High RPM's at highway speeds Focus ZX3
 

Ive got a manual transmission in my focus and could help but notice how high my cars RPM's were when cruising. I read on another focus forum some models had a lower RPM on the highway and netted higher mileage in general.

Right now my car idles high when letting of the gas in the 1500 settling to 750 RPM over the course of 10 seconds or more. im going to attempt to adjust or disable the Idle Air Control Valve.

My current RPM's at about 50mph are in the 2500 range i would think around 2k would be more reasonable. what would it take to change out the gearing (transaxle)? and would i see any benefits to doing so?

I also learned today i can stay in 5th gear all the way down to 30mph with out lugging the engine. it results in good mileage at that speed but i think the car shouldnt hold fifth that low.

Those small-car Ford manuals routinely are short gears. The faster you can get to 5th, the better your MPG. Most folks are "town cruisers," meaning they do the abundance of their driving in low-speed-limit areas. By gearing it so that you can be in 5th at just under 35, you can putz around all day in 5th gear in town.

Once you go out on the highway, the engine just revs up, and up, and up.... :( My 97 Escort would take 5th at 29-31 MPH.

you *might* be able to get a taller 5th gear set (or whole different trans). I got one for my saturn for $20 from u-pull-it. I don't know anything about fords or what cars have what ratios and what interchange.

But it can be a good compromise, 1-4 are sort of "sporty" around town and you wind it out a little bit in 4th getting on the hiway but then spend the bulk of your miles on the hiway in a lower rpm 5th.

I've got about 2700rpm@50mph

My dream scenario would be to find a 6-speed box that fits.

im gonna go look on a focus forum to see what others have done or found. do you think that it would be worth the mod in terms of savings? how would one try to estimate the savings by just an RPM change?

I drive a 6-speed and will shift into 6th at 30mph. The engine does not lug and the RPM is at 1250 at this speed and gear. I'm almost never above 3000rpm either accelerating or cruising.

That is quite high. I thought 3000 RPM @ 70 was terrible in my TSX.

Depends on how much top gear cruising you do. In general, I believe manufacturers focus too much on performance and too little on economy. I would think a taller gear would result in significant savings. I'd like to do it on my 6-speed.

IIRC some 2.3L Foci had a taller differential. Also, this chart full of gear ratios of different Focus transmissions might help you.

Optimal cruise rpms should be 1850-2200.

My 5th gear 4000rpm @70 mph but redline at 8600rpms.