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A Peek Inside the Duramax L5P

Inside the 6.6L Duramax L5P

John Lehenbauer
Feb 1, 2017
Photographers: John Lehenbauer
General Motors first introduced the 6.6L Duramax V-8 diesel engine for its ’01 Chevrolet and GMC light trucks. GM cooperatively designed and built the engine with Isuzu to replace the 6.5L oil-burner that was discontinued the year prior. This new engine marked a leap forward in the design, technology, and performance of GM’s diesels, as the indirect-injection and two-valves-per-cylinder cast-iron heads of the 6.5L were replaced with a 32-valve, high-pressure common-rail, direct-injection diesel V-8 with aluminum heads.
The Duramax LB7 laid the groundwork for all the GM diesel engines that followed it. Subsequent generations included improvements that yielded more reliability, improved emissions, and more power, but they were essentially the same engine through and through.
Photo 2/65   |   Have you ever looked at illustrations like David Kimble’s rendering of the new 6.6L Duramax L5P V-8 engine and wanted to know more about the parts being depicted? Read on, as we bring you our piece-by-piece inspection of GM’s all-new turbodiesel.
The 6.6L Duramax L5P is an entirely new powerplant. The development of this fifth-generation V-8 is more of a rebirth than an evolution. Every single part, down to the nuts and bolts, is reengineered to be stronger. The only thing it shares with its predecessors is the size of the bore and stroke. GM took all the knowledge gained from the older generations (weak links, trouble spots, design flaws, and so on) and made improvements to make the L5P stronger and more powerful than its forebears. The newest eight-cylinder Duramax produces 445 hp and 910 lb-ft of torque in stock trim, annihilating the 397hp/765–lb-ft performance of the LML engine it replaces.
GM, Ford, and Ram are embroiled in a continuing battle for diesel horsepower and torque supremacy. GM certainly knows the game and has developed the L5P to be a major player in that war. Its robust design will allow the engine to support power increases without worry of compromising its integrity. Getting a Duramax L5P to produce more than 1,000 lb-ft of torque is literally only an ECM reprogram away.
The following photos and information detail the things we learned about GM’s all-new, 6.6L Duramax L5P diesel engine during a two-day complete teardown, performed at Gale Banks Engineering’s Azuza, California, headquarters by lead engine builder Mike Keegan.
Photo 3/65   |   6.6l Duramax L5P Banks Power Wall Emblem

What the L?!

