Per on board systems vehicle placed 8mpg avg. "it does not tell city v/s hiway". I couldnt afford to drive it any longer as fuel hit $4 a gallon.
I found the overdrive in these vehicles slips in even the best of situations.
Typical failure issue, bought a mega viper rebuild system, Tried 2x to get it together rite and then took it to a pro. who found drum pressure seal with lip in not out. set shift and lock up to street and strip to reduce slippage in shifts. installed 3500 stahl converter.
Results 11.5 mpg.
Swapped 8 into 1 pipe, with single 4" flowmaster, result nothing positive as I became amused with the sound now not fuel savings.
Replaced tires and wheels to lighter weight, with lower sidewall height but larger circumfrence and gained 1mpg.
Tried air pressure adjustments but seen no noticable change. Removed water pump and direct driven fan, bought new water pump and bored 3/8" holes in driving face of impeller.
" old circle track car power adder trick". Then installed fan clutch, and also Hole sawn 1.75" into aftermarket junkyard aluminum fan blades.
"also circle track car power adder.
Result 13.8 mpg.
This was as far as ive gotten, Due to my Lemon 02 civic failing on the Hiway.
I will never get another Honda! So for now I have to drive the old Kia that the Civic supposedly replaced.
The fuel mileage increases were multi purpose as Im sure you have guessed, For every fuel economy gain there is an equivellent performance gain, It is my play toy but now I can afford to drive it again.
It has been long due for tune up so that would also probbably net in combination with tire pressure a .5 or so increase.
Water pump fins and fan blades are normally designed for maximum flow.
This vehicle as most do doesnt need it, but to sell a warantied vehicle automakers aproach will always lean to overdone and underpowered unless it is a truck.