Vehicle: 1993 Nissan Sentra SE, 1.6 liter, 2 door, 5 speed manual tranny
Aero mods: front airdam, about 4.5 inches above roadway
Engine mods: K&N low restriction air filter, hot air intake system
MPG monitoring: Sound card and MPG.java program on laptop computer.
I finally got the sound card interface calibrated to my satisfaction and discovered some interesting things about how the fuel injection is programmed for this car. At around 60-70 mph, there is an increase in fuel economy at about 75% throttle, peaking at 50-51 mpg at 67 mph. Holding a steady speed at 65 gives about 42 mpg, steady speed at 55 gives about 45 mpg.
This is an ideal situation for pulse and glide operation. I had a long stretch of highway to myself, with a posted speed of 65 mph. I decided to accelerate at about 75% throttle in fifth gear to 69 mph, then coast to 60 mph. I chose those limits because the Colorado State Patrol will rarely give a ticket for 4mph over the limit, and the average speed was 65 mph. With a little practice, I could coast mainly down the slightly rolling hills and through curves, and accelerate uphill and through straight sections.
The mpg during acceleration varied from 41 to 52 mpg, then shot up to 250-300 mpg during coast phase. The average mpg I achieved over a 30 mile stretch was 74.54!
After passing through a town, I had another 30 minute section of 65 mph speeds, but this time I had to use the limits of 65-69 mph, because of following traffic. I decided that if I was speeding slightly, and kept the average speed above 65, the person behind me wouldn't have too much cause to complain. Using these parameters netted an average mileage of 65.2 mpg.
The overall economy of a 186 mile stretch, including 12 miles over an 11,000 foot pass, was 57.5 mpg! That's 6mpg over my best oong trip average so far, and really illustrates the benefits of the P&G technique. It also indicates to me that the fuel injection computer can probably be greatly optimized on this car for economy at highway speeds.
I'm thinking about maybe some O2 sensor spoofing, to see if I can lean the mix at very low throttle openings.
Anyway, I just wanted to post these results. Driving style really trumps any tweaks I have made so far...