[Christ]

Unfortunately, I have to stick a word in here.

I did two mods in the interest of power to my Civic that also increased efficiency to a point where my economy improved noticeably.

#1 MPFI swap. Started with DPFI, and with my (then) driving style, this wasn't working out well. No torque on the bottom of the revs at all, so I was always revving up to keep the car moving. I seldom used 4th or 5th gear. After the MPFI swap, more low-end, so I used the lower gears more.

#2 eBay header. Yep. $32 shipped, and (no scientific data here) about 3MPG increase. Of course, again, I was also driving much differently then than I do now. Also, there was a marked increase in low-end again, header vs OE exhaust. I did not remove the cat or install an open muffler. I had a thrush turbo muffler on the back, in the OE configuration. Later, I installed a fart can, but left the baffle in it. I never noticed a decrease in torque until I removed the baffle.

Both of these are non-conventional mods in the terms of the way we (the majority of people on this site) drive, but if you don't drive like us, they may make a difference for you.

In all honesty, I'd probably do both mods again, except change my transmission to longer gears to accommodate the increase in torque. This is where I wish I'd kept my Civic and the HF transmission that I sold.