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Duramax Performance


Please read for information on Duramax modifications!!

A Note from John Kennedy.....

You can see my trucks accomplishments here:

As a Duramax owner, I test the products that I sell on an ongoing basis with my own 2002 Chev K2500. I perform these tests on the road towing AND on my Superflow SF 840 Chassis Dyno. Some are my own design and some are from others. I run the Uni-Filter foam air filter, the KD 4" into 5" performance exhaust system and use the SPA DG 211 digital dual gauge to keep an eye on things. I have run most every power box out there and if you don't see it listed under chips, it likely isn't worth having. By using these items on a daily basis, I get to know these items intimately and can provide the service to back them (and other items) up should the need arise. With the addition of my Superflow dyno, I am even better equipped to test and authenticate the performance gained by a modification! I have dyno tested this truck at over 530 RWHP on diesel fuel only, 730+ on nitrous and that is just the beginning!

Engine Identification:
The Duramax engine has evolved from the original LB7 series to the LLY, then LBZ, and now the LMM series. The LB7 was used from 2001 model year until mid 2004 model year. In mid 2004 the LLY series was released. In 2006 the Duramax changed again. The early 2006 engines were still called LLY and the later 2006 and 2007 "Classic" became the LBZ. This creates some confusion as the 06 LLY is distinctively different from the 04.5-05 LLY. The 2006 LLY and LBZ engines are essentially the same when it comes to modifications. The LMM began in the new body style GMT 900 series trucks in 2007 and continued through 2010. In 2011 the LML was released and is currently in use through 2015 and beyond??? The simplest way to verify which series you have is the VIN# of the truck. The 8th digit is the engine ID and it will either be a 1, 2, D, 6, or 8.
Example: 1GCHK29143Exxxxxx for LB7 and 1GCHK29245Exxxxx for LLY. It is important to know this as while the engines are essentially the same at the core, the electronics, turbochargers, electronics, and injectors are different among the variants.  The 10th place in the VIN number identifies the model year on these vehicles.  The example above shows the 2003 model year LB7 and 2005 LLY. 

Making Power:
The first place to start with modifying any diesel is to upgrade the intake and exhaust system. While it is tempting to go for quick and easy power of a module, in order to extract the full potential of these boxes and maintain reasonable exhaust temps, we MUST move more air! While the Duramax burns very cleanly, and will perform adequately with just a box, more air will still boost performance, while providing increased throttle/boost response, and cooler exhaust temperatures.

Choosing a chip:
First we'll start with the basics. With the Duramax, the term "Chip" is loosely used to describe 3 different types of modifications: Tuners, Harness Box, or Custom Programming. It is my opinion, that most off the shelf mods for the 2005+ Duramax engines are sorely lacking in refinement. The introduction if the variable (tunable) geometry turbo has seemingly been ignored as nobody seems to be up to the challenge of tuning it. It seems that most feel that adding timing and fuel gains HP and gets results so that is good enough. I disagree. While we do have items to band-aid these inferior tunes (Boost Stick, Blocker pkg) I see much better results from my Kennedy Custom Tuning.

Tuners are hand held devices that contain modified tuning that is written to your factory ECM through the ALDL port under your dash. They require no hardware to operate the vehicle. The hardware is only necessary only to load or make changes. A typical tuner will have save out your factory stock tune and retain it in memory so that you may restore it at a later time if desired. They also typically contain multiple 'tunes' of varying performance available to be loaded based on personal preference. A tuner can also typically correct the speedometer for tire size, and increase the vehicles top speed limit beyond factory. Some tuner's can read and clear fault codes and some can even monitor real time engine data. Off the shelf tuners are kind of like the old saying: jack of all trades, master of none. They do a little bit of everything, but nothing particularly well.

Harness Boxes:
This term describes chips that use “ride along hardware� to do their job. This hardware can contain simple electronics, OR full blown microprocessor circuitry. They generally intercept various signals from the ECM or direct from the sensor and alter or recreate them. The better harness boxes generally connect quite simply and easily at the two large engine data harness plugs above the LH rocker cover. Some lesser units attach directly at the sensor. These devices are typically quite crude and contain simple “fooler� circuitry which provides lesser performance. A typical harness box can “cap� boost signal to eliminate overboost codes and also focuses on injector pulse width (on time) and timing. They are typically limited in how dynamically they can alter timing, and CANNOT correct speedometer or factory speed limiters. They can include EGT (exhaust gas temp) probes that can be used to back out their additional power, and can include monitors to monitor critical engine data. They can also monitor transmission slip speeds and back out their added power in the event of a slip. Examples of harness boxes include: Edge Juice and EZ, Van Aaken Smart Box, Bully Dog Dyno Dominator, etc. My preference here goes to the Edge Juice. The Edge isn’t the strongest or fastest, but performs quite respectably. It does an excellent job towing and is one of my personal favorites for performance and response under load. The Van Aaken Smart Box is also an excellent performer, just a bit more “laid back� when it comes to response. The VA 200+ is an all around excellent performer so long as you have enough transmission to hold the power.

