1.) I got the HF gear from a fellow RPR member for I believe $30 (good condition).
2.) My engine turns faster because I have the stock Si transmission from gears 1-4, then add the HF 5th, while I believe you have a stock DX tranny. The only true difference between the Si and DX transmissions for a 1st gen CRX is the final drive ratio, determined by the differential. DX's have a taller FD ratio, knocking each gear down several hundred RPM's, despite the fact tha actual individual gear ratios are the same as the Si. The HF tranny has both a taller FD ratio AND individual gears to give it the long legs it has.
3.) The swap actually wasn't as drastic as I had hoped (I didn't do the math beforehand) and so I later picked up a complete HF tranny to one day swap in to cure this high RPM song bird since I drive 80% highway anyway. BTW, if you go w/ the HF 5th gear, only the fifth gear housing has to come off, not the entire tranny. Just jack up the right side and loosen the 5-6 ten-mm cover bolts to access the 5th gear. Also, keep your assembly in the right order! A HELMS manual also helps, which is also provided on RedPepperRacing.com -- Visit there, ask questions, look around, you'll find plenty of answers. Mak

Additional rolling resistance and/or unsprung weight could have something to do with it...how do you recalibrate a Honda/Acura speedo BTW? Mak

I have an '89 CRX HF (yes, the late body) with the shorter geared HF tranny (yes, there were two types for the HF). In 5th gear mine turns @ 2450RPM. If you get your hands on the taller geared HF that number in 5th gear is more like 2150RPM or so. Yeah, nice!

I didn't change anything mechanically, I just used the mile mile markers on the interstate and compared them to my trip odometer to see how far it was off. I typically see how many mile markers I have to pass before my trip will be 1 mile off. So if it takes exactly 25 mile markers for my trip odometer to be 1 mile behind, I know that my speedometer/odometer is reading 4% too slow and thus my mileage is really 4% greater than was measured with the trip (because I covered 4% more miles than is shown).

Thanks for the info on the 5th gear swap. My current trans already has a little bit of a whine in 1st gear and third gears so I am leaning towards swapping in an HF tranny if I can find one cheap enough.

Wow, everyone seems to have much lower rpms than my car. The 1.0L in my Geo turns at precisely 3000 rpm at 60mph (and naturally 1500 rpm at 30mph).

Metrompg, what's your rpm at 60mph since getting the higher final drive in your blackfly?

That POS Suzuki Sidekick I use also turns at 3,000 rpm at 60 mph. While the EPA rates it at 26 mpg highway, it really gets like 16-18 mpg at that speed.

EPA numbers / methodology?
 

Hmmm... The EPA doesn't live on this planet! I saw on TV (yes, there is still some good info on this box!) last night ... the air quality in the San Jacquine
(sp?) Valley ... in California ... was just awful! Yet, the EPA has been telling us (for years!) our air quality has been improving! Geo. Orwell called this "newspeak"....

The Prius turns 1500ish at 60MPH. Since it is a CVT, that number varies with load.