I modified a 1995 Ford F-150 with a 4.9 liter six cylinder. The pre-groove mpg was 18. The first tank showed an increase to 23.5 miles per gallon for over a 30% gain in efficiency! That is tremendous for a full-size pick up. At $4 gas it will save the owner about $52 per 1,000 miles.
The truck also shows a definite increase, subjectively, in power through the range of gears.
5 Gas Analysis: Hydrocarbons dropped from 173ppm to 20, NOx from 25 to 0, CO .29 to 0, O2 10.4 to 9.7, and CO2 6.7 to 7.3.
What do you folks think?