m998a1 mpg

[erasedhammer]

F350 is generally quite a bit heavier than a hmmwv.

My Ram 3500 crosses the scales at just short of 9k empty.

Although the military calls these things a 1 1/4 ton truck, the more realistic comparison is a civvy half ton. Or a Jeep Wrangler JKU.

A quick search yields the following weights -

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Back on the topic of fuel economy, I'm seeing 12-15 out of my plain vanilla M998. State highways at 55mph, some in town, and always a 3min idle before shutdown.

I am still of the opinion that the most valid comparison for the hmmwv is the 4 door wrangler. Similar use profile, similar passenger and cargo room/capacity, virtually identical towing capacity, offroad capabilities, and very similar fuel consumption.

I try not to get hung up on fuel costs. I know guys who shut their turbodiesel equipment off the moment they stop, in order to save a few tablespoons of diesel. The cost of the increased wear on the equipment is far more than the fuel saved....

You guys spending $ to improve fuel efficiency may want to do some math - let's say there's a mod to improve by 2.5mpg, which for simplicity's sake we'll call 20%. Call it a cost of $2k to make this modification. The break even point for the cost of the mod is when you've spent $10k in fuel, which is going to be somewhere around 50,000miles. Now factor in that most mods are a tradeoff of performance somewhere else, and it becomes evident that .......

While I'm rambling on the topic of fuel efficiency, it of course often comes up regarding 5ton trucks. My answer - "I get about 6mpg empty." They usually reply with something close to 20mpg... and then I say something along the lines of " but I get about 6mpg loaded 75,000lbs too. What do you get at that weight?" At which point they don't. Different tools for different jobs.

Most of these things are toys. The appropriate measurement isn't how any miles per gallon of fuel. The appropriate measurement is how much enjoyment per $. Using that metric, any of the MVs are hard to beat.

I assert again that the appropriate comparison is a 4 door wrangler. They're also a lot of fun to drive, occasionally have someone eying it up in the parking lot etc. But the hmmwv is more fun to drive, at similar operating costs, and 1/4 the acquisition cost.

In physical size it's a good comparison to a 4 door Wrangler. But weight capacity is a huge difference. You could load a Wrangler into the back of a Humvee and go off roading.
Especially when you get to soft top m1123, good mileaeg, good speed, decent towing, and can carry 2.5 tons.
I always like to call it a cross between a truck and a Jeep. But really it's in a class of its own

 

[Skrilex]

Agreed! My quest for fuel economy is mainly for range. Not so much economy. I do carry 2 jerry cans in each of my MV's but If I can increase 1 or 2 MPG that could make all the difference between walking and driving after a long day of offroading. I'm happy at 15MPG but I will shoot for better.

I’d be happy with 15. I’m hoping my Cummins swap with 4sp will get me up to 17 but I won’t care if it doesn’t.

Also one factor you may not have considered for range is that the biofuel blends get less mpg than pure diesel. B99 can net a 15-20% loss in economy from what I remember reading. So, even with b20 you may lose 1-2 mpg.

I haven’t looked into the water/meth injection or propane injection but it might be worth a look if you’re already carrying jerry cans. I think they can get a good bit more economy that way.

 

[erasedhammer]

I’d be happy with 15. I’m hoping my Cummins swap with 4sp will get me up to 17 but I won’t care if it doesn’t.

Also one factor you may not have considered for range is that the biofuel blends get less mpg than pure diesel. B99 can net a 15-20% loss in economy from what I remember reading. So, even with b20 you may lose 1-2 mpg.

I haven’t looked into the water/meth injection or propane injection but it might be worth a look if you’re already carrying jerry cans. I think they can get a good bit more economy that way.

I'm getting 17-18 with 6.5 turbo and 4l80. I plan on taking out the run flats to see if I can scrape together anymore savings.

If it was legal I'd say run marine diesel before they switch over, that stuff will get you a couple extra mpg

 

[Skrilex]

I'm getting 17-18 with 6.5 turbo and 4l80. I plan on taking out the run flats to see if I can scrape together anymore savings.

