3rd Gen RX-7 Top-feed Secondary Injector Mounting Solution.

 

 

 

I chose to use 160lb (1680cc) injectors in the secondary position on the fuel system for my '93 RX-7. Stock secondary injectors are side-feed style, so in addition to making a fuel rail I also had to figure out how to seal the injector to the lower intake manifold (LIM) satisfactorily. The stock setup worked by totally sealing the fuel side of the injector within the fuel rail "shell" and then bolting it to the LIM. Inside the LIM was a diffuser used to further atomize the spray. Manifold pressure doesn't leak by virtue of the fact that the fuel rail is bolted over the injector bore.

 

When upgrading to top-feed Bosch style injectors most people remove the diffusers to fit their injectors into the bore.  The resulting fitment doesn’t lend itself to proper sealing and so the recommended solution has been to cut a piece of 5/8” ID hose and place this around the injector.  This helps to stabilize the injector and also seal it.  It has been referred to as an “Insulator” although it’s really a make shift injector seal.

 

While this solution may work, it didn’t pass my sniff test.  It just didn’t smell like the proper solution.  The injector’s o-ring isn’t properly sealed and this leaves a lot up a piece of rubber fuel hose. What I did was machine a slip-in bushing to adapt the stock injector bore in the LIM to the standard sized 14mm o-ring bore.  This way the injector o-ring seals properly and fits the way an injector was supposed to.  There is enough of a shelf at the bottom to retain the injector.

 

 

Here's an image of the finished product.  It doesn't look like much but the devil is in the details.

While making a set for someone who asked (Gene Felber, you can see how he used them here), I made a small run of these and am selling them.  One pair, shipped to the US for $25.

*** UPDATE 6/13/05 *** I make these upon request now and can always find the time to make a few sets. Please add what year  LIM you’re installing them into in your paypal.

--Dave

 

 

 

 

If you'd like to turn your own, here are the dimensions that I used.

  • The height isn't very critical and these fluctuate between .31" and .325".  
  • The outer dimension needs to be fairly exact although minor mismatches can be overcome by freezing the piece before fitting if it's too big or gluing if it's too small.
  • The ID can fluctuate from .530 to .540 and still seal well.
  • The bevel could be anywhere from 45 to 75 degrees.  It just helps to ease the o-ring into place.