Ok, kind of a Tech question. Which gear will offer the better hwy mileage. What is the "feel" difference between the two. What about towing? I often drive between SC and OH, @ 475 miles, sometimes I tow my boat - near 3500lbs.

 

3.55 will be a little better fuel mileage compared to 3.73. The 3.73 will offer a little better take off when towing. There is really not much difference between the two. If you go with 18” wheels then I believe the 3.73 are standard.

 

Negative.... I have the lariat with 18in wheels with 3.55 limited slip.

 

3.55 is better for MPG in most cases. if you got the 18 inch tire option I believe the 3.55 rear and would be too low and possably hurt your gas mileage unless the highways you travel are pretty level. every time you would hit a little incline your transmision would shift out of overdrive. so if you get the 18's or plan on getting bigger tires the 3.73 would be your best bet. if not the 3.55 would be your best bet. if you have alot of hills and grades to go over you might concider the 3.73. just my opinion.

 

In that case, you must have a 4X2 with OPTIONAL 3.55 LS according to a Ford order sheet.

 

Yes I do. I was just stating that what he first said, that 3.73 is standard with 18in is not true.

 

I don't think I have seen one post where a guy with 3.73's said he shoulda ordered the 3.55.

There is only a small difference at 70 mph, around 100 rpm.

 

I don't own both but I would think there would be a bigger difference than that.

 

3.73/3.55 = 1.050 or 5% more.

Tires can make as much or more difference than the gears. Here's a tire/gear calculator.

http://pw1.netcom.com/~sgalaba/mph.htm

 

hey guys thanks. I just wanted to be sure about my order before it was too late to change. Very helpful and nice to know the information you all put out.

 

Just to clear it up…

 

My lariat screw 4x2 has 3.73 ls , and I now have about 1500 miles, I like the low end power and it runs up hills real well, without downshifting, mpg is 16.3 , with a mix of hiway and stop and go driving.

 

It depends on the tires and how you drive. the 373 is a good match for the 17" and 18" wheels. the 355 is a good match for the 255/70/16 tires.

There is more of a difference in gas milage in how you drive, the outside temp, and how well the truck is maintained than the difference between the 373 and 355 on a 4X4 with the 5.4L. The 355 will get better gas mileage at a constant speed with no trailer on the freeway. In stop and go driving the gas milage is the same or advantage to the 373..

The 373 has a more consistant gas milage. The lowest gas milage I ever got was running in 4H when the temp was 10*, towing a small utility trailer with 355 (9mpg), and the highest gas milage was touring down the freeway on a hot summer day (16 mpg). The 3.73 ranged from 12 - 15 consistantly. Tires and wheels were the same, 265/70/17 with Lariat steel chrome rims.

I started with the 373, wanted the 355, got the 355, and now prefer the 373. I don't spend much time on the freeway, and even that is fighting traffic. If I made long commutes I would prefer the 355 with smaller tires.

 

That pretty much sums it up. The difference in fuel economy between the two gear sets under the same driving conditions is almost nothing. There are many more factors that influence fuel consumption that picking the shorter gear will provide other noticeable benefits.

 

Just completed a short trip wiyh my SCrew Fx4 with 373 rear, 18" tires and 300 miles on the odometer. First leg of trip of abput 275 miles on mountainess interstate with speeds between 70-90 mph I averaged 17.4 mpg. Return trip over same interstate with speeds between 70-85 mph averaged 18.7mpg. I was very satisfied with these numbers. Average mpg was calculated the old fashioned way, paper and pencil.