So with both throttle bodies and both manifolds in front of me, I sat down and used CAD to think up an adapter solution. I could have chosen to have the JDM manifold welded up or modified to work, but I really wanted a plug and play solution that required no welding/cutting/grinding of the manifold or the throttle body. My thinking was that this solution might be useful for other doing this swap and perhaps I might sell this solution in the future. For those curious in the alternative, Amroof had his manifold permanently adapted by welding on a new mounting plate and it turned out really nice.
This is what I came up with: A two adapter plate method. In a nut shell, one plate mimics the hole pattern of the JDM manifold and the other plate mimics the hole patter n of the USDM DBW TB. The two plates share coming holes between them to join the two together. Together, they provide enough offset to prevent the DBW TB from hitting the manifold.
I also designed the plates so that the two could be mounting in several different orientations relative to one another so that the TB could be clocked for various turbo/fitments depending on setup (it's not uncommon for the DBW guys to rotate their TB 180 degrees for larger turbos).
The setup uses factory gaskets for all three joints with only minimal modification to the middle gasket between the two plates (adding 8 holes). This ensures a leak free system without expensive custom gaskets or messy sealant.
Here is the base plate that attaches to the JDM manifold:
Bolts added (low profile hex key bolts):
Plate lifted off the table so you can see how the bolts fit in the counter-bores. At this point, the plate would be mounted to the JDM manifold, but mine is at the powder coater, so use your imagination:
Gasket for sealing between the two plates. I used a DBW TB gasket and added 8 holes for the next set of bolts (the radial pattern around the center hole).
Top plate added. This plate mimics the hole pattern of the DBW TB (outer four holes).
Bolts added to fix the two plates together. Notice how the two plates could be roatate or clocked at 45 degree increments relative to each other.
A DBW TB gasket installed to seal between the TB and the adapter:
DBW TB installed:
(Sorry for the bad picture)
Another shot. I made the TB plate smaller so that there would be no issues plugging in the sensor plug. But the manifold plat needed to be larger/longer like that to cover and block off the secondary idle air controller passage on the JDM manifold: