Wow, thanks for all the replies guys! I monitored the thread for a while then forgot about it. Glad to see it was educational for so many people.
I noticed this thread on the front page of the site:
http://ecomodder.com/forum/showthrea...
swap-2779.htm
That's a pretty big ratio change. 21% is amazing -- I wish they made such a thing for my car!
Right now I'm driving a miata which gets pretty bad gas mileage for its size. I suspect this is largely due to the engine being poorly optimized in the low range (intake manifold design and cams), so peak BSFC is at higher RPM and is a lower value there because of higher friction. The car really can't get out of its own way below 3000rpm despite being a couple hundred pounds lighter than the Protege LX and having the same engine.
It is possible to change the final drive ratio, but much taller ones are hard to find and making the speedometer read correctly again may not be possible.
BTW: It turns out the automatic protege had a taller top gear (4th).
-Chris
P.S. Speedo is not affected with changes to individual gear ratios. Final drive changes CAN affect the speedo, but in FWD cars generally do not.