Speeduino (and a little rusefi)

Matt is right - rusEfi board is more expensive because it has much more on the board. You can assemble the smaller rusEfi board - Frankenstein - for about $100 - but it would not have all the cool stuff Frankenso board has.

the v8 guy is right - MS has waaaaaaaaaaaay more people using it. I think both speeduino and rusEfi are targeting either true open source maniacs or software developers. i could be wrong.

FreeEMS is weird, I believe they've stopped publishing updates and went into some drama mode? 

https://www.youtube.com/watch?v=3xz66oR95F8

There are a bunch of different commercial offerings that tap into stock ECUs, which you can then control with something like TunerProRT.  I have been using that software on a Ford 5.0 (foxbody) ecu, and I enjoy it.  Hardware costs might not be much less that the MS platform -- but I didn't have to rewire the car.  And I knew if I couldn't get it to work, I could just take it off and let the stock system go back on line.

I am the guy with a running ls on speeduino. The speeduino is a good option if you really want to understand how Efi works down to the sensor and signals. It has been a great learning experience that still teaches me new things all the time. The car runs but have not had time to Finnish working all the bugs out. I knew very little about electronics and nothing about tuning. I am still trying to learn tuning. V8 can be semi sequential instead of batch fire. Also since i soldered the components to the board and made my own harnesses from a old cut up stock harnes it only cost me 150 with case total. New things are also being added all the time.

In reply to JBasham :

Thanks, I have a new rabbit hole to fall into now that I googled and saw OBD1 GM mentioned on the website.