Dimensions conflict

Hello everyone

If I follow the 1:1.5:3 (Wisner's) or 1:2:4 J tube ratio suggested by Glenn Hebert the barrel seems too close to the feed tube.



This is my revised mock up after realizing (with help) that my burn tunnel was too long.
Check out my main build post here for additional info.
I am not finished building the heat riser. This is the internal pipe only.



If I center the barrel it seems to close to the feed tube.
Do I give the back side(move barrel to the left in above image) more space so the exhaust exit has more room and leaving more space for the feeder?
And if I can move by how much can I move it?
The external tube is 15" (not cut yet).

What are you using as "1" in the ratios? Peter van den Berg in I think the donkey32 forum said that it could probably be between 0.7 and 1.3 times nominal system diameter. From your pictures, it looks like you have an 8" system, and the burn tunnel roof is the same as the feed tube opening, around 7.5". The E & E standard build uses four firebricks for the burn tunnel roof, giving 10" here, which is sufficient for easy clearances with the barrel centered. You can offset the barrel as long as you leave at least 1 1/2" to 2" gap. You will get more airflow and more heat on the side with the wider gap, which can be used intentionally to tune the output characteristics.

"What are you using as "1" in the ratios?"
Is this what you mean?
Feed tube : tunnel length : heat riser
I am using what E&E suggested in the DVD unless I calculated it wrong.

And yes its an 8" RMH system.

"...it could probably be between 0.7 and 1.3 times nominal system diameter."
Sorry noob here. Not sure what you mean.

The whole J tube is 7" x 7"
My heat riser is 32" + 11" depth of heat riser tube
Starting from this I calculated the rest

1:2:4 gives me 10.75 : 21.5 : 43
1:1.5:3 gives me 14 : 21.5 : 43
This is basically what I have now.

Since my heatriser exterior is 15" (barrel is 23)
I am left with 8". I guess I can put 5" on one side and 3" on the feed tube side.

A 7 x 7 burn tunnel is for an 8" diameter system. You could make the dimensions 6:12:24 or 8:16:36 or 10:20:40 or 12:24:48... as long as they are in the right proportions. Larger lengths will give more power to the rocket effect.

I understand how proportions work. Since my inner riser tube is kind of fix, if I wanna keep my proportions correct I can't very much play with the other two.
Unless I rise the heatriser with bricks.

Inner heat riser tube is 5/8 steel. I don't have a torch to cut myself.

I assume that no comment to other stuff means I didn't write anything overtly incorrect.

Thanks Glenn with your patience with my noob questions.