Normally, when issues like damage and high mileage make replacing the cylinder heads on a 6.6L Duramax diesel engine necessary, most people use rebuilt stock heads. This has been the standard practice because replacement aftermarket heads—especially aluminum—simply aren't available in massive quantities.
Enthusiasts in search of more power are in a similar situation, relying on reconditioned factory heads that are sometimes ported and upgraded with aftermarket valvetrain hardware. Edelbrock, a company well known for producing performance cylinder heads for gas-powered engines, has changed that in a big way.
With the release of the 6.6L Duramax cylinder head, Edelbrock becomes one of only a few aftermarket companies to offer performance-oriented cylinder heads for diesel engines. This direct-bolt-on aluminum head is a great alternative for replacing worn-out heads and increasing performance and durability.
| The first order of business is to put the truck on the dyno and get a baseline that will be used to compare the before and after effects of Edelbrock's 6.6L Duramax cylinder head installation. The engine made 523 hp and 940 lb-ft of torque.
Designed to be ready to run out of the box, the Edelbrock heads are compatible with all stock Duramax valvetrain components, along with valve covers, the water crossover, injectors, and glow plugs. The heads are made from A356 aluminum castings that are heat- and pressure-treated to reduce porosity in order to increase the strength and fatigue properties of the material. Created to be more than just replacement heads, the intake and exhaust runners are engineered to optimize the flow and swirl of incoming and exiting air. Further enhancing the heads is extra material in the deck for increased strength and in the ports to allow for custom porting.
Something that makes these heads particularly appealing to many is the fact that they are CARB legal, meaning they can simply be bolted on as replacements for those old, damaged, or high-mileage stock units without any emissions worries.
Hearing a well-known company like Edelbrock has developed a new cylinder head for diesel engines definitely piqued our interest. So, as soon as we could get our hands on a set of the Duramax heads, we got in touch with our friends at FTK Diesel in Boardman, Ohio, to map out a plan to install them and evaluate their effect on a late-model Duramax engine.
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Ray McClelland Jr., the proprietor of FTK Diesel, owns the '14 GMC Sierra 3500HD daily driver/tow rig we selected for this project. It was chosen because the engine has never been taken apart, and the modifications it has are fairly common for 6.6L Duramax LML engines. The updates include a Tater Built Turbo Chargers & Machining modified stock turbocharger, a 12mm CP3 injection pump, a Fuelab Velocity 100-gph lift pump (with FTK Diesel install kit), and a street tune. Backing the engine is a stock transmission with custom tuning to help it hold up to more than 500 hp.
To get a true feeling for what the new Edelbrock diesel cylinder heads can do, we decided to also upgrade the stock intake and exhaust manifolds, as well as the up-pipes during the installation. A Wehrli Custom Fabrication '11-to-'16 Duramax LML High Flow Intake Bundle Kit and a PPE Ceramic-Coated High-Flow Exhaust Manifolds and Up-Pipes Kit were enlisted to allow the engine to breathe.
The first order of business before FTK Diesel's Technician David Schiel turns a wrench is to put the truck on the dyno to get a performance baseline. For projects like this, having before and after dyno numbers gives us data that qualifies exactly what the heads are capable of doing.
| FTK Diesel technician David Schiel starts the process by removing the front fenderwell liners and the radiator/intercooler cowling cover to gain better access to the engine bay.
| After extracting the batteries, David disconnects the sensors and removes the air intake and airbox.
| The fan and clutch assembly are taken out, along with the cowling, giving David a clear shot to the front of the engine.
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| After the front of the engine is dismantled, the top of the engine is deconstructed.
Before removing the turbocharger, the downpipe and up-pipes have to come off. The same turbo will be going back in, but the pipes are being replaced with better flowing PPE and Wehrli Custom Fabrication tubing.
| With the turbo out of the valley, the remaining lines, fitting, and other components are removed.
| David takes off the exhaust manifolds. These too are being discarded for better flowing PPE ceramic-coated pipes.
The injectors, fuel rail, and corresponding lines are removed from the heads, as are the valve covers, rocker shaft, and pushrods. David then unbolts and lifts the heads of the engine.
| The old heads are set on the floor with the intake manifolds still intact. The manifolds will be cleaned before being installed on the new heads.
