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Discussion Starter · #1 · (Edited)
Multiple times I have read the mention of bringing original Opel 70s fuel injection systems into the modern age with programmable digital ECU, modern high pressure fuel system, etc.

I like this idea and want to do it.

Here is an example…
For 1.9-2.0 Engines you can use the 1975 Opel L-Jetronic Intake manifold and injector plates or weld in injector bungs (probably best solution) but you will have to make a fuel rail (the 1.9 L-Jet setup uses ancient injectors with hose barbs and hose connections which can be made to work but I'm not sure it is worth the effort). If it were me I would make a fuel rail and use the stock injector plates (which I have done) which is a good solution but a better solution would be weld-in injector bungs and a custom fuel rail. Not really expensive but does take some work. For the L-Jet intake manifold you will have to use/adapt an aftermarket throttle body because the Opel L-Jet TB does not use a Throttle Position Sensor (potentiometer) but rather a Throttle Position Switch which is not compatible with any modern EFI.
I will mine other examples form the forum and reference them here as I find them.

This thread will capture my project/journey to deliver on this conversion and updating of nearly 4 decades of fuel injection technology. We will keep what works well (physical manifold) and update the rest.

Hopefully the performance improves in many ways as restrictions are eliminated.
 

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L-Jetromic fuel injection IS electronic injection, it’s just an analog ECU rather than digital.

True mechanical fuel injection would be Bosch K-Jetronic, or old school Kugelfischer injection.
 
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1975 Opel Fuel injection is not sequential, it fires all 4 injectors at the same time and inject twice per four stroke cycle.
 
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Discussion Starter · #6 · (Edited)
1975 Opel Fuel injection is not sequential, it fires all 4 injectors at the same time and inject twice per four stroke cycle.
Hopefully that can be changed with modern fuel injectors and modern ECU brain. I just don’t know enough yet to understand all of the sensor inputs required for sequential electronic fuel injection. Would sequential EFI require a crank sensor and cam sensor?
 

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Discussion Starter · #7 · (Edited)
So one of the principles during the update is to keep this system is SIMPLICITY. I want to keep it as simple, clean, and compact as possible. That means using 1 part where possible instead of 2 of 3. In the words of Einstein the design should be as simple as possible, but no simpler. Thomas Edison called combination of functionalities task unification.

The first area up for debate is the throttle body. I believe RallyBob identified a certain Nissan throttle body with similar diameter and bolt pattern spacing. Sounds simple, but hard to find the right throttle body diameter and bolt pattern spacing. The good news about this option is that it includes a modern Throttle Position Sensor, which is great and addresses our need for Throttle Position Sensing input into our modern EFI ECU computer.

Here is the RallyBob posting on the subject.

One of the problems with trying to get an aftermarket ECU to work with an Opel fuel injection manifold is the lack of a proper TPS (throttle position sensor) on the throttle body.

I found one possible solution quite easy to implement, by adapting a late model throttle body to the Opel intake manifold. The throttle body I've used is from a 1991-1994 Nissan SR20DE engine (found in the Sentra SE-R and the Infiniti G20). The bolt pattern of the throttle body is exactly the same as an Opel's, but the securing hardware is different. Opel uses 6mm studs to hold the TB in place, while the Nissan TB is held down by 8mm socket cap screws. I simply removed the Opel studs with vise-grips, then drilled the holes out a bit and tapped them to 8mm x 1.25 thread. Now the Nissan TB bolts right up with the stock Nissan bolts. Even though the Nissan TB is 60mm vs. 55mm for the standard Opel part, the intake plenum opening is already large enough and no port matching is required.

The only thing left to consider is the throttle linkage attachment, which has a few possibilities.
Ideally, I would like the throttle body to also include the idle air control capabilities. Any ideas on options that meet this criteria?

the last item that comes to mind to ponder is the throttle linkage. Three options come to mind:
  1. Modify original highly unique Opel GT hard linkage throttle
  2. Switch to a throttle cable for the final connection
  3. Drive by wire (electronically controlled throttle body)
 

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Just Some Dude in Jersey
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Keep in mind that the oem FI was solely focussed on economy and low emissions, with very little consideration of power. When I was configuring the 2.4 motronic FI on my 2.4, we tried out an aftermarket throttle body that was the equivalent size to the larger throttle on a 6 cylinder 3.0 liter Opel FI system. The 2.4 computer was too dumb to handle the much larger air flow, but at about mid-throttle it had rev response that was super fast, like you are trying to achieve. With a more adaptable computer, that could deal with the higher air flow, we could have made it work and gotten a faster rev'ing engine.

