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2002 Chevrolet Silverado 2500 Duramax Diesel - Pulltoy

Clint Cannon Fires Off A Big-Caliber Sled Puller

Photography by Steve Temple

Remember when you were a kid, dragging a sled up a hill for a wild downhill ride in the snow? Well, what if the fun part was pulling the sled instead? That's the case with Clint Cannon's '02 Chevy 2500 HD 4x4. Light the fuse on this juggernaut, and it's virtually unstoppable, with 970 horses straining at the reins, pumping furiously at more than 5,000 rpm. Of course, more important for the task at hand is the amount of twisting force on tap.

Got torque? Yeah, in spades. The twin-turbo Duramax delivers an astounding 1,781 lb-ft of torque. That's enough to drag a 43,000-pound sled the length of a football field and spike the ball in the end zone too. And when it's not towing, this rip-roarin' rig cuts and runs through the quarter-mile in 11.4 seconds at 119 mph.

Just how did Cannon load up his pickup with so much firepower? Well, it helps that he's the owner and founder of ATS, a company that makes all sorts of diesel drivetrain upgrades, so he has access to the full resources of his shop and can pick all the needed components right off the shelf. And Cannon's truck serves as a test bed of sorts for his company's products (though we suspect that he also really enjoys dropping the hammer too).

Getting the LB7 6.6L Duramax to produce such a prodigious output is no simple task, however. A tremendous amount of testing and innovation went into this rig. And it's not merely about mondo power either, because an equal amount of engineering went into the chassis setup so the truck works smarter, not just harder.

Starting with the engine block, the innards needed to be both stronger and lighter to handle twin turbos that boost intake pressures to more than 80 psi. About 10 pounds of material was removed from the crankshaft alone, which then had to be shot-peened and cryogenically treated. Also, the counterweights were knife-edged for reduced resistance at high revs, and the entire rotating mass is precision-balanced. Fitted to the billet connecting rods are low-compression pistons (15:1 instead of the stock 17:1).

In addition to porting, the heads have oversized custom valves and springs with titanium keepers and retainers. The high-lift roller camshaft was custom-ground to ATS specs. Keeping the engine from tearing itself apart required 240,000-psi head studs and main bearing studs.

The turbocharger pair is an ATS Aurora Compound Turbo System. For quicker spool-up on the low end of the powerband, there's an Aurora 5000, and a prototype turbo handles the midrange and above. A 2-inch, high-flow wastegate with regulated balance keeps the boost and backpressure in concert. The boost control module controls the wastegate to elevate pressure and also backpressure to get air out of the engine. A fine balance between these two variables is required, with the backpressure slightly lower if possible.

"Getting the two to work together is the tricky part," Cannon admits. "Overlapping two turbos is a real science, since they're so finicky. You have to factor together the diameters of the turbine and compressor wheels, the sizes of turbine housings, and the trim or angle on the vanes." Orchestrating all these variables requires a lot of head-scratching and dyno time-along with some simple trial and error.

Feeding the turbos plenty of air is essential as well. An Arc Flow Intake with 3.5-inch ID supplies fresh oxygen, and a custom stainless-steel vertical exhaust system blows the waste gasses skyward. An ATS water injection system keeps the EGT below 1,000 degrees Fahrenheit, even under full load.

On the fuel side of the equation, a dual Bosch CP3 injection pump system maintains a rail pressure of 28,000 psi (versus 17,000 stock) while it pumps out about twice as much fuel. Custom hardware had to be fabricated for the secondary pump. The Stage 5 Injectors can handle four times as much volume, and twin high-flow FASS lift pumps keep the air out of the fuel.

Coordinating the flow of air and fuel is an ATS E-Power Custom Tuning module that controls a number of variables such as ignition timing, pulse width, and injector duration. Interestingly, instead of using large single pulses for each combustion cycle, the injectors fire in a staccato or machine-gun style in order to ensure smaller droplets that burn better.

In addition, two CP3 pump controllers are needed to keep the dual fuel pumps working in harmony. Cannon says this ATS unit splits the stock electrical signal and reduces it in order to operate the two pumps.

Absorbing the engine's flood of power is a custom, SFI-approved billet flexplate that mates the engine to the ATS Five Star Viskus Clutch Drive torque converter and Extreme Allison LCT-1000 transmission. This automatic tranny is designed to handle as much as 1,300 hp. Other driveline mods include a Co-Pilot Electronic Transmission Controller and extreme-duty input and output shafts. A deeper aluminum pan holds five additional quarts of fluid.

Crossbolts in the exhaust keep the turbine wheel from exiting the exhaust system if the turbo explodes. That's also why the truck also has vertical stacks-it's not just for looks-they keep any engine debris from flying into the spectator stands. As noted above, a sled puller needs more than just tons of torque. Figuring out the correct geometry of the suspension is critical as well. To give the truck maximum leverage and shift weight to the front wheels, Cannon modified the chassis in several areas.

The custom-designed front suspension allows the CV joints to have proper alignment, so they're straighter with a minimum of side load. Also, the tie rods are in a straight line to put max power to the ground. Traction bars transfer power directly to the center of the frame, and an electronic locker is engaged in the front differential during competition.

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