Chevy 6.5l Turbo Diesel.

Ericwc

New member
I’ve got a 98 with the 6.5 in it. It just keeps going. Some a hole stole the radio out of it a few years back cracking the dash in the process. 5 years later I now need to replace the whole dash. 🤬. It does not get driven much but can’t bring myself to get rid of it.
 

BlackPearl

New member
Ive got a 96 2 door with a 6.5, I've swapped the motor twice now and im looking for a 6bt to do the next swap after this one went and grenade'd itself haha. the truck has 678k on it now, the original motor went about 500k the next had 345k on it to start with and went the rest of the way to 678k. The whole truck is getting rebuilt top to bottom in the very near future with a ton of upgrades

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usanumber1

Member
I’ve got a 98 with the 6.5 in it. It just keeps going. Some a hole stole the radio out of it a few years back cracking the dash in the process. 5 years later I now need to replace the whole dash. 🤬. It does not get driven much but can’t bring myself to get rid of it.
I just replaced my dash, it can be tough to find a clean one nowadays. Also, remove the steering column as much as possible, possibly the wheel too. It will help lots if you can have someone help you, it's a big cumbersome sonofabitch.
 

aardvarcus

Adventurer
I have a 1994 6.5L 4x4 Suburban that I am building, replacing almost everything in the process. It is currently running a mechanical 6.5L GEP Optimizer naturally aspirated and a NV4500. I am building it balancing MPG, reliability, drive-ability, and off-road capability. I have been happy with the 23-24 MPG it has been getting, but I will soon begin modifying it to hopefully improve that more.

503658
 

chilliwak

Expedition Leader
Great to see all these cool 6.5 turbo diesels. Thanks for posting up with great pics of your rigs. Aardvarcus can you tell me a little about your optimiser moter? I would like to hear lots of info about that diesel. Cheers, Chilli...🆒
 

aardvarcus

Adventurer
So the short story is that when GM stopped producing the 6.5L in 2001ish, they sold the rights to the U.S. Government who still needed the motor in HMMWV (Humvee). The government got International to fix some of the design flaws with the blocks and metallurgy and do the castings for the engine blocks. This revised engine was named the optimizer. GEP is the company that put them together, you can look up date codes for the casting numbers online to be able to verify if it is a GEP/International block or not. International stopped casting them in the last year or two, they are being cast by another company.

The naturally aspirated Optimizer engines share most dimensions with the Truck version of the 6.5L. The turbocharged Optimizer engines are using the center rear mount turbo like the Van versions of the 6.5L, those are less desirable unless you have a van. There is a even newer version called the P400, which is an upgraded optimizer, however further modifications and a custom oil pan are required to make them work in a stock 6.5l application. The Optimizers have manual DB2 injection pumps (same as 93 and prior GM) and have a lower 20.3:1 compression ratio.

My motor is a 2010 Optimizer and best I can tell it came out of a wrecked HMMWV, since it had the vehicle side motor mounts still attached and torch cut. I bought it from a government surplus reseller. My Suburban came with a 6.5L diesel factory with the DS4 electronic injection pump, but I kept the DB2 mechanical injection pump on the Optimizer engine. I rewired the vehicle to make this work.
 
Aardvarcus, just to clarify some 6.5 history, gm sold the 6.5 to am general. Gep was set up as a wholly owned subsidiary of AMG for the purpose of engineering and production of the 6.5. Most of the design fixes that were introduced under gep were engineered by GM, and just had not yet been introduced. Gep did change the metallurgy a bit with the addition of molybdenum. The biggest improvement that gep made was in machining, cleanliness and assembly quality. The optimizer roughly refers to those engines completely produced under gep control.

The p400 shares dimensions with the 6.5, but utilized a girdle style casting for the main caps. It also had a forged steel crank, unique rods and pistons. All p400 had provisions for a center mounted turbo, a block off plate was used for side turbo applications. A unique aluminum cast pan came on the p400, and without modification it would not fit in the 90s gm trucks due to cross member interference.

Anyhow, just thought I'd try and clarify some of the details that in all reality don't make much difference now. New 6.5s are stupid expe sive due to very low production volumes. Reman can be sketchy for quality unless you really know what you are getting.
 

usanumber1

Member
I’ve been considering buying a used block to rebuild with 18:1 pistons, arp head and main studs, etc because p400 long blocks are mega dollars. My engine is all square and I only have 198k, but I know they day will come.
 

Peneumbra2

Badger Wrangler
When the 6.5 in my '94 3500HD 4x4 took a dump, I yanked it out and replaced it with a Cummins 12-valve. MUCH better.
I suppose that the 6.5 would be enough to power a blazer or suburban, but it was worthless in a 1.5 ton truck.
 
250hp in a 6.5 will usually result in 500lbft, which is what my last suburban had. It towed ok, and was fun to drive, but a juiced Cummins it was not.
 

usanumber1

Member
250hp in a 6.5 will usually result in 500lbft, which is what my last suburban had. It towed ok, and was fun to drive, but a juiced Cummins it was not.
Definitely true. But when you think that just a few short years ago trucks all had 490-520lbft of tq, they all towed great. Maybe not the same as a hot 24valve, but I’ve seen many stock 7.3PSD 250s towing well beyond their legal limit.
 

bknudtsen

Expedition Leader
Good info. Been planning ahead for the eventual replacement of the 6.2L in my ‘83 K10. Was thinking a 6.5 swap might be a good choice to keep things simple. Are there mechanically injected turbos out there? Not looking for huge horsepower, but would like something better than my current 135hp :(
 
Absolutely, if you want to use a stock side mount turbo heath diesel makes a spring loaded waste gate actuator. If it were me, I would find a hx35 and use that. They can be found with a mechanical waste gate stock, and you wont be forced to carry as much boost under light load. The stock gm turbos really work best with electronic control for boost. It takes a lot of power to create air pressure, and making it when you don't need it wasted fuel. The hx35 or the like requires a little fab for exhaust connections and for the oil supply and return, or you can buy a kit off ebay.
 
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