So, what I'm saying is: Don't get locked into the stock throttle size. I don't know how one calculates the maximum size throttle that an engine can handle, but going big on the throttle is something to consider. I'm sure there are detriments to going too big or too small.
 

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Discussion Starter · #9 ·
I hunted around for some throttle bodies to repurpose, starting on the Nissan replacement track.
Automotive tire Rectangle Font Auto part Camera accessory

This Item says it has a built in throttle position sensor, built in Idle Air Control circuit and built in throttle position actuator (sounds like drive by wire). But it only seems to have 1 plug. So, my hunch is that the 6 pins actually control those different sensors / functions.

More research required…
 

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I hunted around for some throttle bodies to repurpose, starting on the Nissan replacement track.
View attachment 444674
This Item says it has a built in throttle position sensor, built in Idle Air Control circuit and built in throttle position actuator (sounds like drive by wire). But it only seems to have 1 plug. So, my hunch is that the 6 pins actually control those different sensors / functions.

More research required…
Looks like drive by wire to me....
 

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If it has to be a common plenum FI intake instead of ITBs, why not use a larger cut-off six cylinder 30E intake together with the larger six cylinder C30NE throttle body ? Easiest to do with a C24NE head, but it's also possible to modify the intake flange by welding if used on a 1,9-2,0 liter head.
 

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Just Some Dude in Jersey
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I'm not sure what exact type he got. They were already cut down from 6 to 4 cylinders in Germany/Poland and welded up, so I presume they were from the correct engine to modify GT's.
 

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Discussion Starter · #16 · (Edited)
Ok, so I finally got a good first look at the 75 injection manifold from 1.9 liter Opel today. The bare intake manifold flowed really well on my home made flow bench. In fact it flowed better than any manifold I have tested yet.

I was thinking that I would locate the new modern fuel injectors in the center of each runner. But was surprised with what I saw.

The picture below is looking back up the runner from the head side flange. The hole in the ceiling is where the injector was mounted. The yellow circled area is the protrusion that sticks into the air stream. I spent time last summer machining off similar restrictions when porting my down carburetor manifold last summer.
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And, instead of being centered on the port, the fuel injection slot is off center in the runner. And not just a little bit. The offset of the edge of the injector slot from the wall is 5 mm on the left side and 12 mm on the right side.
Grey Headgear Font Rectangle Gas


So, does anyone know why the hump in the middle? My hunch is that it is there to add metal to the casting for structural support around the center attachment screw for the injector plates. The picture below shows the 3 injector plate mounting screws and the yellow circle represents the approximate hump location.

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But my plan is to weld in the injector bungs, so the mounting holes are not required. If this is the case, my approach would be to grind off the hump and open up the runner so that it has constant cross sectional area. Then I would place the injectors in the center of the air stream.

Does it make sense to center the injectors or am I missing something?
 

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Alot of that port irregularity comes from the way the cores were molded. They were split about 7/16 of an inch from the top of port. But the reason why the injectors are offset ?? Not sure on that one..
 

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I may be wrong but it seems to me that it wouldn’t matter where on the flow perimeter the injector squirts from.
 

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Just Some Dude in Jersey
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The bump might be there to add turbulence near the injector to improve air/fuel mixing or to push the airflow towards the offset injector to improve air/fuel mixing.

The injector offset may be to better aim the spray of fuel in the direction that the air flows through head. The ports in the head aren't a straight shot to the valve/cylinder, they each bend right or left towards the valve.
 

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Discussion Starter · #20 · (Edited)
Ok, so I removed all of the humps near the runner ports with my die grinder, much smoother, consistent cross sectional area now, especially on outside runners.

But, as I am lining up the fuel injector bungs, I am seeing the error of my ways. There is no clear path to machine the angled port to receive the fuel injector bung, since the plenum is in the way.
Grey Sculpture Wood Art Statue


So, here are the options that I am considering to proceed:
  1. Machine holes for the injector bungs from opposite direction (from the inside of the head flange). May require some clever fixturing, as I am not sure I could get it in my mini mill at the proper angle / clearance.
  2. Drill and weld the bungs into a piece of aluminum similar to original design but welded (Rallybob did a prototype of this). Then weld or screw the aluminum plate to the runner arms.
  3. Machine slots from top using a small hand tool (like Dremel tool). Maybe hard to do this consistently across runners.
  4. Cut off some of the angle / length of the runners and weld back together (@scifi guy mentioned this idea)
  5. Cast intake manifold of modified design (see other thread for this approach). Same design intent ad option 4, but cast whole new manifold or just new arms. I have a sketch of this in CAD already and will post it
 
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