How Slow is a 6.5 NA HMMWV Really?

jrtoffroad

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Hey Guys,

While I sit here checking my EUC status 5 times a day every day, I can't help but day dream about all my plans for my HMMWV. I've purchased a M1123 with the 6.5L NA engine. My original plan was to immediately swap the diesel out for an LS3 I have, but I've been wondering how bad the 6.5 really is... Maybe I should consider keeping it?

Has anyone ever timed their 6.5 HMMWV 0-60? How bad is it?

And, for anyone who has installed a turbo on their 6.5, how much improvement did you see in acceleration? Was it worth the $, or would you go a different route if you could do it all over again?
 

Andyrv6av8r

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No way I'd spend that kind of money to shave a few seconds off of acceleration times. My 1045A2 is fine by me. I drive it knowing it's intended purpose and fast acceleration from a standstill isn't what it was designed for. Top speed is plenty and comfortable which matters to me.
 

jrtoffroad

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No way I'd spend that kind of money to shave a few seconds off of acceleration times. My 1045A2 is fine by me. I drive it knowing it's intended purpose and fast acceleration from a standstill isn't what it was designed for. Top speed is plenty and comfortable which matters to me.
Thanks for the insight. Hopefully I feel the same way, but my track record is not good. Seems I engine swap and/or supercharge just about everything I drive.
 

Maxjeep1

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I’m waiting also and I’m building it over and over in my mind while looking for parts that I know I want/need. I love the LS and I have one in my CJ project. The only swap that I would consider is the mechanical Cummins. What I love most about Hmmwv is that lack of computers and sensors. I’m not crazy about the 6.5 but I will keep it and make a few mods to get more air in and out with a little xtra fuel. I will also keep the weight down. I love the sound of a diesel. I don’t want to do anything that compromises the water forging ability and I will probably not add as much as a lightbulb. Never been a big fan of hacking up a pristine factory harness. I plan on doing some long trips and I can see the benefits of the LS3 and why everyone is drawn to it. I personally wouldn’t have it if someone paid for it and swapped it out for me.
 

Maxjeep1

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If that's the case, there's no way you're going to be satisfied with the 6.5.
Is it really that big of difference between 23 seconds and 18 seconds 0-60? If I’m going to swap I want a sub 6 seconds and I want to spin all 4 wheels. Probably better off with a Jeep if you are dead set on a swap. I have H2 with 38.5 and 4.88 gears and it runs really good but that being said it probably needs 500hp to make any difference at all. It’s also 7,800 pounds if I remember correctly. I understand it’s not the same but drivetrain and weight is similar I would imagine. Sometimes the best thing to do is nothing. You can do what ever you want but you probably can’t just do engine without transmission and transfer case eventually. I watched videos of LSX Humvee and I see how it snowballs and I’m thinking wow you will never get that money back. He does everything with quality stuff and it’s not cheap.
 

98G

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Is it really that big of difference between 23 seconds and 18 seconds 0-60? If I’m going to swap I want a sub 6 seconds and I want to spin all 4 wheels. Probably better off with a Jeep if you are dead set on a swap. I have H2 with 38.5 and 4.88 gears and it runs really good but that being said it probably needs 500hp to make any difference at all. It’s also 7,800 pounds if I remember correctly. I understand it’s not the same but drivetrain and weight is similar I would imagine. Sometimes the best thing to do is nothing. You can do what ever you want but you probably can’t just do engine without transmission and transfer case eventually. I watched videos of LSX Humvee and I see how it snowballs and I’m thinking wow you will never get that money back. He does everything with quality stuff and it’s not cheap.
These things are slow. About half the seat of the pants power of a modern jeep, which I wouldn't exactly describe as powerful.

Personally, I'm good with that. If I want to accelerate briskly, I use a different vehicle. This isn't the tool for that task.

But if you can't stand a two digit 0-60 time, there's no way you'll be happy with a 6.5 in any incarnation.

Thing is, you can mod it all you like and the end result is going to be a less-reliable-but-still-slow-in-the-scheme-of-things vehicle.

