3.55s or 3.73s

What are you uys running and wich do you think would be the best with torqshift powerstroke combo. I am sure the 3.55s would be a little better for mileage but not sure how the would be with the auto transmission.

Thanks
Ted

If you have the 20" tires the 3.55 will not give better economy and will be a gutless wonder. The 3.73s are plenty enough with the taller tire. Actually the height difference of the 20" wheels/tires makes the 3.73 act exactly like 3.55 gears with stock sized tires.

If you are only looking at 17 or 18" wheels then the 3.55 won't be too bad to deal with unless you tow at maximum GVWR.

just curious, what would rim size have to do with gearing?

rim size doesnt matter tire diameter does.

I was just curious if anyone had any experience with either setup on an 08. I understand how the ratios are affected by tire size. I guess wheel and tire weight may affect power and mileage also. I just figured that with the power of the 6.4 3.55s would be the way to go. We have a 97 5speed with 3.55s and it will do about anything you need it to. Just keep it out of OD once you get it rolling with a heavy load.

Ted

I don't think you can order a new truck with 3.55s so it would have to be swapped. Assuming 4x4 that means front & rear ring & pinion = not really cheap. A 3.73 to a 3.55 isn't too much diffrent like a 4.10 or 4.56 is to a 3.55 gear. Nice thing about 3.73s too is thaty you can tow alot, run larger tires & still get good MPG.

A 3.55 would.nt be a bad combo considering the 5 auto has a slightly lower first gear, but if you tow I would go with the 3.73 any day. I have driven 3.73 and 4.10 s both and I will take a 3.73 over them all. with the 3.73s if I have to drop to drive I,m not killing the motor like the 4.10 does. You will pull harder from a stop with the 4.10 , but I think your millage is gonna be better with a 3.73 over all with stock hight tires.

Dan

I've heard of a few guys getting 18+ with the 3.55's, as said above the Torque shift tranny does have a lower first gear, so unless this is gonna be tow truck more than a DD, the 3.55's should be just fine.

just curious, what would rim size have to do with gearing?

The rim itself has nothing to do with it but the size of the tire placed on those rims at the factory is a huge factor!

Cat, the 6.4 trucks are available with 3.55s now. Ford went to that option in an attempt to help with the fuel economy complaints everybody has about the 6.4s.

I don't think you can order a new truck with 3.55s so it would have to be swapped. Assuming 4x4 that means front & rear ring & pinion = not really cheap. A 3.73 to a 3.55 isn't too much diffrent like a 4.10 or 4.56 is to a 3.55 gear. Nice thing about 3.73s too is thaty you can tow alot, run larger tires & still get good MPG.

They are coming STOCK with 3.55's. Job 3. No need to order. Its a Ford band-aid to try and get the mileage up.

They are coming STOCK with 3.55's. Job 3. No need to order. Its a Ford band-aid to try and get the mileage up.

hell, with 3.55's and dpf delete i bet these trucks could get close to 25 mpg on the highway. i say go with the 3.55's. plenty enough power, an better mpg's to boot

I didn't know they were coming with 3.55s now, that's great news. In that case I agree no reason 3.55s wouldn't be a good combo for daily driving.

I think with the five speed a 3.55 is a good combo, unless your gonna lift it and run taller tires. I know a guy with a OBS that has 3.55 in it and he likes the way it runs. They never offered a 3.55 in the SD you had 3.73 and 4.10s up till you got into F450's . and you could,nt get a 4.10 unless it had duals.

Dan

This truck was designed for towing and or hauling big loads. The 6.4 is a high revving diesel engine. To take advantage of this the lower 3.73, 4.10 and 4.30 rear gears are offered. Many people who buy the powerstroke tow occasionally with relatively light loads. These people would like the mileage of the 3.55 gear and it will work fine. If you plan to tow over 7000 lbs you might not be happy with a 3.55 gear. You will be shifting in and out of overdrive in hilly terrain. On the flatlands you might be okay.

Thats why you lock it out of OD.

5r110s have a tow haul which enables downshifting but it will not lock the truck out of overdrive, it will jsut postpone it to a higer speed.

The trucks are offered with 355s of 373s, 355s being stock and the 373s being an upgrade now.

I beleive the 20 inch wheel comment was made because the trucks that do with the 20 inch wheels also come with a 33 or 34 inch tire, while the smaller wheels typically are around a 31-32 inch tire.

I dont see an issue with teh 355s, its the same as having a 373 truck with 35 inch tires. Now if you plan larger tires down the road, id stay with the lower gearing.

I know of a guy who bought an 08 F-450 with the 6.4L powerstroke and he's running 4.30 gears on the thing. The 08 replaced a 02??(not sure) F-350 dually with 4.10s but the guy does tow a 30000# skytrack every now and then.

My 6.4 has 3.73s, and auto. This is a CCSB 4x4 on 20's. Interstate at 75 its barely at 2k rpms, It is not a turd at all with a load behind it. Tow haul is its own deal all together IMO. I wouldnt have hesitated to get 3:55s, they just werent offered yet. I'm getting around 16.5 mpg with a high of 17.5. This is w/ dpf still on and a little Diablo tuner. Its comin off, just hadnt got around to it yet.
My obs on the other hand has a 5spd (at least for another couple weeks) with 3:55's and it turns about 2200 at 75-80ish. But its still gettin 18.4mpg, checked it a couple weeks ago, thats with a 66mm turbo and hybrids too.

I have a 373 f350 srw and I would get a 355 in a heart beat. The truck has more than enough power if your pulling. The mileage blows though. Spartan and 355 and it would get ok mpg I think. I agree its a band aid fix but at the same time as long as its a fix who cares.

I went by the local dealership to spec out a 2010 F-350 SRW with a 6.4 and was told that 3.55 is the only option until you go to a DRW. Can anyone tell me if this is right? I just don't think that 3.55's will suit me with the pulling that I do. But of course with the proper tuning I could be wrong;)