How to make a collector using 304ss 1.5†schedule 10 pipe for a T3 flange.
This is meant as a guideline for building a collector. Always put safety first and wear proper PPE while working with tools and equipment. This is only one way to make a collector. Everyone has their own method, but I have found this way works for me and perhaps it can help you too. I use a vertical band saw, but the same theory can apply to a vertical band saw or a chop saw.
1.Decide on the length and angle of your collector. In most cases, a longer collector with a more gradual merge angle is ideal, but sometimes space does not allow for it.
2.Cut all your pipes for your collector. I set a stop at one side of the table to ensure all the pipes are the same length.
3.Face the end of the pipes and chamfer. I use a lathe, but a belt sander can work too.

Be sure to deburr the inside of the pipe after this step.
4.Measure the distance across the short side of your turbo flange inlet, divide that # by 2 and this will be the distance from one side of the pipe that you will cut your angle to.
5.Set up your saw to cut the first angle. I like to put a stop on one side of the pipe to butt it against so they are all consistent. I use some vise grips to hold the pipe while cutting so to avoid losing any fingers.

6.After the first angle is cut on all 4 pipes you may be left with a small step at the end of the cut.

To flatten it out I just put it on the belt sander to smooth the last bit out.

Here is a comparison of before and after.

Be sure to deburr the inside of the cut as well.
7.Wire brush your pipes at this point. I use a brass wire wheel on a bench grinder that I only use for stainless pipe. Using it for other materials can contaminate your stainless when you weld it.
8.Tack weld two of each of the pipes together in 4 places. I use a couple blocks on the welding table to keep them from rolling away from each other.

9.After your two pairs of pipes are tacked together the next angle will be cut for the bottom of the merge that meets the flange. I typically eyeball the distance from the midpoint of the inlet in the flange to the top of the lip of the pipe so it will lean far enough away from the center of the flange inlet so it doesn’t interfere with the other pipes. This pipe is cut, but it gives you an idea of what is needed.

For the setup on the saw I use two stops clamped to the table. The first stop is used to lift the pipe merge to the desired angle. The second stop is used to keep the cut length consistent between all cuts. Here are some different angles during the cut.



10.The third and last angle only requires one stop on the saw, since the bottom of the merge is flat to match your flange inlet. I choose to do it standing up just because I find it easier, but it could also be done lying the merge on its side with a spacer under the narrow end. Here are some different angles of the cut being made.



11.The end result should look something like this, but you aren’t finished yet.

When you lay the flange over top of the collector pipes it should sit flat and if your measuring was on, it should poke inside the inlet slightly on the sides.

There are a couple different ways to flatten these out. One way is to just squeeze the sharp points flat in a vise.

Another way is to partially weld the pipes to the flange and use the round end of a ball peen hammer and hammer them out to match the port in the flange. I usually do this to push the pipe out of the port in the corners. The end result should look similar to this.



12.The finished collector should look something like this.


Usually, I leave the collector unwelded until I know I don’t need to break it apart to build a particular manifold it is being used for. Some people prefer to weld them up right away, but sometimes haste makes waste.
I hope this helps, good luck!