Just my opinion.
 

jrtoffroad

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Is it really that big of difference between 23 seconds and 18 seconds 0-60? If I’m going to swap I want a sub 6 seconds and I want to spin all 4 wheels. Probably better off with a Jeep if you are dead set on a swap. I have H2 with 38.5 and 4.88 gears and it runs really good but that being said it probably needs 500hp to make any difference at all. It’s also 7,800 pounds if I remember correctly. I understand it’s not the same but drivetrain and weight is similar I would imagine. Sometimes the best thing to do is nothing. You can do what ever you want but you probably can’t just do engine without transmission and transfer case eventually. I watched videos of LSX Humvee and I see how it snowballs and I’m thinking wow you will never get that money back. He does everything with quality stuff and it’s not cheap.
I'd say 5 sec 0-60 is a nice gain. ;-)

I actually already have a Jeep CJ7 that I'd put a built AMC 401 in and am now swapping a procharged LS stroker into. I'm not dead set on a swap, but I do think the HMMWV is a great candidate given it already has a 4l80e.

The money shouldn't be too bad since I already have most of the parts and would do the work myself. The time is more of an immediate concern. In addition to trying to finish engine swaps on my CJ and Camaro I'm in the middle of my Ultra4 race season, so that car needs my constant attention.
 

jrtoffroad

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These things are slow. About half the seat of the pants power of a modern jeep, which I wouldn't exactly describe as powerful.

Personally, I'm good with that. If I want to accelerate briskly, I use a different vehicle. This isn't the tool for that task.

But if you can't stand a two digit 0-60 time, there's no way you'll be happy with a 6.5 in any incarnation.

Thing is, you can mod it all you like and the end result is going to be a less-reliable-but-still-slow-in-the-scheme-of-things vehicle.

Just my opinion.
Great input. 6.5 mods are probably not the best choice.

When my CJ had the stock 6cyl I timed the 0-60 time at 23sec. Sounds terrible. But it was still very fun to drive. Yeah, it was more fun later when it had more power, but I still drove it every chance I got. I'm sure the HMMWV will be the same.
 
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Action

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Swapping gears will get you faster acceleration (3.08 ) or higher top speed (2.56), but not both.
Am General tried the gasoline engine briefly and ended it. I guess it didn't work out too well in the H1.
The HMMWVs with the 6.5 turbo are about 190-195 HP, IIRC.
 

MarkM

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I have had my N/A M998 for five years now and it's great for what it is. Sure I'd more power and an extra gear but she's fine now. These were never meant to be speed demons and if you need to get somewhere faster look elsewhere. I try to keep mine as stock as possible. Just my two cents. Mark

1589220296964.jpg
 

jrtoffroad

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I have had my N/A M998 for five years now and it's great for what it is. Sure I'd more power and an extra gear but she's fine now. These were never meant to be speed demons and if you need to get somewhere faster look elsewhere. I try to keep mine as stock as possible. Just my two cents. Mark

View attachment 838563
Awesome M998! Man I can't wait! Assuming I can get the 6.5 fired up, I'm planning to stop in Moab on the way home and spend a couple days out on the trails. When I was in Moab for a race a few months back I wheeled my wife's H3. It actually did really well. It'll be fun to try a couple of the same trails for a comparison.

I want to keep a fairly stock appearance, but originality isn't a big concern of mine. Regardless of what I do with the engine, I plan to make some other tweaks to make mine fit my intended use. Nothing too crazy: 17" wheels, interior tweaks, a rear Detroit locker, skids plates and rocker guards, etc. I actually plan to sell my ram pickup once I get my HMMWV. No, it won't be my only transportation, but I do hope to drive it a lot (of course this all assumes I'm able to get it registered...)
 

Mogman

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The 4 stroke Detroit V-8 engines are ALL dogs, (5.7. 6.2, 6.5, 8.2L) installing a turbo on any of them is just putting lipstick on a pig.
Drop a Dmax/Allison 1000 in it and you will never look back, worth every damn penny!!!
If I had mine when I was a teenager I would still not have my license back!!, damn thing can easily come out from under you if you are not careful and a BLAST to drive!
I am about to bid on another Dmax salvage truck donor for my helmet top!!

