View Full Version : 6.2/6.5 Turbo Diesel Performance toolbox

02-07-2013, 09:44 AM
Taking a cue from how things were written up for the gas versions of our trucks figured it was time to do something similar for the Diesels. This thread will contain common upgrades to the 6.5 powered trucks and eventually some setups to bump up the performance.

Lets start with a bit of history of the engine itself

Quoted from Wikipedia


The original 6.2 L (379 cu in) Diesel V8 was introduced in 1982 for the Chevrolet/GMC C/K trucks and was produced until 1993. The 6.2L diesel emerged as a high-MPG alternative to the V8 gasoline engine lineup, and achieved better mileage than the General Motors 4.3L V6 gasoline engines of the 80s, at a time when the market was focused on mileage more than power.
19821993 Chevrolet/GMC C/K
1992 - 1993 AM General Hummer H1
198x - 1993 AM General HMMWV
GM version of the CUCV
1982-93 Chevrolet Van
Engine RPO Codes: LH6 ('C' series, with EGR) and LL4 ('J' series)
Displacement: 6.2L / 379 cu in
Bore x Stroke: 3.98 in 3.80 in (101 mm 97 mm)
Block / Head: Cast iron / Cast iron
Aspiration: Natural
Valvetrain: OHV 2-V
Compression: 21.5:1
Injection: Indirect
Horsepower / Torque (at start): 130 hp (97 kW) @ 3,600 rpm / 240 lbft (325 Nm) @ 2,000 rpm
Horsepower / Torque (at final): 143 hp (107 kW) @ 3,600 rpm / 257 lbft (348 Nm) @ 2,000 rpm
Horsepower / Torque (army): 165 hp (123 kW) @ 3,600 rpm / 330 lbft (447 Nm) @ 2,100 rpm
Max RPMs: 3,600
Idle RPMs: 650 + or - 25


The 6.5 L (395 cu in) version was introduced in 1992 to replace the 6.2. Most 6.5s are equipped with a turbo. This engine was never meant to be a power and torque competitor with Ford/International and Dodge/Cummins, but rather a simply designed workhorse engine that made credible power, achieved decent fuel economy and met emissions standards in half-ton trucks. The Duramax 6600 replaced the 6.5 in light trucks beginning in 2001 and the C3500HD medium duty cab and chassis (replaced by C4500 Kodiak/Topkick) and vans beginning in 2003, but the 6.5 (6500 Optimizer) is still produced by AM General for the HMMWV.
There are several GM 6.5 liter diesel engine production options. The Turbocharged L56, (VIN "S") was used in most light duty 3/4 ton (2500) Heavy duty 3/4 ton and 1 ton trucks used the Turbocharged L65 (VIN "F") engine. The L56 is emissions controlled with EGR and catalytic converters. The L65 engine has no EGR, and has no catalytic converter. There is a soot trap on L65 engines that is often mistaken for a catalytic converter. The L49 (VIN "P") and L57 are both naturally aspirated engines. L57 is listed as HO or Heavy Duty. Additional RPO codes are LQM (175HP) and LQN (190HP).
Changes were made by GM to the 6.5 in their light trucks for emissions or reliability improvement. The 1992-1993 model years used a 6.5-specific Stanadyne DB-2 mechanical injection pump. GM replaced the DB-2 with the electronic throttle DS-4 in 1994-2000 vehicles. In mid-1996 GM implemented a redesigned engine cooling system incorporating twin non bypass-blocking thermostats and a 130 GPM water pump. This improved the flow through the block by 70-75% and flow to the radiator 7%.
1994 - 1999 Chevy Blazer/ 2-door Tahoe / GMC Yukon/Chevy K-2500,K-3500
1992 - 1999 Chevrolet Suburban / GMC Suburban
1992 - 1999 Chevrolet and GMC C/K
2000 Chevrolet and GMC C/K 2500 & 3500
2001 Chevrolet and GMC C/K 3500
1994 - 2004 AM General Hummer H1
1994present AM General HMMWV
Engine RPO Codes: L49, L56, L57, L65, LQM, and LQN.
Displacement: 6.5L / 397 cu in
Bore x Stroke: 4.06 x 3.82 (in.)
Block / Head: Cast iron / Cast iron
Aspiration: Turbocharged (Borg-Warner GM-X series) Also available naturally aspirated.
Valvetrain: OHV 2-V
Compression: GM Early 21.3:1, GM Late 20.3:1, AMG/GEP Marine 18:1
Injection: Indirect
Power / Torque (lowest): 180 hp (134 kW) @ 3,400 rpm / 360 lbft (488 Nm) @ 1,700 rpm
Power / Torque (highest): 215 hp (160 kW) @ 3,200 rpm / 440 lbft (597 Nm) @ 1,800 rpm
Max RPMs: 3,400

