My truck came with the equipped with a 292 cubic inch inline-6 engine, which came with a single barrel carburetor. The trouble was, the carb was jetted to run rich (too much fuel, not enough air), and didn't have an adjustment (it only had an idle adjustment).
So I cobbled together a valve which allowed me to sneak extra air past the carburetor, thinning out the mixture.
description of hack
I used an IAC (idle air control) stepper motor, normally used to regulate idle speed on modern cars with automatic transmissions, and welded together a valve body to house it (I was taking a weekend welding course at ACC at the time, which I highly recommend). Thus, as the stepper motor drove the little pintle in, it shut off the air flow, and as it backed it out, it opened up the air flow.
I controlled it using a "boarduino", which is a breadboard-friendly arduino clone. I had the boarduino read a quadtrature pulse-train from a rotary encoder (sort of like a potentiometer, but it can spin all the way around), and used that to control the stepper motor in the IAC (each click of the rotary encoder translated into one step of the stepper motor).
Additionally, the boarduino sent out a PWM signal to an analog needle gauge, which displayed the relative position of the IAC.
Thus, when I got on the highway, I could lean out my fuel mixture by turning the knob.
Using this method, I was able to increase my fuel economy from about 9 or 10 mpg up to a high of 14.5 mpg. Fun!
- the IAC controller: http://jason.pepas.com/code/iac-controller/iac-controller-0.2.tar.gz
- rotary-encoder demo code: http://jason.pepas.com/code/rotary-encoder-demo/rotary-encoder-demo-0.2.tar.gz
- adafruit.com thread about interfacing with the rotary encoder: http://forums.adafruit.com/viewtopic.php?f=22&t=5417
- adafruit.com thread about the final electronics setup: http://forums.adafruit.com/viewtopic.php?t=5475
- youtube video showing the operation of the IAC: http://www.youtube.com/watch?v=DsW8l6ELwTE
- youtube video showing an IAC close-up: http://www.youtube.com/watch?v=tm58ONGb0lA
- pictures of the valve body build-up: http://jason.pepas.com/photos/iac-valve-body/index.html
Here is a graph of my mileage:
My mileage increased from an average of about 10 mpg to about 12 mpg.
- forum post describing major events on the above graph up until 8/13/2007: http://67-72chevytrucks.com/vboard/showpost.php?p=2307450&postcount=5
I have since gotten rid of this motor and swapped in a Mercedes inline-5 turbo diesel. A new target to hack on!