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6.2L & 6.5L Performance Discussion of Chevy and GMC Trucks with 6.2L and 6.5L Diesel Engines Related to Performance and Longevity

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Old 05-28-2015, 03:34 PM
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So I just bought my first truck and it's a 97 Chevy 6.5 k2500, and I'll be honest I don't know much about these specific motors but I did my research and these motors are not exactly powerhouses like a 7.3 or 5.9 but what's the best performance I can get out of this thing??
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Old 06-21-2015, 12:42 AM
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Depends on how much $$$ you wanna toss at it. You gonna dual turbo with manual pump marine injectors and alcohol injection? Bill Heath got 500hp outta a 6.5l 500hp 6.5L Diesel Race Engine - Diesel Power Magazine
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Old 06-26-2015, 12:03 AM
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Since you have no intercooler, watermeth would not be a bad place to start. Get more efficiency and power. You can even piece a kit together with Isspro EV2 gauges and relay system where you can have it spray at 10psi.
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Old 10-20-2015, 12:05 PM
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where are you on this project , performance = $$$ how much do you want to spend, and how healthy is the platform you are starting with what is the purpose of the build, street or tow or general improvement overall for both ?

A 6.5 can be brought to performance of a mildly modded Dmax with a smart build because we are dealing with an IDI engine we will not be able to match maximum performance a fully built DI engine delivers, but the 6.5 can be built to smoke stock DI equipped and a number of gasser engined vehicles and get their respect.

Baddest 6.5 I know of is Bill Heath's Bonneville racer
but a MAJOR project that one.

Last edited by Turbine Doc; 10-20-2015 at 12:10 PM.
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Old 10-21-2015, 08:23 AM
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Start with 4" exhaust. If you are in the rust belt, go stainless. It's not that much more money. I like the removable down pipe with a clamp or bolt connection to the exhaust pipe.

I have an aluminized system on my truck and am having to replace the down pipe as it rotted off.

Heart Throb makes a stainless system and a connection for a removable down pipe.

The feed the beast mod,

watch your engine oil cooler lines. Do not waste your money replacing with any OEM style lines. Get a kit from Espar Heater Parts, EZ Oil Drain Valves & More Industrial Products by the Lubrication Specialist or make your own.

Keep your OEM K47 air box. It will provide plenty of air unless you get crazy.

The ATT turbo is said to be a good upgrade.

Use only ACDelco 60G or Bosch duraterm glow plugs.

If staying with OEM style lift pump get ACDelco or GM for a 1993 They have more flow. I also heard there was a new number for 2000 and newer that also has better flow, but I can not verify that.

I like the battery bolt mod. I use 1 1/4" stainless 3/8-16 Allen screws instead of bolts. Cut or grind the ends to near square instead of tapered.

I add grounds to the Stud by the firewall that all the little grounds go to, to the battery box bolt - you have to pull the battery, to the injection pump, to the frame by the starter and from the heater blower to the dash mount bolt, just inches away

A good set of battery cables like Raceday mechanic makes is a good upgrade.

For longevity I add a bypass filter either Amsoil or FS2500. I tap off the return line - just behind the radiator - from the engine oil cooler to supply the filter and return to nipple welded to the oil fill neck. I install a T when I install the braided stainless engine oil cooler lines.

I leave the OEM oil filter as is and mount the bypass filter under the hood.

I am a firm believer in Amsoil and change the oil every 20,000 miles, though oil samples say I could go longer. I use 5W30 heavy duty diesel oil.

I am currently using Mobile 1 synthetic 5W40 diesel oil because it was on sale for $10 a gallon. I do not like it because Mobile does not recommend running extended oil change intervals. By the time I pay for twice as many oil filters the savings is not that great.

I run synthetic fluids throughout.

We've got way over 2 million miles on our vehicles totaled up. We're either lucky or it's the filters and oil. Average right now is about 310,000 miles per vehicle - without the 89 that I put 800,000 miles on or the International with 500,000 miles

I use Amsoil or Baldwin filters

Add fuel additive every tankful. Some type of lubricity additive.

I open the T drain every 5000 miles or so and run about 1/2 gallon out.

Be careful what you spray and where you spray it. I had some brake clean that I thought was plastic safe and watched melt some corrugated plastic wire sheath in short order. rEMEBER THAT ALMOST ALL THE ISSUES WITH THESE VEHICLES ARE electric related. These old engine harnesses get brittle fast. Using the wrong chemicals can mess things up fast.

I have been changing the engine harness on my vehicles as I work on them. They all have broken clips here or there or other indications they are getting brittle.

Glagulator at has made me a couple harnesses - The only place I have found a new harness. They are nice harnesses and have had zero issues

Keep a spare PMD. I have 2 mounted on heat sinks in my front bumper. One pointed towards each nostril. I mount the heat sinks so the plug points towards the nostril. On some I have had to turn the PMD 90 degrees and tap new holes. So the plug is where I want it. They mount to the front license plate bracket bolt. Even if I have to pop rivet a piece of aluminum angle to the side of the heat sink, I make them mount the way I want them. The plugs end up just inside the nostril, Very easy to reach in and change the plugs.

The only PMD I will use is the Flight Systems from

I had 3 bad gray Standyne PMD's. I have no experience with the Dorman PMD's.

Last edited by jrsavoie; 10-21-2015 at 08:50 AM.
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Old 04-07-2016, 10:35 AM
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I have a 1994 k2500 6.5 non turbo which i had a few questions about because i know the non turbo have more compression i think than the turbo engine
NA - 21-3-1
Turbo - 20-3-1
is what i found which leads me to my first question in order to turbo besides having to have manifold ect. would you need head studs for a NA?
Another thing does anyone know of an in cab tuner NOT A CHIP but a tuner for a 6.5?
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Old 04-28-2016, 09:03 AM
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No "in cab" tuners for 6.5 the PCMs pre-date that technology so you have to have either the chip or the PCM in later years reflashed.

Do you have a mech or an electronic IP ? if mech, you can adjust IP for more fuel when swapping over to turbo, and also ad a mech WG control if trying to use a OEM type turbo.

My preference would be to get a ATT turbo A-Team Turbo | , as that does away with any subsequent adjustments of the WG you will have to do plus gives better mpg than OEM and other aftermarket turbos.. Documented 1-3 mpg gains on MANY, most if not all ATT installs plus extra performance and pulling power.
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