I am about to puchase a 06 SuperCab FX4 with the 6.5 box. I can either get the Limited Slip w/3.73 Axle Ratio or the Limited Slip w/3.55 Axle Ratio what are the pros and cons of each? I would think the 3.55 may result in better MPG around town and on the highway then the 3.73 but maybe I am thinking about this wrong. How much more torque will I feel with the 3.73 over the 3.55. I won't be towing anything with this truck.

Please bare with me I am new to the truck thing I am selling my modified 03 Cobra so I am way out of the truck loop.

Thanks fellas,
MJ

 

You've got it about right. Ive got the 373 and tow very infrequently if ever. It does have nice pickup but I only average around 12-14 MPG and I am not a lead foot. I just got the 373 because if I need the ability it is ready to go.

Good luck with the purchase

 

I thought the FX4 was standard with the 3.73's??? I would stick with the 3.73's...you just never know if you will tow or not...plus the gas mileage is not much different between those two ratios...if you want a vehicle for gas mileage, then don't buy an FX4...they only get 15-18 mpg

 

I would stay with 3.73 . Unless you Know for a fact you will not tow anything. And we never know anything for a FACT. Regardless they are not that much different.

 

3.73

 

If you have a choice, go with the 3.73 ls. I only looked at the F150's that had the 3.73 ls. Had an 04 fx4 scab, 05 lariat screw and now an 06 fx4 scab, all with 3.73 ls. They cruise at 80 mph @2000rpm. You are not worried about gas mileage or why would you be looking at a truck with a 5.4 anyway. Always have gotten 13-15 mpg average, even with intake, catback and xcal2 mods. Never had a 3.55 to compare though, you probably won't really feel a difference, but if you have a choice, and you like the options/color, take the 3.73....

3.73 may come with the towing package, all mine have had this.

 

Maybe '06 has options, but Ford used to only offer 3.73 gear ratios with the FX4.

If you want 3.55s you'd need to buy an XLT or Lariat.

 

The FX4 with stock 18's will cruise about 72-73 @ 2000rpms. These trucks not only come with different ring gears but different tire sizes that can make a big difference.

 

3.73s there is almost no difference in gas at all.They shouldnt even offer 3.55 it should be 3.73s or 4.10s without the heavy duty package.

 

I was in the same boat as you a month ago when shopping for my XLT Scab w/6.5 bed.

I test drove the 3.55 a bunch of times, and the 3.73 a few times.

I made up my mind almost immediately after driving the 3.73; the TINY amount of gas you may save only happens on the highway. Since I do more city driving than highway, there is no way that the savings will be worthwhile for the small loss in oopmh off the line when I'm carrying 1200+ lbs of fresh cut firewood.

(I also immediately swapped up to slightly larger tires, and I can say that it STILL feels better at 1600 rpm than the 3.55 axle with factory tires did)

Like everyone else said, get the 3.73; you won't regret it.

E.

 

If you want MPG dont buy an 5.4L period. The 3:73 is a much better combo with this truck though. You will thank youself later!