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Modifications to L28 intake for 440cc injectors


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Hi guys, first of all, I never post on here because I usually find what I'm looking for but this time I haven't found an answer. For those of you that have upgraded your injectors (and it seems that most of you have), what modifications did you do to the intake manifold? The 440cc Supra injector nozzle does not fit into the L28 intake plenum. I haven't seen this addressed in any other post, so maybe I missed it or I have the wrong injectors. Can anyone elaborate on what needs to be done? I'm guessing drilling out the holes to a larger diameter but then what o-ring gets used? Side note: I'm also using the 240sx throttle body and it's round like most throttle bodies, however, this L28 intake has a teardrop-shape intake port where the throttle body goes. Thus, there is a gap at the tear drop pointy end that isn't covered by the throttle body. Does this mean I have to use a spacer, even if converting to a cable line? I read somewhere that if you flip the TB, the cable wheel can be used on the opposite side and the spacer isn't needed. Don't see how that works. Any guidance will be appreciated. Also, if there is a post with SPECIFIC information on this, please let me know. Thank you in advance.

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  • 2 weeks later...

It depends to a certain extent on how you have the injectors attached to the rail.  The Pallnet rail has the injector o-rings inserted in to a cavity to seal the top and uses the precisely machined mounts to press the bottom o-ring against the manifold surface.  The bottom is not the typical o-ring seal, it uses downward force to create the seal.  If you don't get the rail mount correct, and the sealing surface flat and clean, you can have a vacuum leak at the interface with the injector.  Coincidentally, a typical o-ring style injector will project in to the flow stream of the L6 manifold at just about the perfect level for injection.  Not too deep or too shallow.  You don't have to use o-rings either, you can use the Nissan sealing rubber instead.

 

A more typical aftermarket mount would fasten bungs to the manifold to create a technically correct o-ring seal.  But the downward force method works on the bottom because it is only sealing intake vacuum, not fuel pressure.  It's not ideal but it seems to work fine for a lot of people.  You can find injector bungs everywhere if you want to be more correct.

 

https://www.jegs.com/p/JEGS/JEGS-Fuel-Injector-Bungs/3318814/10002/-1#

 

image.png.22efb4707d79a9fb0002e80e385b4dfc.png

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Thanks for your responses! What i ended up doing is taking off the fuel injector pintle cap from the old 280ZX injectors and installed them one the new Supra injectors with a thin file of silicone (just like the stock ones had). I drilled out the hole to be similar in size to the Supra pintle. I am not 100% sure if this will work, and seeing as the car is still a few months away from being complete, I won't be able to test for leaks. I've yet to see anyone have this issue or address it if it was an issue, so I am going under the assumption that these were not Supra injectors as shown in the listing I bought them from. I'll update when i get it going.

 

As for the intake manifold/throttle body, I think I need a spacer regardless if I'm going the cable route. The spacers I've seen have more of a rectangular shape to them rather than square, which I assume is to cover that extra opening area. Again, I haven't seen anyone address this issue but I did see someone who had a similar question with no reply. Considering these are both fairly common (or discussed) mods, I'd assume there'd be more info on these nuances. Nevertheless, where there's a will, there's a way. I'll end up machining a plate to cover the area and push the TB out more. If anyone knows where I can buy one, I'd appreciate the link. Arizona Z didn't respond to an inquiry to purchase, Godzilla is out of stock.

 

Here she is below in her L24 glory...

IMG_5529.PNG

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