Fuel system

The fuel system is a very simple design. A mechanical or electric fuel lift pump feeds a Stanadyne Rotary Distributor Injection pump at low pressure. The distributor injection pump controls both timing, via an internal centrifugal governor, and high pressure fuel delivery to the fuel injectors via internal precision hydraulic pumps. Near the top of the compression stroke fuel is atomized at high pressure into a hemispherical Inconel prechamber in the cylinder heads using Bosch pintle and seat mechanical fuel injectors. This is called Indirect injection. GM used fully mechanical DB2 series injection pumps on all military HMMWVs and 1982-1993 6.2's and 6.5's. From 1994 till end of production GM used the electronically controlled Stanadyne DS4 series of injection pumps in their light trucks. A mechanical DB4 series injection pump can be found on some 6.5L marine engines.
[edit]Common Problems

Main Bearing Web Crack: In both 6.2L and 6.5L engines this is reportedly fixed with a combination of improved higher nickel cast iron alloy and lower block re-design including, but not limited to, a main bearing girdle. These features are in the new for 2007 AM General GEP P400 6500 Optimizer enhanced 6.5L diesel presently being sold to the US Government for the 6 ton armored HMMWV.[1]
Crank Failure: Related to age failures of the harmonic balancer, the vibration damped accessory drive pulley, or the dual mass flywheel.
Pump Mounted Driver: Relates to thermal failures. The PMD is screwed to the DS-4 injection pump on the 1994-2001 GM 6.5 diesel utilizing fuel flow to dissipate heat. The injection pump is mounted in the intake valley (a high heat area). The PMD contains two power transistors that should be cooled by proper contact with the injection pump body. If the pump is not precisely machined to make complete contact with the transistors via the silicone thermal gasket and paste, the PMD is improperly installed without the gasket or paste, the PMD is installed off center with the pump body, or corrosion develops on the mounting surface the PMD will overheat. Several companies manufacture an extension harness and heat-sink kits. These allow an owner or their mechanic to relocate the PMD away from the injection pump to a lower heat environment and/or a place that can get more air flow.
Cylinder Head Cracking: higher mileage 6.5 engines exhibit stress related fractures in the cylinder head bowl. Stronger cylinder heads remedy this problem.

Now that the History is out of the way on to the Upgrades for durability

PMD Relocation

Here is the How to i created not long after i joined this forum but i will also include the info of the whys and hows here.

PMD Relocation (http://www.gmt400.com/forum/showthread.php?10455-How-to-PMD-FSD-Relocation-on-a-6-5-Turbo-Diesel-and-why-it-needs-to-be-done)

To start with the process of relocation and the pros/cons of each method.

1st method: Intake mounted heat sink

Initially when this weak point was discovered the aftermarket responded with various kits to move it from the pump to a heat sink bolted to the intake.


Moves the pmd to a slightly cooler area


Still inside the hot engine bay

2nd method: relocation to inside air box with a heat sink or fan.

Some owners have moved this lil black box to inside their flat panel style air cleaner housings with either a computer fan and/or a heat sink.


This works marganally better then method 1 in that it adds the air flow from the incoming air headed to the filter. As well as adding shielding.


Same as method 1

3rd Method relocation outside of the bay to either the rad support or bumper.

This is the method I will be explaining in this thread. Like the original 2 methods it adds a heat sink plus moves the box into cooler air, however this is much much cooler air, It takes advantage of the cooling ducts in the Diesel bumper plus uses the bumper as a heat sink itself.

Finally moves the pmd out of the hot engine bay
Much better cooling then the airbox method
Takes advantage of another design feature of the diesel trucks.

Possible exposure to moisture, Not a major risk as long as the seals on the weatherpak connectors are still good. and if you are going into deep water deep enough to affect it in this placement you prob should have it well siliconed or in the cab,

Now onto the pics and how to:

This is the pmd it arrived preinstalled on the heat sink, there would be a coiled harness here as well but by the time I took this pic I already had it installed on the truck.


To begin with you remove the right side signal light and you will see a hole in the rad support for the ac lines, thread the harness through this hole as you can see this has already been done.


Then you route the harness to a point it can be plugged into the original pmd plug once again already done. Note: routing will vary depending on if you are redoing a previous relocation or not. In this case the truck used had the air box method done so I had about a foot of extra wire to deal with.


Then route the other end through the cooling hole in the bumper long enough to plug in the new pmd then feed the entire unit through the hole and bolt it to the bumper using one of the license plate mount holes, depending on if you have the mount still or not you may need to use washers.


Reinstall the signal light and you are done,

Enjoy having to not worry about having to access the pmd on a hot engine again and ease of replacement should the new unit ever fail.

A brief explaination as to why to relocate the pmd/fsd

I bet lol, and forgive me for sounding stupid but is a PDM like a PCM?