Even if you are not interested in going triple digits in your HMMWV the experience at say 65-70 MPH is SOOOOO much more pleasant and relaxing at sub 2K RPM (I am running 1950 at 70 MPH) than at 3.2K PLUS!!

Just my two cents......
 

Mullaney

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The 4 stroke Detroit V-8 engines are ALL dogs, (5.7. 6.2, 6.5, 8.2L) installing a turbo on any of them is just putting lipstick on a pig.
Drop a Dmax/Allison 1000 in it and you will never look back, worth every damn penny!!!
If I had mine when I was a teenager I would still not have my license back!!, damn thing can easily come out from under you if you are not careful and a BLAST to drive!
I am about to bid on another Dmax salvage truck donor for my helmet top!!

Even if you are not interested in going triple digits in your HMMWV the experience at say 65-70 MPH is SOOOOO much more pleasant and relaxing at sub 2K RPM (I am running 1950 at 70 MPH) than at 3.2K PLUS!!

Just my two cents......
.
So, my uneducated and HMMWV deficient brain needs help.

You install this DuraMax into the engine bay on this big ugly (cute?) four wheel buggy.
It runs low RPM and pulls really hard. I have heard that before even in just a plain pickup truck.
Now, what about mating the gears on the axles running 70 mph through that big clunky transmission and transfer case?

I agree with lipstick on a pig for a turbo - but is it possible that the engine upgrade is possibly maybe a cuter pig?

Don't know. Don't have one.
Chances are good that I won't be getting one.

I just need to know. I understand the hotrodding.
Have done the same but it was cars with fat tires on the back :)
 

98G

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So, my uneducated and HMMWV deficient brain needs help.

You install this DuraMax into the engine bay on this big ugly (cute?) four wheel buggy.
It runs low RPM and pulls really hard. I have heard that before even in just a plain pickup truck.
Now, what about mating the gears on the axles running 70 mph through that big clunky transmission and transfer case?

I agree with lipstick on a pig for a turbo - but is it possible that the engine upgrade is possibly maybe a cuter pig?

Don't know. Don't have one.
Chances are good that I won't be getting one.

I just need to know. I understand the hotrodding.
Have done the same but it was cars with fat tires on the back :)
Duramax and Allison (or 4L80). You get an extra gear. Drops cruising RPM to 1700ish.

My opinion, the extra gear is worth more than the extra power.

My other opinion, it's a lot of trouble and expense to go through for not a whole lot of return.

The hmmwv should have had a 4bt from the word go. Or even a 6bt. They had to look long and hard to find a really poor choice to power these things with. Very few choices would be worse than the 6.2. And the 6.5 is just a variation on the theme.
 

Mogman

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Actually the return is astonishing, it becomes a totally different animal altogether and the Allison 1000 has double overdrive (5th and 6th) and there is nothing "clunky" about it,,,but yes it is rather expensive depending on your skill and shop setup.

The 6BT is another alternative but you would still need to mate it with an Allison and the body lift must be greater because the inline is somewhat taller (I did my DuraVee with only a 2" body lift) The electronic shift on the fly transfer case is pretty cool.

I did my conversion for under 10K including the donor truck and re-wiring the truck from tail lights through the headlights and building a custom dash with all microprocessor controlled stepper motor "analog" gauges and GPS speedo.

I can assure everyone, unless you have driven a DuraVee you have no idea what that brings to the table.

Halfway though the project I told myself I would NEVER do THIS again but after my first drive I started looking for a donor truck for my helmet top which is also an A0 which has the 2.65 gears, very important I believe.
IMG_20210501_170253393.jpg
IMG_20210414_173122514.jpg
I got the truck on the road in late April and have over 1700 miles on the conversion so far.
 
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jrtoffroad

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Really cool, and I'm sure it's a blast to drive!

