Engine/Transmission (1998.5 - 2002) Best Rear Diff. Ratio for 24-valves

[MP in WA]

I have a friend who is about to purchase a 2002 CTD in a 3/4 ton truck. He asked me (12-valve owner) which rear end ratio would yield the best mileage when unladen. I seem to recall reading somewhere (this forum or the TDR magazine) that the 4:10 ratio would actually yield the higher mileage with the 24-valve. Is that correct? This is potentially a new TDR member so please help out. Thanks in advance for your help.

 

[DarrellB]

Boy are you askin for it

You will probable open up a huge can of worms with that question.



I have the 4:10s in my truck and get about 20 to 21 mpg unloaded and about 17 to 19 loaded (depends on how loaded).



I have a Friend with a CTD that has 3:55's and he gets worse mileage but I know of some that get better. I think it depends on what your freind will be doing with the truck. Is he going to drive it unloaded most of the time and then when he does haul something will it be relatively light? If so he probable go with the 3:55's. If he plans on going with bigger tires and hauling a lot of heavy loads then I would go with the 4:10's.



I hate driving a CTD with the 3:55's it just seems like a slug to me but I'm used to power of the 4:10's. I wouldn't trade mine for 3:55's but I wouldn't mind having the new 3:73's that they came out with in 03.



Darrell

 

[SnoKing]

Is he getting an auto?

Lots of towing 4:10's (slow on the freeway)

No towing 3:54's (fast on the freeway)



6 speed

3:54's in a 2500 will handle any load that should be on top, behind, under, in front etc on the 2500.

4:10's got to really what to tow. Maybe in a 3500 with a BIG 5er.





6th gear in the manual is a lower gear ratio than OD in the Auto.



SNOKING

 

[Pit Bull]

See sig. with auto you need the 4. 10, drive 65 and it is right in the engines sweet spot. Now if you like to drive 75 then I would go with the 3. 54, but it will hurt your pulling power with the automatic. It might be 1 mpg difference between the two ratio's.

 

[Arcticat]

Pretty much agree with what has been said. For me, anything over about 70 or so mph with 4. 10's gets annoying real fast. I drove a six speed with 4. 10's for awhile and clutched to shift into non existent seventh gear several times (was used to shifting into fifth on my 5spd with 3. 54 at about the same speed. And when I was out west where the speed limits are 75 in alot of states, I can't imagine not having 3. 54's. I actually wish the overdrive was a little taller when I'm doing 80-85 on the freeway. They are a little slugish on takeoff stock w/auto, but I feel even mild bombing (ez) eliminates the problem.

 

[Bob Wagner]

I am very happy with my set up with 3:54

 

[jwilliams3]

If you would like to drive 125mph on the interstate.

Go with 3. 54



--Justin

 

[StakeMan]

4. 10's with an auto here, and wouldn't have it any other way. I also have 315-75's. 75 mph = 2100 rpm. 17. 5 mpg mixed city, 22. 5 hi-way.

 

[willyslover]

Justin. . have to disconnect one wire to do that speed or you will defuel



I have had both and for my driving style the 3. 54's are the better. . always had the 4. 10's wound out

 

[WadePatton]

Love my 3. 54/6-speed setup. 18+ mpg around town, 19-20 on the highway at 80mph.



Mileage wise he'll just going to be either way.



I only recommend 4. 10's for very regular heavy hauling, real big tires, or mostly off-road use.



And with just a wee tad of bombing 3. 54's will pull anything--without being buzzy at highway speeds.

 

[RustyJC]

We have a 3500 HO/6-speed (see signature) that we use to tow a 13,500 lb 5th wheel (21,180 GCW versus 21,500 GCWR). The 4. 10 is the only way to go IF you're towing this weight. Otherwise, the 3. 54's would be nice for the freeway - 2350 @ 70 MPH gets a little old.



Rusty

 

[Sixspeed]

3. 54's work very well for me

 

[jwilliams3]

Willyslover,

I have not disconnected any wires, and I can do that.



--Justin

 

[andrewkoperdak]

I have 3. 54. Before I bombed with Stage 3 injectors I wished I had gotten the 4. 10. With the new power I can climb anything the interstate can throw at me in cruise at 60 mph between San Diego and Port Angeles WA. That is one statement that says it all ! She will tow faster but CA has a 55 mph trailer law. I generally cruise 70 with no trailer.

 

[Utah Willie]

Best diif ratio for 24 valves

5 speed with 3. 54s on a 3500..... towing 12 to 13k... . works great!... . BUT..... I have a 2 speed aux. transmission (O/D) behind it. I usually tow on the flat freeway in 4th over. In 5th over, unladen, it's 1800 RPM at 72 MPH. Without the aux... ... I'd have to say 4:10s for sure... if you tow a lot.



55 MPH on California's freeways with any vehicle other than a squad car, will elicit a rash of abuse by frustrated drivers stacking up behind you. The trucks I see are most often at four wheeler speed limit.

 

[Posm]

Also, while we are at it we might as well debate what the best hair color for a wife.



There are so many factors to consider. The 3. 54 and the 4. 10 will be in the sweet spot at "normal" driving speeds, albeit one at the top end and the other at the bottom end of the range. The transmissin makes a great deal of difference in the choice. The high gear ratio is . 69 in the auto, . 71 in the six speed and . 73 in the five speed. There is more difference in final raios between a auto and a five speed (6%) than there is between a 3. 54 and the new 3. 73 (5%).

Tire size is also a great deal of differece. There is 5% difference between the stock 245/75/16 tires and the optional 265/75/16 tires. The "tall" tires can add another ten or 15 percent of gear.



If he is going with a manual transmission, stock tires, and will do a lot of light towing, under 15K GCVW, or bob-tailing I would go with the 3. 54. Also, it would be the right choice if he likes to drive 75 or 80 MPH routinly on the interstate.



If he wants an auto, big tires, or will tow near max rating often I would go with the 4. 10s. The six speed does offer enough gears that he could run in 5th while towing 20K loads and still keep his 3. 54s for running empty.



One man's opion. It's worth what it cost you!!



Bryan