If it was legal I'd say run marine diesel before they switch over, that stuff will get you a couple extra mpg

I don’t think it would be illegal. Here they tax the marine stuff at same rate as road fuels. Now home heating oil, that stuff will get you like 10 extra mpg

if if you’re getting an honest 17-18 I have hope of breaking 20 with the Cummins!

do you have the 2.56 diffs?

 

[erasedhammer]

I don’t think it would be illegal. Here they tax the marine stuff at same rate as road fuels. Now home heating oil, that stuff will get you like 10 extra mpg

if if you’re getting an honest 17-18 I have hope of breaking 20 with the Cummins!

do you have the 2.56 diffs?

2.56 diffs, just recently been averaging 17-18. I did just switch climates and terrain, so no more mountain passes on a daily basis and no more cold weather.

 

[mdainsd]

For a point of reference...My 96 H1 with 7.4L gas gets a dependable 6 city and 8 highway.

But I didn't buy it for milage. I'll get all my money back anyway

I'm pretty happy with the prices H1s are bringing.

 

[Action]

For a point of reference...My 86 H1 with 7.4L gas gets a dependable 6 city and 8 highway.

But I didn't buy it for milage. I'll get all my money back anyway

I'm pretty happy with the prices H1s are bringing.

What is an 86 H1?

 

[mdainsd]

What is an 86 H1?

Sorry s/b 1996 H1

 

[ken]

My engine is new, not even broke in yet. So I'm hoping it will get better. I'm thinking of airing up the tires to max on the sidewall and installing a K&N filter. Who knows maybe 17 is with in reach.

 

[Milcommoguy]

Just a heads-up on blowing up or out. The crappy tires on the units being released from the government. I would be real careful to the tires as to anything and everything, age, date code, sitting flat for years, rot and all the things that go wrong with tires. I have seen some unbelievable junk, NOT road worthy tires on "my new hummwv". Just got it from another planet and can't wait to see what it can dooo. And that's besides all the other parts and pieces that are Hummwv. You (not you, you... owners, just saying) Know what you got?, rebuilt, fresh PM, did it myself (ouch), good to go, got a great deal from the tire king... Then blow and go.

Some parts maybe new, other not so much. A good deal at auction could go real bad, fast. Be safe.

Worry wart rank off. OH... That's a new tire (six years old) that blew last week at 40 mph. Yea, I rode home on it three miles (run flat) but side wall split out, so it was junk anyway.

 

[Skrilex]

My engine is new, not even broke in yet. So I'm hoping it will get better. I'm thinking of airing up the tires to max on the sidewall and installing a K&N filter. Who knows maybe 17 is with in reach.

I decided to air up my tires to max psi to make it easier to roll the dead hmmwv into my shop. Bad idea, the 12 bolt wheels can’t handle the pressure and I blew out several wheel seals.

 

[Action]

I have driven with mine at 50 before with no issues. slantback on 12 bolts.

 

[Milcommoguy]

Several wheel seals? As in more than one wheel or was it the studs or ??. Just for conversation... what tires and rims are you running and what is the age of the tires (date code) How's that K&N going?

 

[Skrilex]

Several wheel seals? As in more than one wheel or was it the studs or ??. Just for conversation... what tires and rims are you running and what is the age of the tires (date code) How's that K&N going?

Yes several wheels leaked down to 25-35 psi, then stopped leaking. I don’t know they dates on the tires but they look good condition. Not weathered or anything.

what k&n?

 

[Hummer Guy]

I know dead thread, but wouldn't a 6L80e or 6L90e be the best overall modification for better MPG? Overall, you get better ratios and have a .67 overdrive. Even though the 4l80e is a good upgrade from the 3 speed, it still burns a lot of fuel at 65-70 big time and the engine still be screaming, not as bad as a TH400, but you're still holding 2,600-2,700 RPMs. I would also say changing the fan system out for a vicious clutch one can be an improvement, and if you really want to go extreme, you can look into a turbo.

