Duramax Diesel Engine Horsepower & Torque Uprgrades- Dura Maximus

When it comes to hauling heavy loads, the General Motors 6.6L Duramax turbodiesel does an impressive job right out of the box. However, under heavily loaded conditions and when pitted against the torque-hemorrhaging Cummins or rev-happy Power Stroke, all the high-tech Isuzu-designed internals still fall short. That's why we decided to take on a friendly challenge from a buddy to build a severely fast Duramax truck. Not just a truck with a fueling box that makes a little extra power and a lot of black smoke, we wanted a Duramax that could literally blow the doors off just about any other truck on the road. In the end, our donor truck put down an outstanding 1,090 lb-ft of torque and 542 hp. Follow along as we show you how we did it and why.

The Truck
We started with an '05 GMC Sierra 4x4, extended-cab shortbed. This vintage of the Duramax received the designation LLY and was rated from the factory at 310 hp and 605 lb-ft of torque at the flywheel. Ours had roughly 70,000 miles on the ticker and was well maintained. Our truck was a non-California emissions vehicle and remained pretty much stock aside from Hanson bumpers, a set of Pro Comp wheels, a few minor suspension tweaks, and a 15,000-pound Warn winch. We figured the truck represented what our average diesel enthusiast reader might own. The only uncommon thing about our donor was the fact that it had the somewhat rare six-speed manual transmission instead of the Allison automatic. Our first order of operation was to dyno-test the rig in stock form. We enlisted help from the dyno gurus at Westech Performance Group in San Dimas, California, because of their reputable background in generating non-arguable data. During the initial dyno pull, our Duramax put down a predictable 241 hp and 456 lb-ft of torque at the rear wheels-not bad for a factory rig.

Upgrades, Part 1
Next, we secured shop time with our friends at Overkill Jeep Fabrication in Campbell, California. With the truck on a lift, we installed a Centerforce dual-friction clutch. Common knowledge about the stock clutch in a Duramax pickup typically predicts clutch slippage around 650 lb-ft of torque. The new Centerforce unit, with its patented dual-friction disc system, distributes clamping force evenly over a 360-degree frictionfacing on one side of the clutch disc, while the opposing side uses a segmented friction-facing to concentrate clamping pressure and maximize clutch-holding capacity. Centerforce claims this clutch will hold up to 720 lb-ft of torque. While we do plan to exceed 720 lb-ft of torque on this project, we could not source a different clutch for our application. So, we'll just have to see how long it lives for now.

Upgrades, Part 2
After several thousand miles of clutch breakin, we decided to proceed with our second round of modifications to the truck. We dropped the rig off with Steve Cole, owner of TTS Inc. of Compton, California. Steve is well known in the diesel aftermarket community for his unrivaled successes with custom programming on Duramax pickups. Having multiple racing wins associated with his aggressive ECU tuning, Steve relies mostly on word of mouth amongst diesel drag racers, sled pullers, and others who require power gains in excess of 600 lb-ft over stock. Steve sat down with us and asked a semCheck ries of questions to evaluate what we wanted to do with our project. After a few minutes, Steve handed us the keys to his own personal 600hp test rig and said, "Go ahead, take it for a spin." We started giggling the moment we pulled out of Steve's complex. After a downright scary 61/2 miles, we were convinced TTS could give us both the power we wanted and the long-term reliability our donor rig's owner expected. So we left the truck with Steve and headed off to Moab for Easter Jeep Safari.

The stock Duramax fuel in-tank pickup has a flow-restricting, 0.240-inch inner diameter. Due to the fact that all other OE fuel line and connectors on the truck feature no less than a 0.500-inch I.D., the in-tank neck-down is the first obstacle you must overcome to increase power. Without doing so, the fuel system robs the engine of usable power and also negatively impacts injection timing because of cavitation. TTS designed this upgrade so that the pickup line is roughly twice the size of the stock pickup. To complete this modification, you must drop the fuel tank and replace the factory setup with the items shown here. Altogether these upgrades increase fuel flow by more than 140 percent.

Upon our return from Utah, we picked up the newly improved donor truck from TTS. We asked Steve to show us exactly what he did to achieve our power goals. Much to our surprise, it didn't take a whole lot of hard parts to get the power we were after. Shown here is the dual lift-pump kit TTS offers to costumers who want to make up-wards of 600 rear wheel horsepower. This configuration resolves multiple problems associated with the stock GM fuel-delivery system. The kit installs near the fuel tank and drastically improves flow to the CP3 injector pump.