Originally Posted By: urrlord
I used to see Holley water injection units in JC whitney catalogs.I have seen people on the web who built their own kits with an aquarium pump ,washer fluid jug,tubing and a basketball needle.Mounted the needle on the top of the air cleaner housing pointing down the throat of the carb.They reported mpg gains.I thought about making one myself.IIRC You cranked the car and after it reached operating temps you would turn on the injection system.I figured it would be good for a highway or interstate vehicle.You just had to remeber to turn the system off if you had it wired to a continuous power source.
I wonder if you could just use a knock sensor, and have it inject under knock conditions. IIRC the knock sensor is listening to 15kHz (?), and probably have to condition that, then feed to say an LM567 tone detector. Then again, probably need it once vacuum drops below a certain level, so a pressure switch would work better to trigger (probably still need disable switch for cranking).