 

[TOBASH]

I know dead thread, but wouldn't a 6L80e or 6L90e be the best overall modification for better MPG? Overall, you get better ratios and have a .67 overdrive. Even though the 4l80e is a good upgrade from the 3 speed, it still burns a lot of fuel at 65-70 big time and the engine still be screaming, not as bad as a TH400, but you're still holding 2,600-2,700 RPMs. I would also say changing the fan system out for a vicious clutch one can be an improvement, and if you really want to go extreme, you can look into a turbo.

A Hummer H1 group had a person who tried to install a 6L80E behind a 6.5. He posted that it did not go well. He stated that the 6.5 does not have the ponies to support a six speed tranny. He stated that he was unable to use the sixth gear or cruise at higher speeds. I only read his posts. I was not involved in the swap.

This was posted somewhere on TheHummerNetwork-H1/HMMWV forum threads about three months ago. Tranny was from PHR Phoenix Hummer Repairs IIRC.

Needs lots of customizations and fabricated parts and time according to the OP of that thread. He ultimately pulled the 6L80E out and went back to 4L80E. He then sold the rig and purchased a 2006 H1 Alpha/Duramax IIRC.

 

[Mogman]

I installed a 6l80 in a M998 the at the time had a 6.2L and had no issues running in 6th accept going into a headwind, this was a helmet top that weighed about 8K of course it is pretty flat around here on the coastal plains, it could also be set up to be able to switch to manual shift mode and run in say 5th when needed, the 6L80 unlike the 4L80 is an all clutch to clutch transmission so it cares not what gear it is in.

It does have better ratios than the 4L80 with a substantially lower 1st gear but it did not improve fuel mileage, it may have on a lighter M998 but not on my truck, going to a turbo GEP 6.5L only gained a marginal performance increase but an actual decrease in mileage.

The down side is the trans needs a clocking adapter to bolt to the 218/242 TC case and one is not available, at least at the time so I had to custom build one.
Also the controller will set you back another grand for that project.

If you are interested in a substantial increase in performance and fuel mileage install a Dmax/Allison, otherwise IMHO there is no substantial gain over the 4L80E.

The 90 series transmissions (6L90) have a larger output shaft not compatible with the 218/242 transfer cases.

I had high hopes for the conversion and had a blast doing it but unfortunately there is not much hope for improvement when dealing with the crapfest Detroit engine.

 

[Hummer Guy]

I installed a 6l80 in a M998 the at the time had a 6.2L and had no issues running in 6th accept going into a headwind, this was a helmet top that weighed about 8K of course it is pretty flat around here on the coastal plains, it could also be set up to be able to switch to manual shift mode and run in say 5th when needed, the 6L80 unlike the 4L80 is an all clutch to clutch transmission so it cares not what gear it is in.

It does have better ratios than the 4L80 with a substantially lower 1st gear but it did not improve fuel mileage, it may have on a lighter M998 but not on my truck, going to a turbo GEP 6.5L only gained a marginal performance increase but an actual decrease in mileage.

The down side is the trans needs a clocking adapter to bolt to the 218/242 TC case and one is not available, at least at the time so I had to custom build one.
Also the controller will set you back another grand for that project.

If you are interested in a substantial increase in performance and fuel mileage install a Dmax/Allison, otherwise IMHO there is no substantial gain over the 4L80E.

The 90 series transmissions (6L90) have a larger output shaft not compatible with the 218/242 transfer cases.

I had high hopes for the conversion and had a blast doing it but unfortunately there is not much hope for improvement when dealing with the crapfest Detroit engine.

Interesting, makes me wonder how it would do behind the P400 6.5s, unfortunately they're really rare, but I'm still a huge fan of the 6.5s because of how simple they are compared to the duramax and the size compared to the cummins.

 

[TOBASH]

Interesting, makes me wonder how it would do behind the P400 6.5s, unfortunately they're really rare, but I'm still a huge fan of the 6.5s because of how simple they are compared to the duramax and the size compared to the cummins.

I own one of the last P400. Gonna plop into my Hummer.

 

[Hummer Guy]

I own one of the last P400. Gonna plop into my Hummer.

Does anyone have a part list of what can be done to make our 6.5s the closes to a P400? I know about the forged crankshaft but not sure on everything else