i didnt mean to make it sound like i got huge gains LOL. i get excited over a little gain or improvement like..1/2 mpg is hot to me. in hindsight the spacer was added at the same time i added the k&n & the fitch system. so i cant say exactly which one or combo of any makes a difference.
however i have been trying adding acetone to my gasoline ( 2oz per 10gallons) that seems to have made a difference on economy. its close to 1 1/2 or so it isnt exact . but anything helps.

93 xj stroked 4.2 w/4.0 head avenger supercharged 6.5" long arm 35" buckshots rubicon 44's front & rear