mostly commuter driving - go to work, etc. when we travel, we use the wife's mustang (V6) - it gets way better mpg on the highway.

 

i could live with the 12, if i got 20 on the highway. but 12/16 needs to get fixed. keeping up with traffic isn't the issue, it's having to constantly downshift and hit the gas. the power's there, just not at low RPMs and high gear.

 

sounds right. i got an online calculator, then dug out the actual equations and ran it myself on a spreadsheet. if i could find a torque curve for this engine it would help considerably.
i don't suppose you know the reverse ratio by any chance?

 

3.55 1772.16 RPM
3.73 1862.016
4.1 2046.72
4.56 2276.352


this is what i came up with using the equations i found on the internet; it's for 35" tall tires at 65 mph. looks like a diff of 90 RPM...

 

Joe, I don't know what the problem is with your truck, but my 4.2 has adequate low end torque - when I'm driving around town I'm in 4th at 25 and 5th at 35. If I drive aggressively, my mileage tanks VERY quickly. The best mileage will be keeping it under 2000 rpm. What's the hurry? You might get to work 2 minutes faster.

 

are you up to date on all your maintenance?

 

at the low end, i don't have any problems. it's up in the mid range and higher. it's not about being in a hurry, it's about keeping up with traffic - passing a car, getting on an on ramp, etc. - you don't have to be in a hurry to need to get ahead a little; and this truck won't do it in the midrange (35-50 mph) without a downshift and a lot of gas, which i believe is because the 3.55 axle is too high. I believe if i had the "right" rear ratio, i could get what i want with a "little more" gas and without downshifting, thus keeping the RPM's low.
there's no way i could drive around town at 25/35 and keeping it in 5th at 35 just means i'd have to constantly downshift to keep up with traffic. the only time i'm doing it the way you describe is when traffic is not moving, it's creeping.
typically, when traffic is moving, i'm in 5th at 65-75 and generally around 2100 - 2400 RPM. otherwise, it's traffic lights, stop and go, onramps, offramps, lane changes, etc. I've been recording speed and RPM to try to generate a correlation so i can make a better choice of rear axle ratio.

Question - i have a chance to buy a 4.10 gear set from Ford Racing - does the "Racing" mean it wouldn't be suitable for my kind of driving?

 

No. Ford racing is just the name. They will work fine in your truck.

 

dude..try having 3.08s in that thing...my 04 heritage did. awesome highway mileage and a 0-60 of about 9.5 to 9.6 with intake. got 18.9 combined(70hwy/30city) stock, 19.9 with K&N drop-in and 22-22.5 with K&N intake on same routes.

X2

mine is ok low end but 2000 up is where it has the power. but at about 5k it falls on its face. my 04 heritage didnt have the fall on face thing tho. both 4.2s and 5spds. 04s limiter was 5400, 08s was 5200.

 

i wont go into 4th til 40mph and not in 5th til 45 at the LOWEST. mine makes a weird almost shuttering sound like its really struggling if i go any slower. and i will only do those speeds on level ground or downhill. but to be honest i dont remember my 04 doing the sound at all.

 

I don't think so. Doesn't matter what your axle ratio is once you are moving, if you are in the "right" gear, your RPM's will not really differ much. A lot of gas at a lower RPM doesn't really suck any more gas than less gas at a higher RPM.

If I want, I can easily start in 2nd gear without really slipping the clutch - in fact, when I get lazy I drive around town using only 2nd and 4th, shifting to 5th around 35-40.

 

^ if i skip its from 2nd to 4th or 3rd to 5th. but usually thats when im getting on it and then see a cop or something lol

 

thanks!

 

I suspect I'd kill myself from frustration if i was living with a 3.08, after what I'm experiencing with the 3.55. elsewhere i read about a guy with a 2.73... on the other hand he probably fills up once a year or so...

anyway, before i get into the axle gears I'm having the engine and trans looked at - there are some other issues that may be involved, so I'm having a diagnostic done. I'll keep y'all posted.

anyone know about the torque curve for this thing?
thanks for your time
jg

 

a .25 gear change will result in an rpm change of 300 (to give you an idea of what you're really looking at).

IMHO, you will feel very little difference at any speed or acc.