Highway speed gear 3.07 vs 2.87

rockDAWG

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For those who have done this switch, is there any preference between these two? Pros and Cons. How much do you give up on offroad slow crawling speed?

I assume the switch is a direct disassemble and install unlike the traditional ring and pinion install, right?

TIA
 

snowtrac nome

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You have to decide what your preferences for most of your driving is going to be. If you are driving on the interstate and are going to run around 70 mph you are going to need good year mvt tires and alter the ctis to allow for higher tire pressures. I don't normally have to drive faster than 55 the gears in it now work ok I have thought about the 307 gears to drop engine rpm and give me a little more rack travel for climbing hills when on the road, the taller gears would also require a horsepower change. im not certain if I want to pay the fuel penalty for more horse power.
 

Keith Knight

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I did the gear change and it’s one of the best upgrades I’ve done. It’s not because I want to go 70 mph it’s because I want to go 55-60 without the engine screaming at me. After the change with an average speed of 55-60 the interior noise level reduced, I gained almost 2mpg and the shift points are almost perfect with plenty of slow moving with no noticeable difference. BUT.... I have a 2003 LMTV with the cat 3126 and I changed the computer program to the 330 HP at the same time and love it.
 

Suprman

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I have the stock 3116 with higher speed gearing. It put the engine more in its power band. I don’t think I lost any low end. I can be on the highway at 58 and the engine isn’t at 2600rpms anymore. The fan isn’t constantly cycling.
 

fuzzytoaster

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Having installed both gear sets on trucks (and the likely source of the 2.87's mentioned) I can provide some insight... you can't go wrong either way. The loss on the low end power isn't noticeable and provides many perks: better MPG, lower cruising engine RPM, less fan kicking in, and less wear in general. You would have the ability to move out of peoples' way on the highway, stay with the speed of traffic, and over take slow vehicles unlike the stock gearing. These trucks are currently geared so low that either gear set is a vast improvement and puts the power band back to where it's most useful for most drivers.

If you have an A1 model then take the 2.87 gears without question. Sure people will first assume "it has more horsepower" but that's only half the point. The torque band for the 3126 and C7 is better and bigger if you program it right. I put the 3.07 gears in my M1078A1R at the stock 275 hp and it absolutely flies through the gears without hesitation, no loss in power, hit 78 mph with room to climb but this is a controlled test. I reprogrammed it to 370 hp (max for this engine) and the torque is the same but the power band is larger. It took hills and overpasses like a champ but it felt the same as the 275 hp programming. I assume it would shine with a load in tow or in the bed. Having hauled a M989A1 loaded with scrap at 275 hp it didn't notice it behind me.

The 3116 at 290 hp would be fine with either gear set as well. The torque band and hp isn't too far off from the 275 hp of the C7. It would behave similarly but I'm sure a 3126/C7 at 330 hp would outshine it since it's a more powerful engine based on displacement, technology, etc. simply put.

The 3116 at 225 hp would be more well rounded with the 3.07 gears in my opinion unless you are planning for mainly distance highway driving. Low end would be no noticeable change with either set. The 3.07 would give you a little more power to overtake people on the highway but the 2.87 would quiet the kitty-klatter down some at similar speed and give a slight mpg advantage.


tl;dr - You can't go wrong with either. Look at your intentions/plans for the truck and proceed as needed. Swapping the rear chunk is pulling the axle shafts, drop the drive shaft, pull and replace. The front is a little more complicated but in essence the same ordeal.
 

rockDAWG

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Having installed both gear sets on trucks (and the likely source of the 2.87's mentioned) I can provide some insight... you can't go wrong either way. The loss on the low end power isn't noticeable and provides many perks: better MPG, lower cruising engine RPM, less fan kicking in, and less wear in general. You would have the ability to move out of peoples' way on the highway, stay with the speed of traffic, and over take slow vehicles unlike the stock gearing. These trucks are currently geared so low that either gear set is a vast improvement and puts the power band back to where it's most useful for most drivers.

................... etc
Thanks, Fuzzy !!! This is the most valuable input. Thank you for taking the time.

Mine will be a 3116 engine. I have no intention to up its HP but would like to consider it if the cost and complexity are manageable for the weekend mechanics
 

rockDAWG

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You have to decide what your preferences for most of your driving is going to be. If you are driving on the interstate and are going to run around 70 mph you are going to need good year mvt tires and alter the ctis to allow for higher tire pressures. I don't normally have to drive faster than 55 the gears in it now work ok I have thought about the 307 gears to drop engine rpm and give me a little more rack travel for climbing hills when on the road, the taller gears would also require a horsepower change. im not certain if I want to pay the fuel penalty for more horse power.
I don't need to drive at 70 mph, but it is nice to have that option.

If our health holds up, we would like to travel from Alaska to the very tip of Argentina for the next 5 to 6 years. Our goal wants to stay in Alaska and Patagonia for a year or so each. But yet, we have to be realistic and adjust as needed. Needless to say, I need to gain more knowledge about LMTV and plan and adapt accordingly.

