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Old 11-10-2012, 08:07 PM   #679
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OK, I had just a little bit of time to work on some things while the wife was sleeping this morning before I had to clean the house.

Earlier this week, I was able to stop by my machinist and pick up some parts that he made for me based on designs I gave him. The parts were to adapt the USDM throttle body and fuel fails to the JDM V8 intake manifold that came with my EJ207.

For the throttle body, there were several differences between the JDM manifold and the USDM WRX/STi manifold, but they all centered around the fact that the USDM WRX (06+) and STi (04+) are 32-bit ECU's with a drive-by-wire (DBW) throttle body. The EJ207 through at least Version 9 uses a drive-by-cable (DBC) throttle body on a 16-bit ECU, much like the 02-05 WRX. These two systems have some pretty big physical differences both on the throttle bodies and on the intake manifold. The differences are big enough that they two are not interchangeable without some serious work.

I have to keep the DBW TB because of my 32-bit ECU, that was non-negotiable. So my choices were to use the DBW intake manifold from my WRX or an STi, or do some custom adaptation work on the JDM intake manifold to make it plug and play. I chose the latter option because the JDM intake manifold is a straight runner (no TGV's) compared to the USDM manifolds which have the secondary TGV castings. The JDM unit is a lot cleaner and leaves way more space for inlets and hoses and things.

You can see in this picture how much more bulk there is with the USDM TGV manifold on the right versus the JDM unit on the left. And that's without all the extra stuff cut off the JDM manifold like I did.

Anyway, the problems with the DBW TB are as follows:
  • The DBW TB motor assembly protrudes beyond the mounting plane which means it hits the JDM manifold.
  • The JDM manifold has a cut/open section for the idle air controller on the DBC TB. This would leak with the DBC TB. Like a lot. The DBW TB doesn't use/need this separate hole.
  • The DBW TB uses M6 bolts, the DBC manifold needs M8.
  • The DBW TB mounting hold spacing is different than the DBC TB (holes don't line up).

Here is a picture of the USDM DBW intake manifold TB mounting area. You can compare it with the red JDM STi manifold in the picture above and see the differences. Notice how the USDM manifold is raised to allow the DBW TB to not contact the manifold.

A picture of the DBW TB overhang:
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Last edited by kpluiten; 11-10-2012 at 08:40 PM.
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