I recently fell down a rabbit hole of car modding videos on YouTube. Most/all the videos I watch involve engine modifications, and there inevitably comes a time where the car gets a new tune on a Dyno in order to realize the potential afforded by the mods.

Tuning a modern car involves tweaking parameters in the engine management system, or engine control unity (ECU). Budget builds often make use of the OEM ECU that originally came with the engine (which may or may be the engine originally installed in the chassis) but the addition of forced induction via a turbo or supercharger to a normally aspirated engine usually calls for an aftermarket ECU.

Aftermarket ECUs offer another advantage for older vehicles; by using existing engine sensors, and perhaps adding a few more, a lot of engine control functions can be consolidated in the ECU, rendering various vacuum controls and mechanical linkages unnecessary. This can help clear space in a crowded engine bay, and also improve reliability, serviceability and, potentially performance, fuel economy and emissions.

From my research, tuning an OEM ECU may involve hundreds of dollars in software and hardware. A modern aftermarket unit suitable for upgrading a four cylinder engine starts at about $850, and one can spend more than twice that for an advanced feature set and the ability to run sequential ignition and fuel injection on a six or eight cylinder engine.

The prices of aftermarket ECUs aren’t outrageous compared to the cost of parts or labor for a big project, but they start looking more substantial if you plan to do most of the work yourself while scavenging parts as cheaply as possible. This got me wondering about whether there was a community of people either developing open source firmware for common OEM ECUs, or perhaps custom hardware.

It didn’t take too much looking to find two active projects with healthy communities around them, Speeduino and rusEFI.

Speeduino has been around since X. In 2017 it was a finalist for the hack a day prize. The author, Josh Stewart started out by using Arduino based hardware to run a lawnmower engine. By now it’s been used to run a variety of engines with 4-8 cylinders. The hardware is based on an Arduino Mega. It adds a robust automotive power supply, protection for the I/O channels and driver circuitry suitable for ignition coils, fuel injectors and other components.

A board capable of sequential fuel injection and ignition on 4 cylinder engines is available assembled for under $200. A unit that is plug-compatible with the ECU on a first generation Miata is available for ~$250, including an external housing.

Interestingly (to me), the Speeduino firmware takes advantage of the Arduino build environment and some libraries. This has enabled people to port the firmware to more capable ARM-based Arduino-like devices, like the Teensy. These ARM based platforms afford the possibility of more advanced peripherals, like CANbus controllers, more memory for data logging, and more headroom, allowing things like unlimited software timers to replace a limited number of hardware timers on the ATMEGA.

I think RusEFI has been around since, at least, 2013. There are already some great hardware options. $270 gets you a unit with a robust waterproof case and someone is gearing up to sell a board capable of running sequential ignition and fuel injection on a V-12 engine.

Both systems (currently?) rely on 3rd-party commercial software for the tuning process, but the software, Tuner Studio, is available for less than $100.

I could do a much longer post, but this post is long enough, so, this is where it ends.