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| The Edelbrock 6.6L Duramax cylinder heads are universal; they can be used on the left or right bank of the engine. What determines which side they are used on is how the included freeze plugs are configured for the cooling system and where the studs are installed. David uses the original heads as a template to index the new heads as left and right. The Edelbrock 6.6L Duramax cylinder heads are universal; they can be used on the left or right bank of the engine. What determines which side they are used on is how the included freeze plugs are configured for the cooling system and where the studs are installed. David uses the original heads as a template to index the new heads as left and right.
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| Before installing the new heads and gaskets, the block's mounting surface is cleaned of any old gasket material.
Merchant Automotive sent us a Duramax Head Gasket Kit (LML) that includes all the gaskets, seals, glow plugs, head studs (ARP), and miscellaneous items needed to do the top end of a Duramax engine. It also shipped a Heavy-Duty Pushrod Kit.
With the block cleaned and inspected, David begins the reassembly process. After the head is set in position, the ARP head studs are installed and tightened by hand.
| Before installing the valvetrain, the valve tappets are coated in Red Line Synthetic Oil Assembly Lube to guarantee no metal-to-metal contact happens before engine oil reaches the heads.
New Merchant Automotive heavy-duty pushrods are dropped into position, then the cups are filled with assembly lube before the rockers are installed. With the rocker shaft properly torqued, the engine is rotated in increments and the valve lash is adjusted.
| David bolts the intake manifolds, valve covers, and fuel rail onto the heads.
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| The original injectors are reused, but they are fitted with new gaskets and seals from Merchant Automotive before being installed. Once in place, the injector hold-down bolts are torqued to specification.
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The job of correctly installing the lines, brackets, and accessories takes time, but once it is completed, David maneuvers the turbocharger into place in the valley.
Here is a side-by-side comparison of the stock exhaust manifolds and the PPE High Flow units. With most of the engine reassembled and the turbo in position, installing the exhaust manifolds and up-pipes is the new focus. Once the manifolds are bolted into position, the up-pipes are attached.
| This is a look at the components that comprise the Wehrli Custom Fabrication Duramax LML High Flow Intake Bundle Kit. We ordered the tubes in Illusion Cherry. The kit includes all the boots, clamps, and hardware needed for installation.
| Sensors are installed on the intake and Y-bridge.
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| David installs the Y-bridge and charge pipes. He leaves the bubble wrap on the tubes to protect them from being scratched.
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Adding the downpipe, coolant tank, air filter, and upper coolant pipe finishes up the Intake Bundle installation.
The last order of business before firing the engine is to top off the fluids. We used a Karen's Transport Duramax Cat oil-filter adapter, which enables us to install a larger Cat filter. Then the engine is filled with Red Line Synthetic Oil 15W-40 diesel engine oil.
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| After a testdrive to make sure everything is working properly, the GMC is strapped back down on the dyno to see if the new Edelbrock heads made a difference in performance.
| In the initial dyno run, the truck made 523 hp and 940 lb-ft of torque, with the peak power coming on higher in the rpm range. After the installation, the power made a slight jump to 573 hp (50hp gain), while the torque made a much bigger gain to 1,184 lb-ft (an additional 244 lb-ft). A significant difference seen between the original and Edelbrock heads is where the peak torque comes in—at a much lower rpm with the Edelbrock units.
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A Side-by-Side Comparison of Duramax Heads
We did a visual comparison of the new Edelbrock '11-to-'16 Duramax cylinder heads and stock pieces that were taken off. There are some definite differences in the design of the castings. The extra material in the Edelbrock heads (for custom porting and increased strength) is very noticeable. Take a look at the following images (the Edelbrock are the clean ones).
| Looking inside the exhaust port shows the difference between Edelbrock's (right) design and the original Duramax head (left).
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Since installing the Edelbrock Duramax diesel cylinder heads, Ray has had some time to really drive the '14 GMC Sierra 3500HD and give us some insight into how the engine feels. "As far as the driveability and torque gains, it feels like a completely different truck," he says. "Pulling a trailer seems even more effortless, with less downshifting and lower EGT when going up a grade. The heads even drastically changed the sound of the engine and gave it a lot smoother idle. Overall, I am extremely impressed with the heads."