355's or 373's

[SNOWNUTZ]

Just totalled my 07 350 lariat outlaw and looking for a new 08. I believe 355's and 373's are bolth availablein the 6.4. I pull a 26' enclosed snowmobile trailer and a 28' car trailer. I pull a trailer probably 20-30% of the time. I'm looking at a 250 or 350 and what I have been hearing on the somewhat poor mileage I was wondering if anyone knows from experience which would be best. Any info would be helpful becauseI know sometimes while pulling the 355's can get worse mileage than the 373's.

This probaly should be under the mileage post but I'm affraid it will be lost in all the pages.

[jayhirsch]

I think it would be hard to measure difference between 3:55's and 3:73's. On a flat road, 55-60 mph...no load...the 3:55's should get better mileage. The more weight you pile on..plus some hills etc...the difference will become impossible to measure...and you are right..at some point 3:55's could be worse...but not much worse. If you like to cruise at 80 mph, empty...I would go 3.55's!

[DirtFarmer]

Most folks disagree with me, but I prefer the 3.55s.

When I'm towing a heavy load, I like to run maybe 62 or 63 mph. At that speed, 3.73's have you running higher rpm than necessary in straight gear and too low rpm in OD.

4.10's would put you in a good rpm in OD but of course are more gear than necessary when lightly loaded.

3.55's allow for a tolerable rpm in straigh gear when towing heavy plus give a nice low rpm OD when lightly loaded. 3.55's have always been my favorite for that reason. This is especially true with the 6 speed stick. It provides enough gears that OD can be set aside for light running only.

[Naztruk]

I just ordered a F350 FX4 with the 6.4 & auto transmission. I was told that the 3.55 was NOT available and ordered the 3.73 limited slip for $50 more. What gives & who has the correct answer?

[SmokeyWren]

Originally Posted by Naztruk

I just ordered a F350 FX4 with the 6.4 & auto transmission. I was told that the 3.55 was NOT available and ordered the 3.73 limited slip for $50 more. What gives & who has the correct answer?

If by "just ordered" you mean since March 1, and assuming the standard 18" wheels, then your dealerperson did you dirt. Effective March 1, on an F-350 SRW PSD with FX4 trim, automatic tranny, and 18" wheels , 3.55 limited slip is standard and 3.73 limited slip is optional.

However, if you ordered 20" wheels, then 3.73 LS is the only ratio available on any F-350 SRW PSD, regardless of trim level.

Before March 1, different rules applied.

But all is not lost. If you ordered 18" wheels and you really want the 3.55 gears, then get back with your dealerperson and demand that he immediately process a "change order" and change your axle code from X3L (3.73 LS) to X3J (3.55 LS).

What's the difference? 4.8 percent, which is about 100 RPM at interstate cruising speed. If you cruise at 2,000 RPM with 3.73 gears, then you'll make the same speed at about 1,900 RPM with 3.55 gears.

[rossi]

Smokey and all...
For those that will see many hours on the interstate and would like to order the 3.55 l/s and then put on after market 20" wheels with 33 or 35 rubber, what effect will this have on the vehicle. Slower take off I assume, would the wheel and tires negate any gains in mpg? Would it be better to stick with the 3.73?

Thank you all!

[ClayHenry]

Originally Posted by rossi

Smokey and all...
For those that will see many hours on the interstate and would like to order the 3.55 l/s and then put on after market 20" wheels with 33 or 35 rubber, what effect will this have on the vehicle. Slower take off I assume, would the wheel and tires negate any gains in mpg? Would it be better to stick with the 3.73?

Thank you all!

There is not a real big difference in the 18" & 20" wheels put some 285/70/18 tires on its almost the same size as the 20" wheels. My 06 had 20" wheels with an 18" spare. I don't think you will notice any difference in milage or take off power.
Tire Size Calculator - tire & wheel plus sizing

[Smokewagun]

Originally Posted by ClayHenry

There is not a real big difference in the 18" & 20" wheels put some 285/70/18 tires on its almost the same size as the 20" wheels. My 06 had 20" wheels with an 18" spare. I don't think you will notice any difference in milage or take off power.
Tire Size Calculator - tire & wheel plus sizing

I notice a definite difference between by fathers 3.73 with factory 18's and my 3.73 with factory 20's. Out of the hole, I think the 20's are a dog. That's without Innovative's help, though. I think the 3.55's will only compount the problem, thus the reason Ford won't build a 3.55 with the 20's. Factory 20's are over 1-1/2" taller than the 18's, if I recall correctly.

[MrSlug]

I moved from 3.73's in my Dodge 2500 to 4.30's in my F350 DRW. Take off and hill climbing power is impressive with 4.30s but the RPMs are quite a bit higher at freeway speed (compared to my old 5.9).

Still love this F350 though.