Thanks for your input.
 

Blairg

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but I'm sure a 3126/C7 at 330 hp would outshine it since it's a more powerful engine based on displacement, technology, etc. simply put.

The 3116 at 225 hp would be more well rounded with the 3.07 gears in my opinion unless you are planning for mainly distance highway driving. Low end would be no noticeable change with either set. The 3.07 would give you a little more power to overtake people on the highway but the 2.87 would quiet the kitty-klatter down some at similar speed and give a slight mpg advantage.


tl;dr - You can't go wrong with either. Look at your intentions/plans for the truck and proceed as needed. Swapping the rear chunk is pulling the axle shafts, drop the drive shaft, pull and replace. The front is a little more complicated but in essence the same ordeal.
Having just gone though all of these questions and seeing Bret's ad about the 2.87's I decided I better get going with my project and order a set from him. First and foremost, Dealing with Bret was a pleasure. Straight forward, honest and informational regarding what I was buying. It keeps my faith in humanity.

My truck is a stock 1078 w/225hp. My plan is to find a 290 hp turbo and up the power. Nothing crazy. Just reliable (hopefully) and figure out what I plan on doing for a camper on the rear. I look forward to 65mph and lower revs.

Blair
 

rockDAWG

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Having just gone though all of these questions and seeing Bret's ad about the 2.87's I decided I better get going with my project and order a set from him. First and foremost, Dealing with Bret was a pleasure. Straight forward, honest and informational regarding what I was buying. It keeps my faith in humanity.

My truck is a stock 1078 w/225hp. My plan is to find a 290 hp turbo and up the power. Nothing crazy. Just reliable (hopefully) and figure out what I plan on doing for a camper on the rear. I look forward to 65mph and lower revs.

Blair
Hmmm.... it seems that your plan is very much like mine.
1. At 70 mph what rpm do you get with 2.87?
2. Let me know if you find a 290HP turbo.
3. Do you have Bret's contact handy?

Thank you so much.
 

Awesomeness

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Personally, I have the 3.07:1 gears, and they are already too big a change. Yes, you get ~20% higher top speed, but you get 20% less torque off the start or pulling up hills. I would not go to 2.87:1. If I could choose any ratio, I would want something between 3.07:1 and 3.90:1, that would still let me drive 65MPH... like 3.3:1 (just a guess, I didn't calculate that).

Gas mileage when switching from 3.90:1 to 3.07:1 is not 20% change, just FYI. My experience is that it's about 10%, over the ~4000 miles I've driven with the 3.07:1 gears.

EDIT: It's also worth mentioning that I also already have the 290HP engine, out of an M1083, too. So I find it slow, even with the bigger engine.
 
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Blairg

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Personally, I have the 3.07:1 gears, and they are already too big a change. Yes, you get ~20% higher top speed, but you get 20% less torque off the start or pulling up hills. I would not go to 2.87:1. If I could choose any ratio, I would want something between 3.07:1 and 3.90:1, that would still let me drive 65MPH... like 3.3:1 (just a guess, I didn't calculate that).

Gas mileage when switching from 3.90:1 to 3.07:1 is not 20% change, just FYI. My experience is that it's about 10%, over the ~4000 miles I've driven with the 3.07:1 gears.

EDIT: It's also worth mentioning that I also already have the 290HP engine, out of an M1083, too. So I find it slow, even with the bigger engine.
I guess more than anything people will need to look at how they will use their truck. If I needed to use the truck at its max weight capability or was a truck that was going to be used strictly offroad I wouldn't change anything about the gearing.
However, in my case it will have a fairly lightweight camper with a motorcycle on the back. Maybe a small trailer on occasion. Being in Central California means its quite a slog on the slab getting to places and having a relaxed RPM while maintaining 65mph will be nice. WIth 7 gears and being an automatic finding the correct gear won't be difficult.
We shall see...
Blair
 

Awesomeness

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I guess more than anything people will need to look at how they will use their truck. If I needed to use the truck at its max weight capability or was a truck that was going to be used strictly offroad I wouldn't change anything about the gearing.
However, in my case it will have a fairly lightweight camper with a motorcycle on the back. Maybe a small trailer on occasion. Being in Central California means its quite a slog on the slab getting to places and having a relaxed RPM while maintaining 65mph will be nice. WIth 7 gears and being an automatic finding the correct gear won't be difficult.
We shall see...
Blair
Agreed, but even an empty truck is noticeably slower going up hills with the 3.07:1 gears (20%, in fact). Honestly, with thousands of miles on them, offroading with the 3.07:1 gears isn't the problem... it's how annoying their bogging down on every damn hill you encounter on the highway. Shift down, shift up, slowly losing speed while trying to climb the hill, ... ugh.

65MPH sits just after the shift into 7th gear, with the 3.07:1's, so every hill you go up results in a loss of a few MPH, which triggers a downshift into 6th, and that causes a rapid drop in MPH because of where it sits in the power band. Like I said, 3.3-3.5:1 would be better.
 
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