6.5L Diesel Repair, Replace or Modify/Upgrade with Duramax/Cummins/Other

[VAMCDOC]

As of now my 1991 HMMWV is in need a new/different 6.5L turbo/nonturbo naturally aspirated diesel. Any suggestions or recommendations of who I should go with for an engine manufacturer/supplier that can get a quality reliable/durable replacement for my HWWMV in South Florida? Should I go with a remanufactured or New 6.5L engine? Obviously it will cost $$$$$ to modify the HMMWV to take a Duramax or Cummins. Anyone know of anyone other than Predator who does this? HMMWV is currently located in South Florida too so if anyone has recommendations on a diesel engine mechanic too that be great as well. Much obliged for the help

 

[patracy]

Some things to consider about the duramax and cummins is the drivetrain behind it. You're going to need to upgrade the transmission at least. Then you need to consider the half shafts. Then with the cummins, you're going to need a body lift to clear it. I'm uncertain about the duramax needing any additional clearance. In the case of the duramax, the easiest fit would be a 4L80e, but a allison would be nice. If I were to go with a cummins, I'd use a 47RH transmission. Of course I'd build any transmission behind them.

Easiest solution is to put a 6.5 back in place. You could also consider a civy 6.5 engine and swap over your oil pan/accessories/exc. to it. (NA motor) But to use a turbo civy engine, you'll need to find a van motor. (Also if you're talking a newer model civy engine, you'd need to swap IPs as well) There's a few vendors here that would have a replacement engine though.

 

[Retiredwarhorses]

It really all comes down to one thing...money. How much money do you want to spend...that will tell you your options.

 

[NovacaineFix]

The Duramax would be good but one thing that many overlook is the fact that these engines are fully electronic and computer controlled, same with the Allison tranny.
If you want to take the task of retrofitting your electrical to accommodate a more modern powerplant, it can be done, but like Retiredwarhorses said, how much money do you feel comfortable in spending?


Not downplaying the Duramax or newer Cummins, they are very nice and provide much more power than the 6.2/6.5/6.5 turbo, but at a cost.
There are always fitting issues when retrofitting different components into an older chassis/body, they can be a PITA, or it may be just a simple parts swap or mod. Your tolerance and bank account are the only things that will tell you no.

Now this is not a MV, but this is a video of a guy who put a Detroit Diesel 435T into a older Ford flatbed truck, just an idea of what you similarly "could" expect if swapping with a newer more modern powerplant.

If you take it on, document everything you can, would love to see the pics and story.

https://www.youtube.com/watch?v=TwxH44bimjQ

 

[DatGuyC]

Good thread about a cummins conversion.

http://www.steelsoldiers.com/showthread.php?66350-New-Cummins-HMMWV-project-in-the-works!

I myself have a cummins 12v sitting in the garage thats just about done. I'm putting a mildly built 47rh behind it with a 242 t-case.

 

[donquijote]

I am interested in doing the same thing as the poster on my 1987 M998 with the 6.5. I looked at all the engines that were made for humvee's and would like to upgrade to one of these:

• 6.5 L turbo GM Diesel V8/GM 4L80-E 4-speed
  or
• 6.6 L turbo Duramax LLY V8 turbo Diesel/Allison 1000 5-speed (model year 2006)

I will swap the tranny also. If i were to call GM and get a crate duramax w/ allison are these direct drop in replacements, or will some modification be required for either of these engines or transmissions? I don't mind going with the 4speed if that is considerably easier to install. I have extensive wiring experience from years of IT work, so i'm confident in my skills. Budget is not an issue, I would just like to work with the most efficient setup. Thanks for any input!

 

[overlordofmars]

I would stick with the 6.5. There are a lot of " General Products " 6.5 engines in the crate available with the updated optimizer heads. I think a company named Meltron Industries in New Jersey lost their contract with the Federal Government and are sitting on a pile of these engines. I know a lot of people love to rip out and replace, but there goes the standardization in the hummer design . There also goes the minimal use of electronic garbage. I am driving a 1994 6.5 with the PMD and all that electronic stuff that goes screwey and leaves you stranded. I allready relocated the PMD and replaced the sensors due to that fact. I think, the less electronics the better.

