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injector placement question... Tapp into upper intake manifold (RX7 S4 turbo)

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So my build is a bit unusual, but not unique. Some background to set the stage for my question and why I'm asking for advice. Im running a six port 13b in a '1980 Rx7. I wanted to keep the aux ports functional for a bit more midrange and possible cruise economy. This is not a track car but for the road. Turbo manifold is custom fabricated to clear the aux actuators. Originally I used the Mazda intake manifold that draws air from the right side of the car. this placed my IC tubing really close to the turbo and although heat management has helped, I am concerned about extended driving periods. Enter the S4 upper intake manifold that draws air in 180 degrees from the NA manifold/. I will need to make an adapter, which will likely be two pieces of plate aluminum with pipe/tube adapting the runners. You may have seen Aaron Cake build a very similar setup and this is where inspiration comes from.

This design commits the OEM N/A intermediate manifold that houses the secondary injectors. If I were to put the secondary injectors on the top of the upper intake manifold, at the 90 degree bend as the runners transition to the adapter I could have the injectors spraying at a zero degree dead center down the runner. My mind's eye sees this as a great location for the secondaries. Yet I have never seen this implemented, so I might be misunderstanding things.


Will work very similarly to stock, but in all honesty for secondaries on a boosted application so long as they're not wetting out, and are in the same location of the intake on both rotors you'll be fine. You don't have to worry about a reduction in velocity due to a 'wall' of fuel on boost as you would NA.

Thanks David, I was not familiar with the NA wall of fuel.. but after reading it, it makes sense. Thank you again for your thoughts

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