Highway speed gear 3.07 vs 2.87

[Awesomeness]

asked about pedal cause others with the 290hp and gears are NOT having same losses your reporting.

Yes, they are, it's simply math, and I don't say that to be rude, I mean it very literally - you can't escape a 27% change in gearing and have it be anything close to the same. The 290HP engine (28% increase in HP) and 3.07:1 (27% decrease in gear ratio) roughly cancel each other out.

Maybe they don't notice or care, or maybe they swapped to the 290HP and 3.07:1 gears at roughly the same time and so didn't experience much change all at once? I don't know. But I had my 290HP engine for a couple of years before the gear swap last year, and I find the change in pulling/climbing ability very obviously noticeable (no engine changes between the gear swap). So I experienced the nice change to the increased HP, and then the poor change to the higher gearing.

 

[ramdough]

Yes, they are, it's simply math, and I don't say that to be rude, I mean it very literally - you can't escape a 27% change in gearing and have it be anything close to the same. The 290HP engine (28% increase in HP) and 3.07:1 (27% decrease in gear ratio) roughly cancel each other out.

Maybe they don't notice or care, or maybe they swapped to the 290HP and 3.07:1 gears at roughly the same time and so didn't experience much change all at once? I don't know. But I had my 290HP engine for a couple of years before the gear swap last year, and I find the change in pulling/climbing ability very obviously noticeable (no engine changes between the gear swap). So I experienced the nice change to the increased HP, and then the poor change to the higher gearing.

Awesomeness is in Colorado, he also has bigger “hills” than a lot of us. Maybe people that are having a different experience don’t have the big hills.


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[Third From Texas]

I think at the end of the day you simply have to rely on the math, else much of this is based on perception and differs greatly in various scenarios/environments.

I do find it an interesting topic and I've gone back-and-forth on whether or not to re-gear my M1079A1R. I've no background with this big rigs, but I am familiar with how a gear change in a manual transmission effects my off-road cars. That said, even the C7 seems to be reaching at 60 mph and doesn't climb w/o taking a hit (though not as badly as my other truck with the 3116). Yet I'm from the school of thought here that reducing the load on the engine at such speed would be a good thing.

On the other side, I don't want to lose the low end when off-road. I'm quite happy tooling along at 55-60mph (I come from the days when it was the national speed limit and on trips I saw more of the world than we do at these days doing 80 mph. My end game is to have the habitat built out and be towing a small car hauler with a little Baja car on a lot of trips.

It's a bitch to figure out, no doubt. And every driver/situation will of course vary. I'm on a incredibly tight budget and the cost of re-gearing would involve me borrowing money or putting off large parts of my hab build over time. So I may simply have to make do...

 

[fuzzytoaster]

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.

The math I put in a calculator came out to be this:

Gear Ratio (2:1) Tire Height (in.) Engine RPM Transmission Gear Ratio (7th gear) SPEED
2.87 46" 2600 .78 79.5 mph (Top)
2.87 46" 2100 .78 64.21mph (Cruising)

(the site just eats the formatting on this chart)

Yes, they are, it's simply math, and I don't say that to be rude, I mean it very literally - you can't escape a 27% change in gearing and have it be anything close to the same. The 290HP engine (28% increase in HP) and 3.07:1 (27% decrease in gear ratio) roughly cancel each other out.

Maybe they don't notice or care, or maybe they swapped to the 290HP and 3.07:1 gears at roughly the same time and so didn't experience much change all at once? I don't know. But I had my 290HP engine for a couple of years before the gear swap last year, and I find the change in pulling/climbing ability very obviously noticeable (no engine changes between the gear swap). So I experienced the nice change to the increased HP, and then the poor change to the higher gearing.

I like the insight and the math is..well the math, I've seen your previous posts and they're on point but the situation changes things outside this comparison. Since everyone is not hauling @ss at top speed in 7th gear in these trucks (and I hope not) they should have plenty of torque to take on reasonable highway driving speeds and climbing speeds. Location, altitude, road grade, etc should all be considered in ones plan of use. If you're climbing mountains in your area then gear accordingly.

