The basic Duramax engine hasn’t change much since GM put it that in the first HD Silverado and sierre back in 2001. It’s good solid engine performs well and can last for hundreds of thousands of miles at or near stock power levels. But for sled pullers, racers and hardcore diesel performance enthusiasts that want more out of the Duramax platform, the engine’s internals need to be reworked to reliably make more power and push the performance limits. Jeremy Wagler and his team at Wagler Competition Products in Odin, Indiana, have been at the forefront of pushing the Duramax performance envelope for years now since launching their first aftermarket performance cylinder head in 2013.

The neutral-balanced rotating assembly is the heart of the WCP Race Series engine. The kit is available to purchase so you can build your own engine—or you can have the team at Wagler build the engine for you.
Wagler internally balances the crankshafts in-house.
After the factory GM Duramax block completes its tour of the Wagler machine shop, Steven Fuhrman dresses it up with a fresh coat of paint.
The Wagler crew does not mass-produce their engines; they are each hand-assembled in the engine room. As you can see, most of the internal parts are laid out on the counter waiting to be put into the freshly machined Duramax block.
After installing and lubricating the lower crank bearings, Fuhrman gently unites the Callies crank with the Duramax block.
Then he installs a set of ARP assembly studs and the WCP billet main caps before verifying the proper bearing clearance on the fully torqued main caps.
While Fuhrman was installing the crank, Jeremy Wagler joined the WCP rods to the Ross pistons.
Next, Fuhrman flipped the block over and lubricated the cylinder bores and pistons before slipping them into their new home in the Duramax engine block.
After all the piston and rod assemblies are installed in the block, Fuhrman verifies the clearances and then torques the ARP rod bolts on each of the eight rods.
Rotating the engine to a vertical position makes it easier for Fuhrman to slip the lubricated WCP camshaft into the block.
The 2-inch-thick WCP billet aluminum front and rear covers are installed next.
Working on the bottom side of the engine again, Fuhrman removes the assembly studs and replaces them with a set of longer studs to fit the 1-inch-thick race girdle. Fuhrman then installs the WCP billet steel girdle, torqueing all the ARP nuts and bolts properly before continuing on.
To wrap up the bottom of the Duramax build he installs the billet aluminum dry sump oil pan before flipping the engine back over to finish the top end of the build.
Wagler hand-blends the CNC porting on the X Series Competition cylinder heads for maximum airflow potential.
After the heads are assembled with the oversize valves, beehive valve springs, and titanium retainers, Fuhrman installs a head to verify piston-to-valve clearance with a test gasket, then installs both heads one more time with new gaskets before buttoning them up with ARP head studs.
The factory lifters take an oil bath before Furman installs them and the WCP/Trend pushrods and Wagler billet roller-tip rocker arms and sets the valve lash on each rocker.

In addition to their extensive cylinder head work, the team at WCP has expanded its facilities and capabilities so the company now offers complete Duramax neutral-balanced rotating assemblies, complete engine builds, forged connecting rods, assembled short blocks and more.


After the 2016 Wagler Diesel Competition in Elnora, Ind., we were able to hang out at the WCP shop for a few days and follow along with a Duramax engine build that is expected to produce well over 2,000 horsepower for a new drag race vehicle that’s in the works. Like their other engines, this build starts with a factory GM block that is cleaned, checked and machined in-house to WCP specifications. Each block is honed to the desired cylinder bore, then decked and line-bored before new bearings are installed. To help seal in the combustion charge under high-boost and high-rpm operation, the block is machined for fire rings to work with the Victor Reinz head gasket set.


The WCP Race engine is built with an internally balanced Callies Performance Products billet crankshaft captured by Wagler billet main caps with ARP studs and HX Race bearings. The crank swings a set of WCP Hemi wrist pin connecting rods and Ross Racing pistons. The pistons are secured to the rods with Trend Performance Top Fuel Hemi wrist pins and dual spiral clips, while Total Seal rings are used to seal in the combustion pressure. Since the complete rotating assembly is internally balanced, a zero-balance Suncoast flexplate is used on the tail end of the crank with a WCP/ATI Performance Products damper installed on the front to handle harmonic vibrations. High performance ARP bolts and studs are used throughout the engine assembly to ensure that it all holds together well. With the stock Duramax 3.9-inch stroke and a 4.100-inch cylinder bore, which allows the use of larger 35 and 36mm valves (compared to 31 and 33mm stock), the engine will have about 412 cubic inches of displacement, effectively making it a 6.8L Duramax.


Topping the WCP Race short block you will find a set of second-generation Wagler Competition X Series cylinder heads. The raw material is sourced from a new foundry that delivers improved metallurgy, leading to improvements in the head construction. In addition to CNC porting and hand-blending, the heads feature oversized valves for more airflow in and out of the cylinder to make more power. The valves are actuated by an alternate-fire WCP camshaft, stock GM roller lifters, WCP/Trend Performance chromoly pushrods, and Wagler billet roller-tip rocker arms. WCP Competition beehive valve springs and titanium retainers control the valves, while massive machined billet aluminum valve covers with sight windows on top are used to cap off and contain the valvetrain and S&S Diesel Motorsport fuel injector assemblies.


Additionally, the block is strengthened with a full billet steel 1-inch Wagler Race Girdle that ties into machined 2-inch aluminum front and rear plates, as well as the pan rails on the block. For better oiling and less required oil pan depth, the engine also uses a billet aluminum dry sump oil pan along with a dry sump pump. The machined front cover also accepts the WCP direct-drive, triple-CP3 mounting kit to drive all three high-pressure fuel pumps directly from the cam gear rather than a belt drive as they are with other kits. In addition to a very large set of Pro Mod Precision Turbo compound turbos, this engine was originally planned to be topped by the Wagler airto- water intercooler manifold. But to save weight and complexity they decided that it will be topped with the Wagler billet intake manifold plumbed with multiple nitrous spray bars and enough laughing gas to supply a dentist office for months.

Then the high-flow S&S Diesel Motorsport fuel injectors can be installed in the heads.
Billet fuel rails and matched fuel lines link the injectors together with everything contained under the oversized billet aluminum WCP valve covers.
To make massive amounts of horsepower massive amounts of fuel are needed, so this engine will be running a trio of S&S CP3 pumps to keep up with the high-pressure demands. The mounting plate for the CP3 pumps slides right into the front cover.
The manifold runners are port-matched to the intake ports on the cylinder head, allowing air to freely enter the combustion chambers past the oversized intake valves.
While “Racer X” was originally going to use a water-to-air intercooler sandwiched between the top and plenum of the intake, he opted to spray the engine with a boatload of nitrous oxide with a spray-bar system installed in the intercooler’s place and a bunch of NX solenoids on each side of the intake.

The Wagler crew built this particular Duramax engine for a high-profile racer who plans to install the engine in a new vehicle that’s being built, but who also wants to remain anonymous until the new racer is finished. Once it’s done, we will line it up in our Canon viewfinder and bring you a full feature on the top-secret build. In the meantime, follow along over the next few pages for an overview of Steven Fuhrman building this 2,000+hp Duramax engine that will power the new creation.DW

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