you won't see nearly as much on something well designed as a honda as you will on as old of a design as a flathead. I don't think it'd pay off in the long run for many years. you'd be looking at like .1mpg difference unless there's something malfunctioning in your current system. if you have to replace the system anyway, may as well upgrade.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"