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.
Upgrades, Part 3
Snow Performance is a trusted name in the diesel performance aftermarket because the company's owner, Matt Snow, insists on building a high-quality product that provides consumers with an excellent horsepower gain per dollar spent. We like Snow Performance water methanol kits because they allow end users added safety in regards to exhaust-gas temperatures. The MPG-Max system is the latest kit from Snow Performance. This particular system is designed to inject a mixture of water and methanol at a preset turbo pressure or EGT set point. It also allows for a smaller amount of water and methanol to be injected at lower rpm levels for additional fuel economy gains. When the mixture enters the combustion chamber, the effects are cooler EGTs as well as added power. The total effect is determined by injection rate and percentage of methanol used in the solution. We don't plan to use greater than 15 percent methanol by volume because we're mainly after the EGT cooling effect of the product. However, even with just pure water, the Snow Performance kit can provide performance gains in the neighborhood of 25 to 30 hp. The total cooling effect can drop EGTs by up to 250 degrees as well.
We asked the good folks at Off Road Unlimited (ORU) in Burbank, California, to help us with the installation process. While they hadn't ever installed one of these systems before, they did comment on how complete the system was and how nice it was that everything needed, including flex-hose and fittings, were all included in the kit. Here you can see the 7-gallon reservoir ORU's guys installed in the bed. Snow Performance offers other tank options for those who don't want to hinder cargo capacity. The water/methanol fluid is available directly from Snow Performance or you can simply use any windshield wiper fluid that has methanol listed in the ingredients.
What About Reliability?
Diesel engines found in Duramax trucks have a built-in robustness that allows end users to increase horsepower and torque without sacrificing longevity. However, this is only true to a point. We questioned Steve Cole about our truck's power output, and whether or not we needed to express concern about reliability in this story. His response concluded with, "It all depends on how you drive it." With that being said, we must warn readers that the Duramax engine will likely stay alive for a good long time at 480 hp, though proper judgment should always be used when pulling heavy loads or while accelerating up long steep grades. Anything over 480 hp is pushing the limits of the design of the engine. The hot exhaust-gas temperatures generated by the additional fuel burning can cause pistons to melt, gaskets to fail, and damage to other engine internals. Upgrades like the ones we performed in this story are designed for those of us who don't mind sacri- ficing critical built-in safeguards for the ability to spank challengers at the track. Please realize these modifications are not recommended for emissions-regulated vehicles and are in no way going to increase engine or drivetrain life. The bottom line: The higher the horsepower, the less likely it's going to last 100,000 miles.
The Cost
We get reader requests all the time asking us to list prices of tech projects like this. So this time around we kept a running total to show you approximately how much green it would take to get it done.
