My Turbo Outlet Adapter 

To fit the Turbocoupe Intercooler to the Merkur's stock turbo, there are a few options.  Since the TC Intercooler is the basis of my Air/Water Intercooler system, I decided to have a special casting made just to make this adaptation. I soon found out that  sand casting would be the only option that would be of reasonable expense.  I then set about making a mock up of exactly what I would need.
I had an aluminum adapter that was roughly similar, but not real close.  I ground on it with my dremel tool, and built up parts of it with an epoxy putty.  I fitted the TC Intercooler to my Merkur's turbo and duct taped it into position.  I filled the duct taped area with epoxy putty and let it harden.  I then ground it smooth and contoured it, building up and grinding down areas to get it just right.  I then cut it loose from the TC Intercooler along the original edge of the intercooler's tank.  See Photo.
I wanted to be able to fit a thermister to the intercooler later, to measure the turbo outlet temperature, before the intercooler, so I added a boss with a threaded plug in it.  I added a smoothe contour around this boss in my casting.
Then I took my part to the foundry and they told me that I needed to have a specific draft (taper of the wall) to the part, and would need a core print since it is hollow.  Basically, I would need a special pattern made from wood (of all things) and would need to talk to a patternmaker. :(  

The pattern maker used my part, but said that he really preferred to work from a drawing with measurements, not a real part.  Damn...all that work for nothing!!!  Anyways, the pattern was not cheap, but I had it made.  The photos below are the two halves of the part.  There is a third component called the core print which I did not photograph.  It basically is the same as the "void" in the part.

The "bulge" on the back of the fitting is not a casting sprue, but is instead my contoured boss for any instruments, etc... that someone might want to fit to the part.

This is a picture of the rough part.  I have it milled flat on the bottom side so it seals well against the turbo.  I also add the bolt holes.

What I like to do is weld the part directly to the intercooler, which eliminates the hose connection, which can be a pain when changing plug wires, etc..  I do this using a mock-up of the Merkur engine.  Actually, it is an extra head, exhaust manifold, turbo, and intake that I have from my parts car.