WHAT MAKES THE DURAMAX SO GREAT

AND THE AFTERMARKET PARTS THAT MAKE IT EVEN BETTER

It’s hard to say where GM’S heavy-duty pickups would be today if the Duramax had never been born. Back in the late 90s, the auto giant was desperate to get its hands on more than the dismal 3-percent slice it held in the domestic diesel truck pie. But after the 5.7L debacle of the late 70s and early 80s, and in knowing how dated and underpowered the 6.2L and 6.5L platforms were, GM knew its next oil-burning venture had to be a homerun. Turning to Isuzu, the Japanese vehicle and engine manufacturer it had been a longtime stakeholder in, the DMAX Ltd. joint venture was formed. Isuzu would handle the engine’s base design while GM would handle integration into its vehicles.

As proof that GM and Isuzu got it close to perfect right out of the gate, the 6.6L’s basic architecture has remained the same for 20 years now. It still sports a deep-skirt, cast-iron block with induction-hardened cylinders, fourvalve aluminum heads with six head bolts per cylinder, and clean-burning, quiet operating, common-rail injection. For a look at what puts the “dura” (for durable) in the Duramax name, we’ll examine the OEM hard-parts that make it possible in the following pages. Then, building upon an already-stout foundation, we’ll explore the time-tested aftermarket components that make GM’S 6.6L V-8 nearly indestructible.

There is nothing glamorous about a block cast from gray iron, but (in addition to pleasing the bean counters at GM) the same overall design and material has proven highly durable in the case of the Duramax. It typically takes more than 1,000 hp to find the structural weak points in the cylinder walls, but you need a vastly upgraded rotating assembly before you get anywhere close to that number. Throughout the Duramax’s production run, key areas of the casting have been beefed up, but the same 4.055-inch bore and 3.897-inch stroke has been retained. It’s also worth noting that the Duramax’s 90-degree layout makes for a compact overall package, which eased the integration process into GM’S trucks and vans.