Speeduino is made up of two components. The open source ECU software and several open source PCB designs for the ATmega2560 Arduino Mega 2560, ARM M4 Teensy 3.5, etc…
The software currently has support for up to 8 cyl sequential injection or ignition (not both at the same time). This is because of the limitations of the hardware (number of timers and channels) originally used when writing the software (i.e Arduino Mega 2560). It is not a limitation of the software!
Adding 12 cylinder sequential injection support in the software is relatively easy. Its just duplicating a lot of the existing code to support 12 injection events. But you will need more capable hardware.
The Mega2560 is very timer channel limited (i think it only has 12 timer channels). But something like the Teensy 3.5 has 16 channels. You only need 12 channels to run 12 cylinder sequential injection.
Because the speeduino software was written around the Mega2560, it is configured like this;
4 channels for ign, 4 channels for inj, 1 boost, 1 vvt, 1 idle. Using 11 out of the 12 available channels.
In theory you can use 2x Teensy 3.5 and have one dedicated to fuel and one dedicated to ignition. They don’t need to know about each other. They would share the crank and cam position signals and run totally independently. It would be pretty straightforward to do and very cheap. I bet one could build 12 cyl sequential injection and sequential ignition with 2x Teensy 3.5 boards for under $100. Now compare that to the $5k a company like Bosch would want for one of their proprietary systems.
I’d rather have 12 cylinder sequential ignition than sequential injection. So my plan is to add support for 12 cylinder ignition to the Speeduino software, and develop a new PCB with 12x ignition drivers based on the Teensy 3.5. While I’m at it, I could do a PCB with space for 12 injector drivers for future expansion. But this is really just an evenings and weekend type project for me so I think I will first get the car running with something off the shelf like a Megasquirt and then slowly develop my own system.