at these temps. Any good design should give you burner access, so, with that access, you should be able to check deflector wear as well. If you do see any rust, go with ss next time. For now, though, I think you'll be perfectly fine with regular steel.
I don't think I've got enough pressure to double the total aperture of the ports. The gas comes in 25Kg cylinders that they tell me is high pressure. Its a little more than my home gas but not a lot. Maybe I could double the number of holes but make the new one 1mm instead of 2mm?
The reason I liked aluminium was to spread the heat. I know that's what 'deflectors' are for but I want to really
spread the heat evenly.
The possibilities for a stone hearth are limited. Fire bricks look like the best option atm. On closer examination of the imported 9"x9" ones available I found out they are 2.5" thick. As there will be about 20 separate bricks for the hearth I want them to be heating up at the same rate (trying to avoid hot spots). Therefore aluminum looked good.
I'm now thinking along the lines of: 3mm steel plate, topped with 6mm aluminum, topped with the fire bricks. Overkill on thermal mass but ........ The other thing I have been thinking is to make the surface of the aluminum act like a stone, i.e. rough it up: and use that as the hearth. Aluminum is not very hard and causes Parkinsons Disease. So maybe steel aluminum steel sandwich and rough the top layer of the steel up. Just thoughts!
More holes is a good thing...they should stager at an advantageous/opposing angle though. Still gonna need fuel coming in at the a$$ end ..too long of a run no matter how much psi you present on the front end..IMHO of course..
Like the idea of staggering them - make sense.
In you're next post Bob, you saay choked up. The control systems I'm looking at all have a blower to pump air into the burner. Should sort it out. Just don't really like the look of my burner after having seen the weber with millions of holes burning perfectly evenly!!