Fabricating an Intake Manifold for a  Ford Turbo 2.3

In my quest for more power out of the 2.3 in the rail, I had few choices.  I could put a nitrous kit on the engine and get a bunch of power on demand, but I'd have to make sure to fill the nitrous bottle before every trip, or I could add a Turbocharger.  Since the venerable 2.3 came turbocharged in the Thunderbird, Mustang and Merkur, parts to add the turbo are readily available at local salvage yards and a retro-fit should be relatively easy.  I, however, do not like to make things easy on myself,  so rather than using stock parts, I decided it would be a good idea to fabricate my own intake and exhaust manifold. 

The Intake Design
Having few size and interference constraints compared to a stock engine compartment, I was free to design what I believe to be an optimal intake manifold without having to worry about fitting it under a hood.  I began by reading Bell's turbocharging book and studying pictures of intake manifolds on turbocharged race cars.  I landed on a design that seemed to be fairly common in the race world, that of a curved plenum with an individual runner to each cylinder and a throttle body mount on one end.  The plenum volume was calculated to be 80% of the displacement of the engine and the runner length was chosen as a compromise between a long torque-enhancing length and a short high-rpm length. 

Here's the pieces for the intake, including runners, plenum, base, end caps and throttle body flange. Not shown is the flange that bolts to the head.  That was cut from 5/16 steel with a plasma cutter and then ground to fit the head ports and runners with an electric die grinder and carbide bits.
Where the intake runners join the flat part of the plenum needs a generous radius to allow for good airflow.  Figures that I have seen show an improvement of anywhere from 40 to 70% increase in flow with a good smooth radius.  Velocity stacks are one way to go about obtaining this curve, but I chose to make a quick tool out of aluminum to dimple the flat plate.  Here's a pic of it shaping up in the lathe.
I made a top and bottom to the tool, the top looking like the above picture in the lathe, the bottom has a cavity that mirrors the top with enough clearance for 1/8" steel to be pushed into it.  Here is the tool in the press, and 20 tons  was just enough to nicely dimple the plate.  We were wondering if the aluminum tool would be up to the task of dimpling steel, but it held up very well and is ready for the next time I need it. You can see the decidedly lo-tech way we located the runners on this part by the spray paint image of the intake gasket. 
Here's a shot of the dimpled hole.  It is difficult to see, but there is a substantial radius on this piece.
The dummy head with the intake flange fastened to it to prevent warpage while welding
The welded runner/flange assembly
Here the runners have been welded to the plate and the radii almost smoothed out. This took a while with a carbide bit and the die grinder, then moving on to a sandpaper cartridge roll for the finishing. Interesting thing about grinding steel when it is hot:  little sharp bits of metal fly off the bit and stick to your sweaty skin, then proceed to rust. It makes nice orange stains on skin and clothes. This pic gives a better indication of the size of the dimple.
The polished and smoothed radii ready for assembly.  This should offer quite an improvement in airflow over a straight butt-joint.
Now the curved part of the plenum has been welded on, and the end caps fitted and welded
A side view of the completed plenum, at this point, the assembly was pressure tested and a small leak was found and welded.
Drilling the hole for the throttle body with a hole saw
Here's the mostly finished manifold on the dummy head
Again, and note the slight angle of the plenum, this should parallel the rear cage of the rail since the engine sits at a small angle. The surface that mates to the head was machined flat and true by the guys at R'n'R machine.  Apparently due to the welding the flange was harder than heck and they had to use a CBN tool in a mill to make it flat. 
Another view.  Now the injector bosses have to be welded into the runners and a pipe thread bung welded to the plenum for the intake temperature sensor. When that's done, I'll drill and tap some 1/8" pipe threads for lines to the wastegate, MAP sensor, Blow off valve and boost gauge.

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