[bugeye59]

I was considering using Speeduino for a 1275 A series motor.

My plan is to use a weber style throttle body like this
https://www.aliexpress.us/item/3256802478356243.html

along with this manifold
https://www.aliexpress.us/item/3256802828949850.html

Questions:
1) I did not plan on having Speeduino control spark. I just want to use the standard distributor.
Can I just feed the ignition point signal into Speeduino?
2) Any problems with the siamesed intake ports in this case?
3) What IAC solenoids are folks using for situations like this? I was considering a simple VW/Audi IAC like this
https://www.aliexpress.us/item/2255800062479486.html

Any other suggestions appreciated.

[PSIG]

1) I did not plan on having Speeduino control spark. I just want to use the standard distributor. …
Can I just feed the ignition point signal into Speeduino?

Yes, but you will need to either use a high-voltage signal conditioner on the coil(-) as it spikes 150-450V (tach signal). Or, use a current sensor on the coil(+). Or, if your coil power wire uses a ballast resistor, you can pull signal from coil(+) with a signal conditioner. It is more complicated than just letting the ECM control the timing.

2) Any problems with the siamesed intake ports in this case?

Yes. A single-point log TBI (carb equivalent) is often used for even fuel distribution, and even then is not... even. That was awkward wording. 4 injectors (2 for each runner) can work well. The problem is the firing order versus the Siamese ports, and your manifold and DCOE only uses 1 injector for 2 Siamesed ports that fire back-to-back.

Each cylinder should get its own squirt of fuel, but the firing order means the ports do not evenly alternate intake. It's 1-3-4-2, which makes port1 have to quickly inject twice for 2&1, and then port2 inject twice for 3&4. Multiple squirts doesn't help like usual, as extra squirts would all be sucked in by the first valve to open in each port.

Add to that, while 4 injectors would each only squirt once per-cycle (720°), two injectors would each fire twice only 180° apart. That greatly reduces the flow capacity available for the second squirt in each runner. Yes, it can be solved, but it's part of the issue. I hope this is making some sense.

A-series Siamese head.jpg (165.76 KiB) Viewed 507 times

3) What IAC solenoids are folks using for situations like this? I was considering a simple VW/Audi IAC like this
https://www.aliexpress.us/item/2255800062479486.html

Lots of choices. That IAC is fine.

[bugeye59]

No problem with the distributor signal conditioning. I am very familiar with the proper circuit for this.

What if I were to double the frequency of the distributor pulses going into Speeduino to address the siamesed ports issue?

In other words as part of the signal conditioning I add a small micro that adds an extra pulse in between each distributor pulse.

Granted the rpm readings will be double in the tuning software, etc , but so long as I am aware of this I don't see it being a problem.

It seems mechanically redundant to have to install two injectors for each siamesed port. Not to mention this low cost two injector weber style throttle body is a convenient solution for a lot of siameased A series and B series motors out there.

[bugeye59]

The more I think about this it may be better to weld up a plenum manifold with a single throttle body. But even so, to fit two injectors to each port is still very difficult. There just isn't enough room to fit a fuel rail in that configuration.

[PSIG]

Sounds like you're good for sorting the signals. I would anticipate needing a cycle signal (cam-speed) in order to tell the ECM which cylinder is beginning the sequence. The firing order is common, but the manifold induction is odd. This is why waste-spark ignition can work fine (1&4, 3&2), but 2 injectors with that manifold (1&2, 3&4) don't play nice.

The issue I see is the 2-runner 2-injector setup you are considering, and which cylinders each feeds in firing order. So I'd look at the function of that, relative to the fueling of each cylinder. The resolution (more pulses) does not cure the base issue that the cylinders do not intake evenly from one runner to the other. This leaves two cylinders on one runner and injector that fire sequentially (back-to-back), 180° apart, and then nothing for the other 360°. Look at this, and consider the following:

Injector #1 control, in firing order, on your setup: 2 - 1 - nothing - nothing - 2 - 1 - nothing - nothing ...
Injector #2 control, in firing order, on your setup: 3 -4 - nothing - nothing - 3 - 4 - nothing - nothing ...

We see one injector having to squirt twice in 180°, yet do nothing for the other half of the cycle. If you alternated injectors, Cyl1 would be fine, Cyl3 would be OK, but then Cyl4 is dry. By comparison, 2 injectors per-TB would wired to inject sequentially (Cyl1+2 and Cyl3+4), and why log manifolds, ITBs or port injection can also work with fewer issues. Fuel distribution is the enemy.

