woah wth

[Jackpine]

Here's a list of OEM rear axle codes. You can find the code for your truck on your driver's door sticker.

19 = 3.55 open
H9 = 3.55 LSD
26 = 3.73 open
B6 = 3.73 LSD
27 = 3.31 open
18 = 3.08 open
25 = 4.10 open
B5 = 4.10 LSD

- Jack

[Unleashedford]

there you go, h9 3.55

[Longshot270]

Originally Posted by Unleashedford

there you go, h9 3.55

Yeah, that gear does great on the highway but not so great in the city. How many highway miles are you going through to get that average?

Like Jack mentioned earlier, the gryphon average isn't always correct. Just keep getting your average like you would without the fancy technology. Pencil and paper. That is always more accurate unless your tires are the wrong size from stock. That will throw it off too.

[Unleashedford]

i have 35's on right now, and the mpg went up to 14.1 today but now at 13.7, i think it might be the way i drive i guess?

[Longshot270]

The gryphon average will change quite a bit until you have at least 30-45 minutes of driving. Is the 13-14 city, highway or a mix?

[Unleashedford]

its a mix of both, is that good or bad?

[Longshot270]

Well I'm not an expert in the 5.4s because I only have a 4.6L with the 3.55 LS. Those numbers that you posted are pretty close to the same mileage I get. My daily trip may include 3-9 miles of 55 or so mph on backroads followed by about a mile or two of stop and go city driving that has about 10 lights that prefer to stay red...not to mention multiple railroad crossings but I usually beat the train. That trip will average 13-14 regardless of my driving habits. No joke, driving nice or pedal to the metal its all the same .

How does that compare to your driving?

[JWBFX4]

Originally Posted by Unleashedford

i have 35's on right now, and the mpg went up to 14.1 today but now at 13.7, i think it might be the way i drive i guess?

I dont think you are doing to bad with having 35's on with 3:55's

Heck I have stock tires 3:73's 5.4L and I average between 13.8 and 14.7 with mix driving.

[cody994x4]

unleashedford, im not sure abt mpg's but i know if you were to re-gear you would have alot of restored power. the minimum reccommendation, as far as ive ever heard is at least 3.73's with 35's, 4.10 or 4.56 would be better. you will be able to get going alot easier and put your rpms back around the powerband range. im curious to what your rpms are at say 70mph with the 35ers

interesting how this plays into the mpg equation though, your tires are lowering your rpms thus saving gas...

for economy you might wanna stay where you are but im pretty sure your asking alot out of a smaller ring/pinion.

you might wanna research restored power vs economy if you were to re-gear.

[Jackpine]

Originally Posted by cody994x4

unleashedford, im not sure abt mpg's but i know if you were to re-gear you would have alot of restored power. the minimum reccommendation, as far as ive ever heard is at least 3.73's with 35's, 4.10 or 4.56 would be better. you will be able to get going alot easier and put your rpms back around the powerband range. im curious to what your rpms are at say 70mph with the 35ers

interesting how this plays into the mpg equation though, your tires are lowering your rpms thus saving gas...

for economy you might wanna stay where you are but im pretty sure your asking alot out of a smaller ring/pinion.

you might wanna research restored power vs economy if you were to re-gear.

I've "bolded" the part of your response that is most significant. The lower RPM's CAN save gas, but you've got to get there from a standing start. In his case, the bigger feet make his engine work a lot harder getting it up to speed, due to several causes:

1. A reduced "mechanical advantage" (lower effective gear ratio) due to the larger radius tires.
2. More mass to get spinning from a standstill - Newton's third law still applies.
3. More wind resistance (a minor effect, but still there).

Once at highway speeds, you're still not home free because:

1. The bigger feet weigh more and have more wind resistance - so, more fuel needed to keep them rolling.
2. They probably have more "rolling resistance" (skin friction effect with the road) so it takes more power to keep them moving.
3. Even though the engine RPMs are lower, the torque output of the engine has to be higher due to the reduced mechanical advantage. That torque has to come from somewhere, and it can only be additional fuel per cylinder charge.

So, the whole concept of power vs economy is a very complicated tradeoff. Ford's engineers actually tried to get a good compromise at the plant. It CAN be improved, but I suspect it can much more easily be made worse.

- Jack