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