Your own words were "I'm not sure if I would put 3.07:1 gears in again, but it's not quite bad enough to be worth taking them out either." So that tells me they're good enough for most people in most conditions despite your experiences not matching up with mine, cachgeo's, and others.

Texas, being mostly flat, but not all flat, suits the 2.87 gears as does most of the sunbelt states. Colorado, Utah, etc.. consider the routes and plan accordingly. If towing in those environments then why not deal with the 3.90? Food for thought to anyone reading.

I'm curious to know a head to head comparison of two trucks; one 225 hp stock with 3.90 in 7th and one 290/330 hp with the 3.07/2.87 in 6th climbing a steep hill. I haven't crunched the numbers (and it depends on the engine, truck weight, etc) but for the sake of the question would they be comparable at climbing the hill at the same speed? If the gain in hp is negated by the loss in torque by the gears then simplistically they should ascend the hill at roughly the same rate. If we want to get real we'd need to factor in peak/ideal torque, initial assention speed, and etc which makes the answer "well it depends".

Clearly a lower geared truck climbing a hill from a dead stop will ascend quicker but these trucks should be at sufficient speed (50+ mph) on highway to keep some momentum. Would you take the 3.90 geared truck running 2400 rpm @ 54.01 mph up a hill in 7th or a 2.87 geared truck running 2100 rpm @ 55.65 mph in 6th? I personally would be fine if it downshifted into 6th on a steep hill as it's still going faster than the lower geared truck and I probably would have hit the hill going faster anyway. You will feel the speed slowing of course because you have the speed to give that the stock geared truck doesn't have.

 

[Awesomeness]

Awesomeness is in Colorado, he also has bigger “hills” than a lot of us. Maybe people that are having a different experience don’t have the big hills.

True, though I'm not really talking about taking it into the mountains, on steep continuous grades. Yes, it's slower there, but you don't get the shifting, and associated speeding up/down. I'm talking about rolling hills, like are found in Colorado, Ohio, North Carolina, Georgia, etc., where you have a few hundred foot change in elevation over maybe 1/4-1/2 mile, then it reverses.

The math I put in a calculator came out to be this:

Gear Ratio (2:1) Tire Height (in.) Engine RPM Transmission Gear Ratio (7th gear) SPEED
2.87 46" 2600 .78 79.5 mph (Top)
2.87 46" 2100 .78 64.21mph (Cruising)

(the site just eats the formatting on this chart)

Every truck will be a little different on shift points, but with 2.87:1 gears you probably won't actually be able to cruise at 65MPH. With 3.90:1, my truck shifts into 7th right at 60-62MPH. If things are generally flat-ish, I can then cruise right around 65MPH, with that ~3MPH buffer that I can lose (e.g. going up a slight incline) before it downshifts to 6th. With your calculated 64.21MPH, and turning it into a practical range of maybe 64-67MPH, you're probably going to need to cruise at 70MPH to be low in 7th gear without downshifting too often.

I've seen a lot more eastern states moving to 70MPH as the default speed limit, but there are still a lot of 55MPH states/areas out there. In 55MPH zones, you'll be running high RPM in 6th gear to stay under "10 over", or high RPM in 5th gear to actually do 55MPH.

So once you have enough gearing to get to 65-70MPH comfortably, which would be the non-existent 3.3:1 that I was talking about, too much more may be detrimental if the main reason is low RPM / fuel economy.

 

[jwchameleoncorp]

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.

You put in 307s?

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[Celticlady]

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.

I put the 3.07 in my 1999 LMTV. It has the 3116. I have not changed any engine programing. I have it since march 2020. I am happy with it so far.
Lots of very good info here.

Thanks

 

[Overlanding M1078]

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.

which did you go with, 3.07 or 2.87?