I love the d-max engine, but IF I do an engine swap I'll probably go gas. Having owned stock and modified diesel trucks, unless I'm towing heavy, I prefer the powerband of a healthy gas engine. Now, if the HMMWV came with a D-max, 6bt, or even a powerstroke I wouldn't dare swap it out...

I'm gonna try hard to like the 6.5, but I doubt it will stay in there long.
 

Mogman

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Really cool, and I'm sure it's a blast to drive!

I love the d-max engine, but IF I do an engine swap I'll probably go gas. Having owned stock and modified diesel trucks, unless I'm towing heavy, I prefer the powerband of a healthy gas engine. Now, if the HMMWV came with a D-max, 6bt, or even a powerstroke I wouldn't dare swap it out...

I'm gonna try hard to like the 6.5, but I doubt it will stay in there long.
LS swaps are very popular, basically a bolt in deal so I have been told and they don't mind turning 3000+ RPM all day long!
 

Mogman

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.
So, my uneducated and HMMWV deficient brain needs help.

You install this DuraMax into the engine bay on this big ugly (cute?) four wheel buggy.
It runs low RPM and pulls really hard. I have heard that before even in just a plain pickup truck.
Now, what about mating the gears on the axles running 70 mph through that big clunky transmission and transfer case?

I agree with lipstick on a pig for a turbo - but is it possible that the engine upgrade is possibly maybe a cuter pig?

Don't know. Don't have one.
Chances are good that I won't be getting one.

I just need to know. I understand the hotrodding.
Have done the same but it was cars with fat tires on the back :)
To more accurately answer your question, I have had no issues with the drive train, and believe me I have and will continue to beat it hard, I started with a 435HP tune but have since gone back to the stock 385HP tune because my intercooler is a little small (until I can afford a custom one)

As far as gears,, the 2.56 gears along with the 1.92 reduction at the geared hubs and the 37" tires bring the drive shaft speed almost identical with my other Dmax, same year 08 as the donor drive train. (3.73 gears and stock 17" tires)
In fact I am running the same VSS calculation as my one ton (actually running the one tons stock tune at this time) and when the GPS speedo says 60mph the VSS speed is 63mph pretty damn close.

The thing is most are not old enough to remember when all of us were running around with two and three speed autos turning 3000-3600 RPM at highway speeds all the time before the OD transmissions and diesels started coming out in the 80s.

The only issue I have had is with the Autozone half shafts, the rubber boots are too flexible and at post three digit speeds they grow too much and self destruct on the ball joint nut/stud, not going to be a problem with 99.99% of the HMMWVs out there.
 
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Mullaney

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To more accurately answer your question, I have had no issues with the drive train, and believe me I have and will continue to beat it hard, I started with a 435HP tune but have since gone back to the stock 365HP tune because my intercooler is a little small (until I can afford a custom one)

As far as gears,, the 2.56 gears along with the 1.92 reduction at the geared hubs and the 37" tires bring the drive shaft speed almost identical with my other Dmax, same year 08 as the donor drive train. (3.73 gears and stock 17" tires)
In fact I am running the same VSS calculation as my one ton (actually running the one tons stock tune at this time) and when the GPS speedo says 60mph the VSS speed is 63mph pretty damn close.

The thing is most are not old enough to remember when all of us were running around with two and three speed autos turning 3000-3600 RPM at highway speeds all the time before the OD transmissions and diesels started coming out in the 80s.

The only issue I have had is with the Autozone half shafts, the rubber boots are too flexible and at post three digit speeds they grow too much and self destruct on the ball joint nut/stud, not going to be a problem with 99.99% of the HMMWVs out there.
.
Nice write-up. Thank you.

I have to agree that most folks don't remember the "BO" days. Before Overdrive :cool:
The two and three speed autos when the powerglide was still movin cars down the highway worked just fine.

The explanation definitely helps. I always wondered how in the world anybody was happy and paying 40k and still couldn't get down the road at more than fifty miles an hour. There seems to be choices. They just need to be made intelligently!
 
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