Hi gang, thought I'd give the 2-3 people that care an update on how my DIY tuner project is coming along.
I spent a few hours last night fiddling with the IAT sensor, and found adding ~50 degrees of temperature results in ~2 degrees less timing, all else being equal. This is a good thing, but not good enough to run the 12/13psi I'd like to run. I've come to the conclusion that we need to richen up the target AF ratios (big surprise!)
So, this morning I did a little web research and headed off to radio shack to make something more sophisticated. It's been a lot of fun learning exactly how all these little components work, and today I got a lesson in transistors. These are of the NPN variety.
The basic concept is the circuit turns on @ ~5psi and richens the AF ratios up ~1-1.5pt (adjustable) across the board. Later I'll throw the IAT attenuator back to pull out ~2-3 degrees of timing over 5psi, and if all goes well I think I'll be able to run ~12.5psi on 91 octane.
The breadboard I have is pretty big for testing (around 3"x7"), but I think the entire circuit could easily fit in a small key-fob size box. I've also ordered some BMW ECU connectors to make the entire thing plug and play. Once those and my portable wideband setup get in, I'll throw it on the car and do a little more track testing. I might even pony up $65 for a dyno one of these days.
Everything you see on the board plus the ECU connectors comes to a grand total of about $10.