I purchased my '97 HX with an SI trans in it. My MPG was pretty low for what I expected. I finally had some free lift time so my buddy and I swapped the stock trans back in (It was included separate with the car):
I've been logging the fuel since day 1. It's easy to tell the before/after of the trans swap per my log:
Currently running 10w30 in the trans to clean it out (some minor debris looked to be in there). I have 2 quarts of Honda MTF that I'll be putting in once I drain this motor oil out.
I'm also planning on doing the grille blocks, raising the car up (Coil overs are too low), then doing an air dam, rear bumper cover underneath, cleaning the EGR system, and some other basic modifications.