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Granatelli Big G Flash Tuner - Diesel Power House

Gaining Monster Truck Power With Granatelli's Big G Flash Tuner

Bob Mehlhoff Feb 8, 2006

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.


The Big G Flash Tool simply plugs into the underdash connector. The unit features 64mb memory for fast programming...

...Those leery of making any changes to the factory settings should note these program changes will not void the powertrain warranty...

...Custom tunes and updates are also available online.

The Big G Flash Tool allows towing-load, performance, and race modes to increase power. The backlit screen is designed with adjustable color brightness and contrast.

The installation takes just minutes to complete and requires no computer skills whatsoever.

When we were done we had garnered more than 110 horses...

...and over 200 lb-ft of torque to the wheels. That's big power!

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


Granatelli Motor Sports
Oxnard, CA 93033

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