The Next Frontier To Duramax Drivability
Performance tuning is nothing new to the Duramax market, companies like Duramaxtuner of Marengo, Illinois, have been using EFILive software to create custom tuning for the 2001+ GM Duramax for many years. Through continued time behind the wheel and thousands of hours on the chassis dyno, performance ECM software is out there to cover just about any owner’s wants and needs. One thing that has always lagged behind is better control of the Allison automatic transmission, but that’s what sets Duramaxtuner apart.
The 2001-2010 GM Duramax/Allison uses an ECM (Engine Control Module) and separate TCM (Transmission Control Module) that work together to produce the best vehicle performance and efficiency possible. The OEM GM engineers worked tirelessly to match the programming found within the two to create good drivability for every situation. While the aftermarket has focused on the ECM performance side of things, the TCM adjustments have always been a step or two behind, especially in high-horsepower applications. To get a better handle on this, Nick Priegnitz (owner and lead tuner at Duramaxtuner) set out to unlock all the hidden potential within the TCM. While the TCM adjustments will be more noticeable in a modified application (bigger tires, bigger turbos, bigger injectors, etc.) an otherwise stock truck can benefit from the Duramaxtuner matched ECM/TCM files.
First off, since most 2001-2010 GM trucks came from the factory with lightweight 16-inch wheels and 30-inch highway tires, it’s not uncommon for owners to upgrade to a larger wheel and tire package. For those jumping to 35-inch or taller tires, the rolling resistance, rotating mass and overall change in gear ratio can really affect how the truck accelerates. The bigger the tire, the larger the shift extension (rpm drop between shifts), so the factory TCM calibration can have a bit of a “short shift” feel where the engine rpm just drops too far and the engine lugs and struggles to accelerate. By moving the shift point later in the rpm range, the engine will stay in a higher rev range, keeping the engine’s power output where it needs to be.
The next major adjustment within the TCM removes the major defuel felt on the 1-2 shift exchange at wide open throttle. This is much more noticeable with a built transmission and higher horsepower application, but can definitely be noticed in stock transmission trucks as well. Basically, the factory TCM is commanding the ECM to pull fuel before the 1-2 shift to limit torque being sent through the transmission during the shift. Obviously once a transmission has been upgraded, it can handle a much higher torque load, so the big defuel is no longer needed as a “safety net.” The defuel can be programmed accordingly to maintain a smooth forward motion from the truck, but this does require the ECM and TCM programming to be matched for best results.
In six-speed applications, the overdrive and double overdrive gears can be a little reluctant to downshift, which keeps rpm low, this keeps the truck from accelerating on the highway like it should. Sometimes the driver will have to apply more than 80 percent throttle to get the downshift to happen, usually when passing, but once that downshift happens, because you’re at such heavy throttle input, the ECM is commanding a lot of fuel so the power output is extreme and makes the truck jump and behave erratically. The Duramaxtuner TCM allows the downshift from fifth and sixth gear to happen at a lower throttle percentage at lower rpm, so the truck will effortlessly find a lower gear, create boost, and accelerate around someone much easier.
Lastly, for the big turbo crowd, rpm can become your new best friend and the TCM adjustments can make a truck much more friendly on the street. Running a large 72+ millimeter turbo requires a higher rpm range to stay within its map, so extending the shift points and allowing earlier downshifts will make the truck quicker to respond to throttle input.
For the competition crowd, the new TCM programming can also be set up specifically to meet your needs on both the sled pull and asphalt drag track. Since most sled pull applications are running big, single turbos that can be hard to light, Duramaxtuner can set the TCM up with second or third gear starts when running in four-low. By avoiding first gear all together, the TCM can command a second or third gear launch from the starting line, which will allow a much heavier load to be placed on the
engine to help spool a big turbo.
Similar tweaks can be made for the drag race crowd with second gear starts when running in ‘Tow/Haul’ mode. This allows a harder load to be placed on the engine for more boost on the line and prevent the truck from creeping through the brakes at the staging tree. Launching in second gear can also make for much more consistent 60-foot times, due to the smoother launch and lack of the 1-2 shift happening so quick after you leave the line.
TORQUE CONVERTER CONTROL
Better torque converter lock-up is also achieved within the TCM tunes to improve power transfer to the ground. As horsepower continues to climb it becomes much harder for the torque converter to fully lock under heavy load due to some limitations within the factory TCM programming. While under normal load the T/C may lock between the 2-3 shift as commanded, but once the throttle goes wide open and power and torque output skyrocket, the TCM delays the T/C from locking until much later. Third, fourth even fifth gear lock-up is not unheard of in big-power trucks. So rather than locking when you want and need it most, sending 100 percent power to the tires, the transmission just delays, slips, creates excessive heat and wastes energy.
“Launching in second gear can also make for much more consistent 60-foot times.”
The Duramaxtuner TCM files will eliminate this altogether thanks to minor adjustments made within the torque converter’s lock-up tables in the programming. By improving the commanded pressures and rpm control of the lock-up clutches, there’s no more delay and second guessing within the TCM. Converter lock-up happens when it’s commanded, stab the throttle and there the converter will be, fully locked and ready to take all that torque to the ground.
For competition guys, sled pullers and drag racers alike, the new TCM programming can also eliminate the need to run a separate lock-up control box. So no more buttons to push to command lock-up as you go down the track and no more remembering to unlock at the end of the track either. You can focus on driving and let the truck and Allison due its own thing, without questioning its consistency.
To get a better feel for what the crew at Duramaxtuner was talking about, we opted to install the matched ECM/TCM files in two different trucks we could spend some time driving, getting honest before and after input. The first truck was a completely bone-stock 2006 LBZ GMC. The SPADE tuning device from Duramaxtuner had been preloaded with their DSP5 engine tuning and matched TCM files. Limited by the stock transmission, the SPADE offered up to 120 hp over stock, but we spent most time driving in the 80-hp file as it seemed to be best for daily driving. Within the first few tanks of fuel we noticed much better throttle response, easier downshifts and just an overall improvement in how the truck moved itself through town and down the highway, plus we also netted 2 mpg increase in fuel mileage.
5 The SPADE (Standalone Programming And Diagnostics Equipment) offers what Duramaxtuner states as the highest quality tunes on the market via an OBD-II flash tool. This handheld device contains fully matched engine and transmission tuning to turn the average daily driver into a true performance vehicle, whether that means better power while towing the families RV down the highway or blowing through the traps at the local 1/4-mile drag strip.The second test vehicle was a 2002 LB7 Chevrolet running a host of modifications, 67mm single turbocharger, built Allison transmission, intake and exhaust upgrades, fuel lift pump and 33-inch tires. The truck had already been tuned with Duramaxtuner ECM files and had been dyno tested at close to 600 hp, so the owner already knew the performance potential of the truck, but the factory TCM tune was definitely a limiting factor in drivability. Running the new performance TCM files turned it into an all-new truck, with more consistent performance, more predictable gear exchanges with solid converter lock-up at heavy throttle input. No changes were made within ECM files, so there was no increase in power output, but from the seat you could just feel the truck working better. Shifting quality was improved, defuel felt more appropriate, and the truck was much more responsive and fun to drive.
The matched TCM and ECM tuning software offered by Duramaxtuner really can turn just about any Duramax into something closer to the ultimate driving experience. The broader power and torque curves from ECM changes make towing, daily driving and competing more enjoyable while the perfectly matched TCM software ensures all that power is put to good use, efficiently and effectively. DW