 

[wheelspinner]

The math I put in a calculator came out to be this:

Gear Ratio (2:1) Tire Height (in.) Engine RPM Transmission Gear Ratio (7th gear) SPEED
2.87 46" 2600 .78 79.5 mph (Top)
2.87 46" 2100 .78 64.21mph (Cruising)

(the site just eats the formatting on this chart)




I like the insight and the math is..well the math, I've seen your previous posts and they're on point but the situation changes things outside this comparison. Since everyone is not hauling @ss at top speed in 7th gear in these trucks (and I hope not) they should have plenty of torque to take on reasonable highway driving speeds and climbing speeds. Location, altitude, road grade, etc should all be considered in ones plan of use. If you're climbing mountains in your area then gear accordingly.

Your own words were "I'm not sure if I would put 3.07:1 gears in again, but it's not quite bad enough to be worth taking them out either." So that tells me they're good enough for most people in most conditions despite your experiences not matching up with mine, cachgeo's, and others.

Texas, being mostly flat, but not all flat, suits the 2.87 gears as does most of the sunbelt states. Colorado, Utah, etc.. consider the routes and plan accordingly. If towing in those environments then why not deal with the 3.90? Food for thought to anyone reading.

I'm curious to know a head to head comparison of two trucks; one 225 hp stock with 3.90 in 7th and one 290/330 hp with the 3.07/2.87 in 6th climbing a steep hill. I haven't crunched the numbers (and it depends on the engine, truck weight, etc) but for the sake of the question would they be comparable at climbing the hill at the same speed? If the gain in hp is negated by the loss in torque by the gears then simplistically they should ascend the hill at roughly the same rate. If we want to get real we'd need to factor in peak/ideal torque, initial assention speed, and etc which makes the answer "well it depends".

Clearly a lower geared truck climbing a hill from a dead stop will ascend quicker but these trucks should be at sufficient speed (50+ mph) on highway to keep some momentum. Would you take the 3.90 geared truck running 2400 rpm @ 54.01 mph up a hill in 7th or a 2.87 geared truck running 2100 rpm @ 55.65 mph in 6th? I personally would be fine if it downshifted into 6th on a steep hill as it's still going faster than the lower geared truck and I probably would have hit the hill going faster anyway. You will feel the speed slowing of course because you have the speed to give that the stock geared truck doesn't have.

Well I know on my road here in NC when I had 3:90/225 it would max out at 40-43 usually in 6th but sometimes in 5th depending on headwinds. Now with 3:07/290 it holds 55 easily in 6th on the same hill climb. Anecdotal I know but that’s my experience

 

[BERZERKER888]

to ressurect a old but extremely relevant thread.... the "magical" 3.07 gears...is it the actual ring/pinion components or the entire center chunk from another MV that is installed?..for @$6k (ugh)

 

[Awesomeness]

to ressurect a old but extremely relevant thread.... the "magical" 3.07 gears...is it the actual ring/pinion components or the entire center chunk from another MV that is installed?..for @$6k (ugh)

It's usually the whole center section (but obviously COULD be just the ring and pinion).

 

[Celticlady]

Its used complete center. They were $2500 ea. Don't know if the price has changed. Plus you need to change/ adjust your speedometer.

I would have to dig out my paperwork to be sure. I bought my truck from MME. They did all the work for $1000 plus parts.

my rig will go 65 all day long. Did it driving it home pulling my suburban on a car hauler.

 

[BERZERKER888]

It's usually the whole center section (but obviously COULD be just the ring and pinion).

does the center section come from a LMTV donor vehicle or from another family of MVs?

 

[Awesomeness]

does the center section come from a LMTV donor vehicle or from another family of MVs?

They come from MRAPs. The military was getting rid of MRAPs over the past several years in droves, which have the 3.07:1 gears. The military won't sell a complete armored MRAP, so they cut up the body and sell the rolling chassis and stuff. People bought up tons of the geared center sections cheap (as low as $50/ea... so the legend goes).

I don't think any of the FMTV family ever came with them, but an MRAP is just an FMTV chassis with a different body on it. (True for certain models, anyway.)

