4.56 vs 4.88

[Pollarican]

Hey guys,

I know this has been covered time and time again but I am kind of in a novel situation. I have a 1993 I'm building, taking parts from a 1991 I had previously built/ had geared. The 91 had 4.56 front and rear, but the rear are garbage. I just finished building a 410 Cammed 4.0 with a fresh hone/ bearings/ Stainless valves and all wear out parts replaced. I'm torn whether or not to buy new 4.56, and get it back in action the way it was (which seemed like pretty ideal gearing), or to buy 4.88s for the front and rear. The explorer will be my Daily driver, with at least 50% highway driving. I might tow a flatbed trailer that weighs roughly 1500 to move things and collect firewood etc, and give my old Inline 6/C6 E250 a break from insurance. Realistically, If I were to go to the next level with bigger tires, Id probably build a set of axles. I supposed it would be nice to have a set of 37" skinny tires If I could get my hands on them, but I wouldn't use them often offroad in fear of breakage.

It seems if the stock tire size was 29 Inches:

To match 3.73 stock tire performance, I would need a 4.50 gear ratio.
(4.56 R&P)

To match 4.10 stock tire performance, I would need a 4.947 gear ratio. (4.88 R&P)

(While running 35 Inch tires)

Would the 4.56 produce better gas mileage? The power was pretty solid.

I put a built 4.88 8.8 in a friend's Heep, and It was way too much gear to be highway driven - the thing wound out at 65-70 real high rpm. I don't offroad as much as I did when I just built the 1991, so I'm torn on what to do. I know I could work some towing power out of the higher gear, but I will only be doing that a small fraction of the time - not going to be pulling a car or anything.

If It helps, I'm running a M5ODHD trans from an 03 ranger.

 

[ZTraz77]

go 4.56.. my 91 with the m5r1 runs a very safe rpm (~2300) in 5th gear on the highway with 315/75/16 tires and has absolutely no issues, plus it has more than enough power to tow or to let the locker leave a couple of peel marks on the pavement

 

[Pollarican]

Pretty much set on doing that - Your comment was a good confirmation on what I remembered about the RPMs it would run on the freeway - amazing what not having the truck running for more than a year can do to your memory - thanks for the input!

 

[tweakedlogic]

I have 4.56 cause I had planned on 35s, now I like the 33s and want to keep them. At 70 MPH, engine spins @ 3000 RPM. Awful fuel economy. Now when I drive highway, I stay under 60 cause of the better mileage. Now I plan my trips for the scenic route so the speeds are lower and the drive is more enjoyable.

If you know for sure you are going to with 35s and want to retain any thing that resembles normal fuel economy, then go with the 4.56. If you primarily use it off road, go 4.88, but stay off the highway. If you only drive highway, don't tow, and want great mileage, go 4.10.


Edit: thanks snoranger.

 

[snoranger]

I have 3.56 cause I had planned on 35s, now I like the 33s and want to keep them.

You should fix that.


Go with the 4.56s.

 

[Flip4ford]

I have 33's and 4.56's-- very happy-- 70mph @ about 2200-2400 RPM.

 

[Pollarican]

Went ahead and bought a new Ford Racing 4.56 R&P. I really thought I hit the sweet spot of economy and performance when I had my 1991 running. The 1991 had 35 BFG KM2's on it and it was perfect cruising the highway.

Thanks for all the input guys!

P.S. - Anybody see it necessary to replace the Limited slip clutches? I have a whole spare set from the old axle and the new axle currently has limited slip - I figure between them I can get a solid pack of clutches that aren't worn.

 

[XLT99]

[/QUOTE]

P.S. - Anybody see it necessary to replace the Limited slip clutches? I have a whole spare set from the old axle and the new axle currently has limited slip - I figure between them I can get a solid pack of clutches that aren't worn.[/QUOTE]

Mine as well do it while everythings apart so you dont have to tear back into it later

 

[tweakedlogic]

I say rebuild it so you know it's good for a long time. If your going to open it anyway, might as well since the clutch kit is $70.

Get this Limited slip kit, and stack the clutch differently.
Stock stacking: CSSCSSC[X]CSSCSSC (3 clutches/side)
"Performance stacking": CSCSCSC[X]CSCSCSC (4 clutches/side)

You can buy two kits, or I bought the above kit and used the thickest stock pad for the extra. I love it. Locks up nice, gentle around the corners. Very good compromise of manners and performance.

You don't need the friction modifier if you run pure synthetic. Be sure and soak new clutches in the gear oil your are going to use for at least 24 hours, so they will soak into the pads.

 

[Pollarican]

XLT - good point, might as well go all in. Heck, with the money I have in the rest of it this is just peanuts.

Tweaked - thanks for the link! I've read about the alternate stacking, guess I'll try and run that since I'm going to be buying the new clutches.



This is an awesome article on regearing an 8.8:

http://www.angelfire.com/theforce/5ohcpa/cpa5ohtech001.htm

 

[Pollarican]

Found this thread and thought I'd do a followup.

Have been driving the truck for about 2 years since I fully rebuilt it. Ran the alternate LSD clutch stacking - works great! If anyone is considering it and worried about longevity - mine is still functioning perfect 20k miles later. I have the truck up on jackstands yesterday and both wheels engage together perfectly forward and reverse.