ECM options are to inject sequentially on 4 injectors, or alternating on 2, or for every cylinder with 1. Batch-firing 2 injectors on that manifold would feed Cyl2 and Cyl3 with 2x fuel and the others 1x. Again, this is the manifold design pooching options, and if the manifold fed INJ1 to Cyl1 & Cyl4, and INJ2 to Cyl3 & Cyl2 - no issues. But, it doesn't. I hope that helps to show the specific issues.

[jonbill]

I think if you ran sequential fuel and wired channels 1&4 to injector 1 and channels 2&3 to injector 2 you'd have the correct fuelling, wouldn't you?
Obvs would need better than basic distributor for the trigger pattern.
And you'd have to size the injectors so there was never overlap between the two channels per injector.

[bugeye59]

I think if you ran sequential fuel and wired channels 1&4 to injector 1 and channels 2&3 to injector 2 you'd have the correct fuelling, wouldn't you?
Obvs would need better than basic distributor for the trigger pattern.
And you'd have to size the injectors so there was never overlap between the two channels per injector.

Sounds like a good idea jonbill. What does PSIG think? I can run a crank sensor if it gets past the siamesed issue.

Granted I'm trying to make this work for my own situation, but that Sherryberg throttle body in the Weber form factor really opens up EFI conversion for a lot other folks running A and B series 4 cyl motors.

[PSIG]

And you'd have to size the injectors so there was never overlap between the two channels per injector.

That's the trick I mentioned with 180° back-to-back cylinders, and that you only have (720 / 4 *.85) = 153 crank degrees from one injection to the next. That's only 21% of the maximum degrees (time) normally available for the injector to flow enough for one cylinder.

To sidestep this, we could run higher fuel pressure (but dead-time increases, now less than 153°), or use injectors 5x normal size to get all the fuel injected in 1/5th of the time , or other creative option. A 5x giant injector would be difficult to control at light loads such as idle and cruise.

At that point, you then hit injection timing, which we can do to set the end-point of the injections so the first injection ends at the right crank angle before the 2nd valve opens, and the 2nd injection begin as the 1st valve closes. Depending on cam timing, that's even less than 153°. Of course, the end-point changes when running at different speeds and loads (runner volume and velocity). If we were not careful with injection timing, it would be immediately apparent as a rapid change in Lambda for those two cylinders, as one would steal part of the other cylinder's charge (rich), while the other was starved (lean).

At some point in all of this, it begs the question of whether that specific manifold design or number of injectors is due for a reconsideration. It works OK for a carburetor with constant flow, but is a problem with timed injection pulses. Siamese ports can be sensitive and unequal when everything is optimal.

[bugeye59]

Understood PSIG, I was not aware that things were so tight timing wise. Seems like I've got some calculations to do.

What I don't see in your discussion is at what maximum RPM you are basing your conclusions. Maximum rpm matters here as well, Right?

I assume I can play with ardu-sim with my Speeduino on the bench and confirm assumptions using my oscilloscope?

[PSIG]

What I don't see in your discussion is at what maximum RPM you are basing your conclusions. Maximum rpm matters here as well, Right?

Eventually, yes. Not today. Today is recognizing what compromises and limitations the engine/port design, firing order, manifold and number of injectors present - at any speed. Some specific to low-speed, with fine injector control of big injectors, that can flow enough to get the job done at high-speed in < 1/4 cycle.

Compromises. All systems have compromises, and you are choosing yours. Know and understand the choices, if you want a choice. For example; picking two injectors, placed under the blades, for that Siamese port design, with that firing order, has many more compromises. Compromises are inevitable, but when we can, we try to pick smaller ones, or ones easier to overcome.

Eventually, it will hit the next hurdle due to dynamics such as induction timing vs airflow mass and velocity, or fuel lag at injector open and close, or more limitations to injection time-frame, etc. Somewhere in there, it ceases to be practical to find a difficult or unreliable way to do it, and deserves a look at simply doing it an easier or better way with fewer mines in the minefield.

Where that line is to cross is entirely up to you, and I am only attempting to relay principles and concepts that will impede or assist movement forward. If you wish, I can provide a comparison of one option listed earlier against the current option, for informed decisions and possible compromise solutions. I am only hoping to help you discover the hurdles you may face along the way, in order to make your own reasonable decisions that fit you. Your project, your call.