Custom Programming:
This is what I currently run and has allowed me to take things to the next level both in performance, and in economy. On the surface, the general nature of my Kennedy Custom Tuning (available for all LB7, LLY, LBZ, and LMM) differs very little from the typical tuner in that the modifications are made to the software on the vehicle ECM. Where the key difference comes in is that my tunes are generally quite a bit better than your average tuner. The average "off the shelf" tuner is built for the masses and has lesser, simpler modifications performed. The tuner is allowed very little time to perform his work and must tune a wide variety of vehicles. Once released to the public, very little further development occurs unless there is a bug. I own my test vehicles and drive them putting me in much better touch with how the Duramax operates. You can also try your own hand at it with a product called EFI Live. This product allows you top make all the changes yourself. In my case, I use the EFI Live product to create my tunes then apply them to an actual ECM. Once the tune is applied the ECM is "locked" so that it cannot be overwritten or copied. All diagnostic functions like code reading still perform properly. My programming can either be loaded to your ECM or one of my core units. I have numerous tunes available ranging from simple 30-40HP economy tune to High Torque Tow tunes to 100-250HP+ race tunes. My focus has been to provide excellent drivability with greatly improved responsiveness along with improved fuel economy on ALL tunes often including the race tunes. My tunes include DSP2 selectability (LB7 and LLY only) where a simple toggle switch is added and allows the user to switch on the fly between two different tunes. These two tunes can be set to most any power level desired.

Additional Notes:
The Duramaximizer and Dynomite are pressure type harness boxes. The KD Custom Tuning, Edge Juice/BD EZ-Amp, TTS Power Loader, and Van Aaken Smart Box E, are pulse width (injector "on time") and timing type boxes. The pressure type boxes are the simplest, and were the first to market. Since then, trend has been to shy away from the pressure type box due to occurrence of fuel leaks in even stock trucks. The pressure type boxes have stuck around though as they can be used to "stack" with the pulse width type boxes for extreme race applications. That said, the pulse width type modifications produce much more power than any of the pressure boxes regardless of HP claims AND bring it in earlier making them my clear choice for towing applications. When reading HP claims, one must realize that some claim flywheel, and some claim rear wheel figures. With the addition of my Superflow SF 840 chassis dyno, I now have the ability to test these under load in house as well as on the road whether it be a race program or tow program!

Allison Transmission:
The Allison transmission is a very durable unit. It is also quite smart in that it will protect itself from serious abuse by "limping" if it sees excessive slippage. It seems that the point of limp varies from truck to truck, but suffice to say, if you cross 700lb/ft at the wheels, you are entering the questionable zone for a stock transmission. My dyno testing shown that the torque converter clutch appears to be the first weak link.

With the ability to regulate the load applied, I control acceleration rate simulating the real world. I've found that most transmissions do not like over 725 lb/ft of torque or the converter will slip. If you want to play it safe, stay below 700lb/ft and use a box like the Van Aaken Smart Box E, Edge Juice, or Banks 6 Gun. Either of these boxes will enhance the transmission protection by reducing their added power if slip is detected.

Dyno chart

Whenever working a diesel engine, whether modified or stock, it is a good idea to have a pyrometer to monitor exhaust gas temperatures. A boost gauge is also particularly useful to compliment the pyrometer. Knowing what your exhaust gas temperatures and boost levels are allows you to gauge how hard the engine is being worked, and adjust your load and driving style to keep it within safe limits. Whenever we add a performance module, the potential for increased exhaust temperatures (sometimes above the safe operating limits) exists. In the short term, this can be acceptable, but running this way for extended periods of time can cause damage to the engine. Knowing what is going on when working (or racing) your engine is critical! I run the SPA DG211 digital dual gauge mounted in the overhead console on my 2002 Chev and the Isspro R3607T pyrometer with the R 5613 in a 2 gauge pillar mount on my 96 GMC.

Fuel Economy:
Most modifications should not detrimentally affect fuel economy of your diesel engine, and on the contrary, often actually improve economy. Since diesel operation is regulated by fuel delivery, YOU ultimately control the economy. The modifications listed here increase the engine's combustion efficiency, and since a diesel engine only requires a given amount of fuel to do a job, if we increase the efficiency of the engine, we can see MPG gains! It should also be noted that abuse of this new found power CAN reduce MPG. It's all dependent on your right foot...

Warranty Issues:
Most modifications shown here should not cause warranty concerns but remember: "Out of sight = Out of mind!" Any of the modules/programs listed her can be removed and there is really no way of detecting their use by the dealer. Now as for warranty issues, YES the dealer can refuse warranty due to the use of ANY module. There is the Magnusson-Moss warranty act that says the dealer/mfr must prove that the aftermarket device caused the failure directly, BUT the long and short of it is this: THEY hold all the cards, and in most cases, what they say goes. It all depends how much time/money you have to throw into a court case IF the need should arise! Again, "Out of site = Out of mind..." Try to keep on the good side of your dealer, and HOPE he/she is open minded! Please note: 2007.5 LMM ECM's have a lookup table that GM can check see if a tune has ever been installed. This is also a likely possibility for 2006+ LLY and LBZ as they use the same controller. For this reason, I strongly recommend that you never tune your factory ECM. Always tune on a core unit from Salvage. Most of my Kennedy Custom Tuning is done on core ECM's for warranty preservation.