Making a D port shape of 2" sch 40 aluminum

I want to make a D shape out of 2" schedule 40 aluminum (.154 wall 2.375 OD). Essentially flattening the bottom of the tube.

I thought what I would do is make a "half shell" of exhaust tubing split length wise and press it in a press. Didn't work at all. Exhaust tubing doesn't have the strength and it just crushed all as one.
I am now thinking I'll pick up some 2.5" schedule 40 steel pipe (2.47 ID), and split that length wise. Or, am I better off trying to anneal the bottom 30% of the aluminum pipe? I hesitate there, as what I am trying to do is make long tuned intake runners for a 4 cylinder, and so I prefer to have the aluminum hard, for rigidity, so that the 4 throttles don't go to far out of alignment.
The next hurdle is that some/most of the runners are going to have curves/bends, which is going to be a pain to do this way. I'm going to have to match the bend radius of the aluminum pipe in steel pipe, weld both and split the steel pipe lengthwise, them press the assembly.
The only other way I see is to cut the bottom off the runners and weld flat plate, and that's leaves me without the radiuses at the bottom corners, and the inside will have more sharp edges even if the welding is superhumanly perfect.

 

i think if i were trying this i would start by makeing the pipe oval first, then stand it up in you shell so when you press it the top would try and flatten some before it took the shape of your shell, i have made lacross sticks out of 1" sched 40 aluminum this way, do you have pictures of your setup?

 

My thoughts are to develop a simple timber pattern that has all the radius & shape requirements & make contact with a local Aluminum foundry, there is a reason that manifolds are made that way! If you develop the patterning yourself the runners will not be to expensive for a good result! Good luck

 

If you are going to have flanges on both ends of the tubes, you don't need anything anywhere need that thick. I made an intake for a turbocharged 4 cyl that used a stock intake manifold flange (made by cutting the original manifold off to make a flange), and the a simple flange at the other end to hold the four tubes in place. It slid over the ends of the tubes about 1" and then I weld it to the tubes for rigidity. Then I put a bead on the end of the tubes so short rubber hoses could slip over and connect the air box. I made this out of .065" wall aluminum 6061 and had the shapes bent first by a place called Tube Specialties in Huntington Beach. It lived under 15 lbs of boost and the vibration of a big (2600cc) 4 cyl in a rally car environment.

I had made an earlier version that used carburetors and the only difference was the flange away from the head was flush with the end of the tubes and was the pattern of Weber side draft carbs. It lived through 2 season of racing as well.

 

There is a guy on EBAY called ROSSMACHINERACING he sells what you're looking for.