One of the benefits of owning a new Chevrolet or GMC Duramax diesel truck is the towing power and fuel economy these awesome rides tend to deliver. At the heart of this is the Duramax 6.6L engine, which is stuffed with all sorts of Performance enhancements like 16.8:1 compression, a roller camshaft, and an iron block fitted with aluminum heads. Climb behind the wheel, hit the throttle, and you confidently pass traffic, even while towing. But for those looking to add some real driving fun, like nail-you-to-the-seat power, we have some very good news. With a few minutes of work and a couple hundred bucks, you can instantly transform your tow rig into a real hauler!

How's the tune of an additional 100 horses and well over 200 lb-ft of torque to your Duramax sound to you? How's it done? Well, the good folks at Granatelli MotorSports now offer a flash tool they call the Big G, and by following a few simple steps on the plug-in, handheld programmer, you can raise your truck's power in minutes.

To showcase how simple this truly is, we followed along as our friend Tim reprogrammed his '05 Chevy Duramax 2500 truck for more power. You don't have to take our word for it, but you can't deny the before and after chassis dyno numbers. Now keep in mind that the numbers gathered are measured at the rear wheels and take into account the mechanical loss through the drivetrain. The numbers you see on Chevrolet's Web site or get from your local GM dealer are not rear-wheel power numbers, but rather net ratings, taken with all accessories installed and the engine out of the vehicle. In other words, the rear-wheel power numbers will be somewhat lower than what you're used to seeing. But what's important here is the drastic performance increase you can get from your Duramax diesel truck.

Here's a quick list of some of the other features provided by the Big G Flash Tool:

-Idle (+500 rpm/-300 rpm)
-Top-speed limiters
-Rev limiters in any gear
-Shift points based on rpm and mph (automatics only)
-Shift timing and shift pressure (automatics only)
-Cooling fan on/off temperatures.
-Speedometer recalibration for multiple gear ratios
-Speedometer recalibration for multiple tire size changes

Our first baseline test demonstrated how much power the '05 Duramax 6.6L engine delivers to the rear wheels in stock trim. At 2,400 rpm we recorded 415.27 lb-ft, and at 3,100 rpm 218.04 hp. The published net ratings (all accessories mounted and the engine out of the vehicle) from GM are 310 hp at 3,000 rpm and 605 lb-ft at 1,600 rpm, which means that about 92 hp or 32 percent drivetrain loss from the four-wheel drive transfer case and rearend during driving. The Big G Flash Tool (PN 989517-135) costs $339.95 from www.summitracing.com and is designed to fit '01-06 Chevrolet and GMC Duramax diesel trucks.
Baseline Test I
RPMTorqueHP
1,800174.3961.23
1,900177.7564.76
2,000184.0370.21
2,100188.7275.55
2,200194.7481.77
2,300399.98176.37
2,400415.27189.53
2,500410.92195.52
2,600395.42195.83
2,700396.18203.64
2,800382.43203.59
2,900375.25207.20
3,000379.56216.91
3,100369.79218.04
3,200352.00213.64
3,300351.58217.72
For Test II we reprogrammed the tune in the Tow mode and raised the torque figures at 2,400 rpm to 557.76, while the horsepower at 2,800 rpm jumped to 279.02 at the rear tires, which is 390 hp and 807 lb-ft using GM's published net rating. That's a total of 60 hp and 140 lb-ft of torque from the Tow tune alone.
Test II, Tow Tune
RPMTorqueHP
1,800193.5866.59
1,900189.8068.56
2,000196.5374.14
2,100206.4482.33
2,200223.8394.24
2,300537.73236.94
2,400557.76254.73
2,500554.69263.91
2,600545.67270.12
2,700527.62271.12
2,800524.71279.02
2,900471.40260.84
3,000438.79249.92
3,100463.18272.87
3,200445.59269.92
3,300416.84262.65
3,400404.45259.71
3,500348.88229.44
For our final test we selected the Performance tune and again raised the torque numbers at 2,800 rpm to 619.38 and the horsepower at 2,800 rpm to 330.76, surpassing the baseline numbers by 110 hp and 204 lb-ft of torque, making 462 hp and a whopping 897 lb-ft again using GM's net rating. Comparing the Tow tune to the Performance tune yielded an improvement of 50 hp and 60 lb-ft to the tires. If that isn't enough, the Race tune is only a few pushes of the buttons away.
Test III, Performance Tune
RPMTorqueHP
1,800203.5969.87
1,900214.1177.76
2,000216.0682.64
2,100219.4687.57
2,200374.47158.81
2,300550.34242.11
2,400592.55271.48
2,500604.03287.57
2,600611.99303.28
2,700607.69312.01
2,800619.38330.76
2,900586.92324.19
3,000543.37309.12
3,100463.21273.81
3,200358.64217.50
3,300368.07231.21
3,400364.25235.69
3,500346.88229.24
SOURCE
Granatelli Motor Sports
8-05/-486-6644
www.granatellimotorsports.com
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