Diesel - Will i regret regearing to 4.88?

[aevgladitorrubi]

I made a deal to get some yukon 4.88 gears locally. my Sport has 3.73 gears and its not so bad, but since im installing ARB lockers i figured id regear. i just conflicted if i will lose too much mileage since i normally drive at 75. thoughts? 37" patagonias with a 3.5 metalcloak gamechanger. thanks.

Way too high-- 4.56

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[Vtur]

I'm running 410s with 37s and imo it's perfect. Glad that i went with 410s instead of 4.56s

 

[rharr]

Here are some charts to give you an idea of what i am talking about

3.0 EcoD

3.6

The ecoD builts almost peak torque at 1800/2000 rpm and is 350 ft lbs and at 215 ft lbs at idle.

The gasser at 2500 rpm is 220 ft lbs and only at 160 ft lbs just off idle.

The gasser needs taller gears to spin the motor faster at a set speed to get into the peak power. The oil burner doesn't care because it's at peak power just off idle.

 

[M390]

I recommend folks take the time to look at an actual rpm calculator. Take into account actual tire size, vehicle speed, and trans ratios. I plan on running 4.56’s with 35’s (measure 33.5” actually) for a little more grunt towing my camper and it puts my Sport S Ecodiesel a little over 200 rpm’s higher than it was in stock configuration at 70 mph. On 245/75/17 tires that measured 30.5” in real life I was churning not quite 1850 rpm’s at 70. On 35’s and 4.56 gears it calculates out to 2040 rpm’s. I see no issue whatsoever with that. The 3.0 V6 Ecodiesel can rev a little comparably, it’s not a 96 Cummins…

 

[rharr]

Here is a quick calc using the ecod ruby as the example. First column of Data is all stock, second column is 35's with 4.10.

The 35's with 4.10 will spin the motor 79 rpms faster at 70 mph in 7th then stock.

Translation you are now at 365 ft lb of of torque at 70 mph, where stock was at 358ish ft lbs at 70 mph. Using 7th gear as the reference gear.

You gained 7 extra ft lbs going to the road at the expense of a little more rpm.

I used the dyno chart above for the torque references.

35's and 4.56's will bump the rpms to 333 rpms over stock at 70 mph and put you at about max torque of 370 in 7th at 2513 rpms.

With the ecoD the changes aren't very big. But if you did the same exercise using the gas motor and it's power curve the ft lb gain would be more since it's curve is gradually increasing and not a flat table like the ecoD.

A gasser will jump from 180 ft lbs at 2396 rpms to 220 ft lbs at 2689 rpms in 7th gear at 70mph when switching from stock 33/4.10's to 35/4.88's. A 40 ft lb increase, which will be noticed by the old butt dyno.

 

[M390]

I myself would choose 4.88’s for 37’s for what it’s worth. I pull a camper occasionally though.

 

[BEERviper]

I have pulled a 32' camper weighing in at 6,250 lbs dry with my ecoDiesel on 37's and stock 3.73:1 gears and it pulled like I expected it to ... most excellently!

The kicker when not towing is it will still hit 8th gear at 59mph on flat roads and hums on the highway at 78mph in 8th gear with minimal downshifts.

IMHO, unless you get the gears cheap and can do the work yourself you're just throwing money away unless you are towing heavy every week (in which case you may have bought the wrong vehicle).

 

[djthumper]

This is interesting, I was looking at things for my Sport D trying to figure things out. With the stock tires I was getting about 27 MPG on my 70 mile round trip commute. I put on some Rubicon 33” take offs and my mileage went down to 24.9. I am not sure if I just want to do 35s or 37s and I do tow periodically about 3 hours away.

 

[M390]

I have pulled a 32' camper weighing in at 6,250 lbs dry with my ecoDiesel on 37's and stock 3.73:1 gears and it pulled like I expected it to ... most excellently!

The kicker when not towing is it will still hit 8th gear at 59mph on flat roads and hums on the highway at 78mph in 8th gear with minimal downshifts.

IMHO, unless you get the gears cheap and can do the work yourself you're just throwing money away unless you are towing heavy every week (in which case you may have bought the wrong vehicle).

With all due, I disagree. Worthwhile mods are definitely eye of the beholder.
That said ARB’s were goin in anyway so why not I figured on the ring and pinions? I have installed quite a few sets though. The labor aspect definitely isn’t cheap no doubt.

 

[M390]

This is interesting, I was looking at things for my Sport D trying to figure things out. With the stock tires I was getting about 27 MPG on my 70 mile round trip commute. I put on some Rubicon 33” take offs and my mileage went down to 24.9. I am not sure if I just want to do 35s or 37s and I do tow periodically about 3 hours away.

Similar deal here. I went from stock 275/45/17’s to 35’s and mileage went from 28-29 to 20 on highway. I hope to gain a little back on MPGs going from 3.73‘s to 4.56’s with my Yokohama 35’s. I have no illusions that I’ll get a lot back though.
Fighting weight, leverage, and aerodynamics that weren’t there before.
It will put the engine in a much closer to stock rev range though.
Hoping to see a little bit better efficiency.

 

[Deleted member 47279]

This is interesting, I was looking at things for my Sport D trying to figure things out. With the stock tires I was getting about 27 MPG on my 70 mile round trip commute. I put on some Rubicon 33” take offs and my mileage went down to 24.9. I am not sure if I just want to do 35s or 37s and I do tow periodically about 3 hours away.

i went from 28 mpg on stock 31s, then 24 on 33, now im 18 with 37s. but i do drive like i stole it and i have a banks derringer.

 

[woffman5]

i went from 28 mpg on stock 31s, then 24 on 33, now im 18 with 37s. but i do drive like i stole it and i have a banks derringer.

Similar here going to 37s on stock 3.73 gears, and I drive like an a**hole as well!

 

[cotnballs2000]

4.10s with 37s will get you back to stock RPM vs MPH. You diesel will have no problem moving those tires and will not hurt your MPG as much.

 

[M390]

4.10s with 37s will get you back to stock RPM vs MPH. You diesel will have no problem moving those tires and will not hurt your MPG as much.

4.10’s aren’t worth the effort. You’re gonna be 200ish rpms lower than stock with 4.10’s and 37’s vs 3.73‘s and 31’s. Borderline lugging the motor. Efficiency will go down I’m betting. Minimum 4.56‘s for 37’s, 4.88’s are better…

 

[Chance575]

I have a set of 488 and Eaton lockers on the bench for my diesel. I went with the 488 to tow and better low end. I don’t travel on the highway much so they suit me just fine. Also if I move up the 39 or 40s from 37s the jump won’t be as bad. I’m just waiting on good weather so I can go back to DD my corvette and start my install

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