There’s no doubt about it, we’re living in the age of easy horsepower. And perhaps no one knows that better than owners of the tried-and-true Duramax. The LBZ and LMM versions of GM’s common-rail V-8 are known to handle as much as 250 more horsepower than stock without upgrading the valvetrain, injectors, or even adding head studs. Unfortunately, the rite of passage that allows the Duramax-powered trucks to get that power to the ground, reliably, requires a built Allison transmission.
| project Street Max Part 1 chevy On Dyno
Throughout the last 10 years, Sun Coast Converters has invested much of its time in the Allison 1000. Two of its current rebuild kits, coined the GMax 5-pac and GMax 6-pac (5 for five-speed Allisons and 6 for the six-speed version), are among its most popular products. The complete drop-in kit effectively bulletproofs the Allison’s internals, allows enthusiasts peace of mind in pursuing their 600 or 700hp goals, and has become the industry standard for reliability, durability, and performance.
| Sun Coast’s complete GMax 6-pac kit for the six-speed Allison comes with everything a transmission builder needs to tackle the job. Even a complete paper and rubber gasket set, spin-on filter, pan filter, and its Filter Loc (for the pan filter) is included.
We recently got our hands on an LBZ-equipped ’06 GMC Sierra 2500HD and had Flynn’s Shop in Alexander, Illinois, install one of Sun Coast’s GMax 6-pacs and a 1058 torque converter. Then we took the truck to Randall’s Performance and Accessory’s dyno in Gladstone, Illinois, for some baseline power numbers. Stay tuned, as next month we’ll see what an all-out, EFILive-created tune can add to the equation. After that, we’ll clean up our hot tuning (and add even more horsepower) with a popular aftermarket turbo. Our goal is to show you how to build the ultimate street-driven Duramax without having to tear into the long-block.
| Chad Flynn of Flynn’s Shop performed the transmission build. According to him, rebuilding an Allison is a meticulous process—and one that takes time to do correctly. From disassembling the transmission’s modular sections and the factory internals to modifying the valvebody to reinstalling every component in order, it’s very time consuming—and one small mistake can lead to a transmission that fails prematurely.
LBZ Test Mule
Truck Year & Make: 2006 GMC
Model: Sierra 2500HD
Configuration: Four-door, shortbed
Tires: 35x12.50R20 Toyo Open Country M/T
Wheels: 20x10 BMF Novakane
Ring and Pinion: 3.73
Current Modifications
Air Intake: K&N with Amsoil dry filter
Exhaust: 4-inch MagnaFlow single exit (stock downpipe)
Fuel System: AirDog 100-gph
Transmission: Sun Coast GMax 6-pac, 1058 converter
Future Modifications
EFILive tuning
EGR block-off
Fuel rail shim
Head studs
Aftermarket downpipe
Aftermarket turbo
Parts List (labor not included):
Part:
Vendor:
Price:
GMax 6-pac
Sun Coast
$1,624
1058 torque converter
Sun Coast
$1,695
Total Price
$3,319