 

[BERZERKER888]

and now it's @$6k for 2 drop in center junks....I'm in the wrong line of business..lol

 

[Awesomeness]

and now it's @$6k for 2 drop in center junks....I'm in the wrong line of business..lol

It's easy to look at it like that, but probably not how it works at all. Military vehicle parts are feast or famine... the military often decides to get rid of lots of the same stuff at once, and then there are lots of them cheap on the surplus market. Then, the supply dries up and suddenly the price skyrockets for the few remaining available.

But your sentiment is probably how it starts for a lot of those guys selling stuff. They think, "Hey look! <SOME COMPONENT> I want is up for sale on government auction, for 9 pallets (500 pieces). I'll just buy that and sell the rest." And they do that with things that become coveted and go unwanted, so the same people with $6000 gears probably have pallets full of engine coolant tanks and pintles that don't sell.

 

[Blairg]

An update on mine with 2.87's with 225hp.
Got the rear box mounted. Took the stock bed off ( -2200lbs ) and added the rear box (+4000 lbs) with the only real noticeable difference is how much better it rides. Speeds seem to be the same with the transmission adjusting shift points to accommodate the change. Freeway cruising seems to be happy at 63 mph and with the addition of heat and sound proofing can hold a conversation . I have more things to add so finding the 290hp parts will something in the future to do.

Blair

 

[m37charlie]

I have never driven a FMTV but, I have Unimog U500 camper (similar weight and power). IF 2.87s (5.75s?) are still available, one could add the Marmon-Herrington 1150 TC, evidently designed for the rear of the 3700SP. It has a 2.47 low range, same output yoke locations (except for a few inches of the rear driveshaft, I think) .For better
or worse high range is 1.09, not 1.00.
14.00R20s are ~7% taller than 395s, the net effect would be one would still have comfortable 60mph cruising (top speed is irrelevant, FMTVs and their tires should not be ever driven >60 or 65 at most). And all the crucially important low end and offroad abilitywould be much improved, net crawl speed ~1.95x slower thanOEM military spec. Important if carrying everything including kitchen sink.

MVG-1150 | marmon-herrington

www.marmon-herrington.com

 

[ramdough]

I have never driven a FMTV but, I have Unimog U500 camper (similar weight and power). IF 2.87s (5.75s?) are still available, one could add the Marmon-Herrington 1150 TC, evidently designed for the rear of the 3700SP. It has a 2.47 low range, same output yoke locations (except for a few inches of the rear driveshaft, I think) .For better
or worse high range is 1.09, not 1.00.
14.00R20s are ~7% taller than 395s, the net effect would be one would still have comfortable 60mph cruising (top speed is irrelevant, FMTVs and their tires should not be ever driven >60 or 65 at most). And all the crucially important low end and offroad abilitywould be much improved, net crawl speed ~1.95x slower thanOEM military spec. Important if carrying everything including kitchen sink.

MVG-1150 | marmon-herrington

www.marmon-herrington.com

I am curious what those cost. I bet they are not cheap.


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[coachgeo]

I have never driven a FMTV but, I have Unimog U500 camper (similar weight and power). IF 2.87s (5.75s?) are still available, one could add the Marmon-Herrington 1150 TC, evidently designed for the rear of the 3700SP. It has a 2.47 low range, same output yoke locations (except for a few inches of the rear driveshaft, I think) .For better
or worse high range is 1.09, not 1.00.
14.00R20s are ~7% taller than 395s, the net effect would be one would still have comfortable 60mph cruising (top speed is irrelevant, FMTVs and their tires should not be ever driven >60 or 65 at most). And all the crucially important low end and offroad abilitywould be much improved, net crawl speed ~1.95x slower thanOEM military spec. Important if carrying everything including kitchen sink.

MVG-1150 | marmon-herrington

www.marmon-herrington.com

that would be light years more expensive process,;seems to me ,compared to 2.87's, combination14.0r20 tire and 3.07 (combo results also in approx same ratio as 2.87) or the new gear reduction removal hubs now being sold.