 

[donquijote]

Totally agree with your synopsis and keeping it simple with minimal electronics. That is one thing i love about the humvee, the simplicity. I more or less wanted to go a little faster (70mph) on the interstate and have a little more overall power. OK, so i have the 6.5 that it was upgraded to in 1990s. Do you have a list of recommended modifications to squeeze all available efficiency and power out of these particular engines? I was going to have it rebuilt if sticking with the original engine it was upgraded to.

 

[overlordofmars]

Optimizer 6.5 upgrades, including the aftermarket turbo. A 700R4 transmission from TCI, set up for towing/ diesel applications. Secondary transmission cooler, the big one. OR try to find a General Products engine. Here is whats from their website .

Created by General Engine Products, a subsidiary of AM General, the Optimizer 6500 is a high-performance, American-made engine that greatly improved on the power and reliability of the General Motors engine originally offered in production Hummer® H1s. The Optimizer incorporates many improvements in design, technology, and metallurgy to redefine the abilities of the original engine.

GEPP takes the power and reliability of this fine engine and steps it up to the next level, adding a custom turbo charger and other performance enhancements to create the finest engine available for critical military, racing, and extreme off-road uses. GEPP's engines have been used by virtually every H1 off-road race team and by many military groups worldwide.


I have A 6.5 General Products 6.5 in my 1987 Federal Suburban. I replaced the dead 6.2 with the 6.5 , then put in a heavy duty 700R4 from TCI. Now I got luckly , I got my engine by accident. I bought a M1009 that a fire company had and in the back sitting on a pallet was the 6.5. Apparently they thought the engine had a knock and was bad and got the engine from federal surplus to fix it but never did. Turned out their 6.2 only had a cracked fly wheel. So I had a new clean 6.5 sitting here. I like it, its got some pep over the older GM version of the 6.5

 

[donquijote]

Awesome. I will look into going that route.

 

[VAMCDOC]

Agree. My GM 6.5L engine apparently overheated at some point and had a warped piston and the cylinder in #6 is not cracked but "corroded" and needs to be machined out with a new piston put in. A lot of work or a new block or with a rebuild. The GM 6.5L diesels are loaded with defects and problems apparently. The GEP/AMG newer (year 2001 and newer) Optimizer block apparently solved all the defects that plagued the GM 6.5L diesels. I need to get one of these official GEP/AMG Optimizer engines. There are a lot of chinese knock off/GEP/AMG fakes and imitations out there that last a few thousand miles then crack which I'd like to avoid as well. Ted's has some of these apparently but there are a bit pricey for a used, taken out of HMMWV ?why?, uncertain mileage, no warranty engine. Agree the 6.5 L replacement is easiest, as mine is also non electronic. I will go with the newest best GEP/AMG Optimizer 6.5L replacement I can find for now. THANKS!!!

 

[Retiredwarhorses]

Agree. My GM 6.5L engine apparently overheated at some point and had a warped piston and the cylinder in #6 is not cracked but "corroded" and needs to be machined out with a new piston put in. A lot of work or a new block or with a rebuild. The GM 6.5L diesels are loaded with defects and problems apparently. The GEP/AMG newer (year 2001 and newer) Optimizer block apparently solved all the defects that plagued the GM 6.5L diesels. I need to get one of these official GEP/AMG Optimizer engines. There are a lot of chinese knock off/GEP/AMG fakes and imitations out there that last a few thousand miles then crack which I'd like to avoid as well. Ted's has some of these apparently but there are a bit pricey for a used, taken out of HMMWV ?why?, uncertain mileage, no warranty engine. Agree the 6.5 L replacement is easiest, as mine is also non electronic. I will go with the newest best GEP/AMG Optimizer 6.5L replacement I can find for now. THANKS!!!

i have a GEP 6.5 in the shop, it's a blown motor...some lifters are bent and likely a valve or more. its free to whom ever wants to come get it.

 

[GMVguy]

Just saw one on that auction site titled "6.5 Liter Diesel and Transmission (HMMWV)" in North Carolina. Says it's a pull from running truck.