Kinda. It controls the Drive By Wire throttle in the truck. Basically if it over heats..no throttle, no fueling really. PMD stands for Pump Mounted Driver. Since when these trucks first came out all the way till the Dmax replaced the Detroit 6.5 The lil black box has been bolted directly to the Injector pump which is right in the center of the V of the engine. Roughly where your thermostat housing would be on a gas small block engine. But it was prone to overheating thus the problems mentioned above. The proper fix is to mount it on a heat sink and relocate it out of the engine bay. Which is what i will be doing once my new PMD and relocation kit arrive. Mounted in this configuration it is refered to as a Fuel Solenoid Driver or FSD for short.

02-07-2013, 09:49 AM
Feed the Beast

I will add more info to this this weekend once i dig up the threads i learned about it on.

The basics:

Increasing the size of the lines between the Fuel Filter Manager (FFM from this point forward) and the Injection pump.

Method #1:

Removing the FFM from the truck and machining the housing to accept AN fittings with the larger line size.

Method #2

Replace the FFM with a remote mounted filter head and spin on filter with the larger output on it. This is the method that was employed on my own truck.

Usually the Feed the Beast mod is done by upgrading the line between the two points from its pathetic 1/4" line up to 5/16" or 3/8" matching the size of the line going into the FFM.

02-07-2013, 09:55 AM
The following is a conversation between myself and Great White in a thread we accidently jacked this morning.

Nah, I'll pass on that one friend.

I'd rather have an lb7 or an lbz in there and be able ro ditch the pad altogether. Just enough to know ot's not a gasser, but civilized just enough to slip on by unnoticed 95% percent of the time.

And; you don't have to shut the damned thing off at the tim hortons drive through so the girl can hear your order....

I really like my diesel and wouldn't switch back to gas (can't with the 35 foot trailer!). But I would switch up to a newer one. Even with the increased cost of repair parts I'd still switch up.

Early 80's tech gets so tiresome sometimes.....Not to mention limiting what you can do with it.

My 65 is about as "hot" as you can get it without sacrificing reliability and I'm just barely scratching stock 2001 lb7 territory with 271 and 440 ish rear wheel. Throw a box time at an lb7 and a 65 is left in some serious dust. If i had the money into an lb7 that i have in my 65, i'd be knocking on 700-800 rwhp...."if I knew then what I know now"....

When the 65 calves (hopefully not for another ten years or so seeing what I've got into it), an lb7 is going in there.

No doubt "aboot" it.


I'm thinking I may need to pick your brain sometime to see what you did to get there..I know im def getting in contact with Westers Garage at some point. If I remember right you have a 4" diamond eye exhaust and some computer tweeks but what else?


New optimizer, wmi and writing/flashing my own calibrations are a big part of it....plus most of standard 65 stuff you probably already know...

Ahh ok, yea so far I have my pmd relocated, and ftb done. Well that and and advanced ip which I will be replacing with a new one this spring. Been eying up the stage II chip westers offers for the obd 1 6.5s, I'm def gonna look into getting a holset and 4" exhaust over the summer.

Yeah, thats a fine plan.

Won't get you to where I am but you can expect somewhere right around 200-210 hp.


Thats one of my last runs from the past summer. It's an iphone app, but it works like a gtech. I've had it on a dyno and the numbers are close enough. The yellow is hp, the proggy doesn't calculate torque.

I'm also still running the gm8 and vac system......


Nice, just enough of a boost to have some extra grunt but not so much that im risking reliability.

Im talking crank hp, not rwl.

Probably more like 180-185 rwhp.....Most stock 65 TD put around 160-170 to the rollers depending on the truck (auto/standard, etc) and the dyno operator. Those guys can give you messed up numbers depending on how they set up the rig. Different types of dynos give different results also.....

Ahh ok, what would I be looking at torque wise?

Dunno, its a pure guess but around 350-380.

You can work the math both ways yo establish the target you want: HP = Torque x RPM 5252

Basically, a 65 is pretty much all in around 2500. Theres some more above 2500, but it's not all that practicle or cost effecient chasing it. 3 grand is where the average joe will want to stop pushing it for sure. 3400 is for noise, pulling way more (or faster) than the truck should or drag racing (in a 65? Yeesh) it.

Depending on what you're planning for a holset, you may be able to go 3000 before you start to egt out on a hard pull.

I started with the rpm range i wanted to peak (determined by the limitations in the parts choices) then chased the highest tq iIcould achieve. Fuel rates, timing, boost, when the turbo comes on and runs out, etc. i was a fune day at the shop on the duno. We all had a great time working on something they usually don't get a chance to.

The hp is just a function of the above equation.

HP = Torque x RPM / 5252

Just in case the formula was messed up by the hypercoding.

Doesn't come through as a "divided by" symbol on my iphone...

Interesting bit of trivia:

If hp and torque don't cross at 5252 rpm, you've made a math error.

It's a constant of the equation....