Have you ever wondered where General Motors gets the designations (LBZ, LMM, and son on) for its Duramax diesel engines and what the identifiers actually mean? The big question is, why is there always an “L” at the beginning of an engine code, and what does the rest of it mean?
Let’s start by explaining what the designations are actually called and used for. GM refers to the engine designations as a Regular Production Option (RPO) code. These codes are usually composed of a combination of three alphanumeric characters. The main reason GM uses RPOs is to keep engine and vehicle Bill of Materials (BOM) and service parts lists in order when there is a change made to an engine. Parts for a specific engine will be released against an RPO and model year to guarantee parts are correctly assigned. This is particularly important when a change is made mid-year, like when the LLY took over for the LB7 in the middle of 2004. A secondary RPO can also be assigned in conjunction with the original to guarantee the BOM and parts are assigned properly when there is a significant difference or change made that is associated with the engine (e.g. LLY+MW7, Allison automatic transmission or LLY+ML6, ZF manual transmission).
Every character used in an RPO is there for a reason. They each have meaning to GM. For example: L stands for engines (e.g. LT1, LS3, and so on), M refers to transmissions, G relates to axles, and so on. So, when GM looks at an RPO, it tells a story of sorts about the engine. When a new RPO is assigned, it normally refers to some type of change that was made and the need to keep that engine model’s parts segregated. When significant changes like an EGR and new turbocharger were used on the LB7, the RPO was changed to LLY to signify the change. In the case of the LML, an entire new engine was developed to replace it, hence a new RPO. The only character that has been a constant through all Duramax RPOs is the first letter: “L (engine).” The other two characters have been redefined as changes were made to the engine platform.
Photo 4/65   |   Here is the new Duramax L5P, shown exactly the way it was delivered from General Motors, with lift brackets and plastic red caps included. The only thing missing is the shipping crate.
Photo 5/65   |   6.6l Duramax L5P Engine Front
Photo 6/65   |   6.6l Duramax L5P Engine Left Side
Photo 7/65   |   6.6l Duramax L5P Engine Rear
Photo 8/65   |   6.6l Duramax L5P Engine Top
Photo 9/65   |   This photo offers a close look at the fuel rail, supply lines, return lines, and Denso injectors, key components of the L5P’s new high-pressure fuel system. Just above the fuel rail (to the left of the oil-fill cap) is the new PCV system. The PCV uses a centrifuge to separate oil from the crankcase gases, while the electronically controlled, variable-geometry turbocharger’s boost forces the separated oil back into block. This system ensures the intake-air charge is always clean and oil-free.
Photo 10/65   |   Mike Keegan starts the disassembly process by removing the heat shields on the topside of the engine.
Photo 11/65   |   With the shielding removed from the back of the engine, the turbo-mounted catalytic converter and EGR cooler (positioned at the right of ’charger) are visible. The catalytic converter exits directly into the exhaust downpipe.
Photo 12/65   |   The engine’s new EGR system is larger (exhaust manifold, valves, and cooler) and features a throttle valve that regulates flow and air pressure at the intake manifold.
Photo 13/65   |   The exhaust side of the turbocharger has a large opening that flows directly into the catalytic converter. Both up-pipes have a nice smooth flow, from the exhaust manifolds to the turbo.
Photo 14/65   |   The manifolds’ heat shields are removed to access the glow plugs, sensors, and manifold bolts.
Photo 15/65   |   The thermostat housing and water pump are easily visible once accessory brackets are extracted from the front of the engine.
Photo 16/65   |   Mike removes the turbo to access the injection pump and hard lines.
Photo 17/65   |   With the valve cover and head bolts loosened, Mike removes the cylinder heads.
Photo 18/65   |   6.6l Duramax L5P Right Side Engine Pan Removed
Photo 19/65   |   With the vibration damper gone, an alignment pin at the end of the crankshaft is visible. Although the pin is only used for correctly positioning the balancer, it does not keep the damper from rotating on the crank. A diamond-dust, washer-friction coupler increases friction and also prevents damper slippage.
Photo 20/65   |   Eight oil squirters are designed with notches to provide additional clearance for the connecting rods. They are also able to supply 1 gallon of oil per minute to each piston.
Photo 21/65   |   Mike carefully unbolts all the pistons and rods and removes them from the block.
Photo 22/65   |   Removing the front cover reveals the timing gears and allows access to the camshaft. The rear adapter plate is not only used to bolt the block to a transmission, it also channels oil and coolant to the back of the engine. The final steps of disassembly are removing the main bearing caps and the crankshaft.
Photo 23/65   |   6.6l Duramax L5P Adaptor Plate Removal
Photo 24/65   |   6.6l Duramax L5P Main Bearing Cap Removal
Photo 25/65   |   6.6l Duramax L5P Crankshaft Removal
Photo 26/65   |   This is what the workbench in Gale Banks Engineering’s engine room looks like after disassembling a Duramax L5P engine. The block on the engine stand toward the back of the room is a Duramax LMM we are using for comparison.
Photo 27/65   |   The block on the top is a Duramax LMM, while the one on the bottom is the new L5P. One visible difference between the two blocks is the addition of two M8 cylinder-head bolts at the upper corners of the L5P’s deck. Not visible is the 0.1693-inch (4.30mm) increase in deck height of the new casting.
Photo 28/65   |   6.6l Duramax L5P Engine Block Right Side View
Photo 29/65   |   As you see in the comparative photos, the L5P (bottom) has an increased number of mounting points and ports in the valley of the block. The ports supply oil to the turbo and rear adapter. The assortment of mounting points is used to secure the turbo with heat shield, as well as the oil, coolant, and fuel lines that run through the valley. The high-pressure pump retains the same mounting location at the front of the block.
Photo 30/65   |   6.6l Duramax L5P Engine Block Valley
Photo 31/65   |   Note the differences in the blocks’ castings. The L5P’s redesign yielded a 20 percent increase in strength to enable the block to handle increased cylinder pressure of 180 bar (measurement of atmospheric air pressure). Older Duramax engines operate at 150 bar. The new block is also 9 pounds heavier than our comparison LMM casting. The L5P is made of high-strength, heat-treated cast iron, featuring induction-hardened cylinders to reduce wear in the ring-travel area.
Photo 32/65   |   6.6l Duramax L5P Engine Block Right Side
Photo 33/65   |   The completely redesigned L5P aluminum piston, connecting rod, and wristpin on the left do not have anything in common with their LMM counterparts. A laser is used to melt the tops of the L5P’s pistons, and then the lead-in edge of the bowls are machine-radius’d. Adding the radius helps reduce soot generation.
Photo 34/65   |   There is a definite height difference in the two pistons. The L5P slug is the taller of the two. Its compression height is also increased by 0.1693 inch (4.3mm) to 2.1377 inches (54.3 mm) to accommodate a larger wristpin of 1.4173 inches (36 mm).
Photo 35/65   |   The new piston’s (left) increased mass is also immediately noticeable. The walls are thicker, and there is more contact area for the wristpin. The L5P piston is 7 grams heavier than the LMM.
Photo 36/65   |   The wristpin diameter for L5P pistons is increased to 1.4173 inches (36 mm) from the 1.3582 inches (34.5 mm) of previous Duramax models.
Photo 37/65   |   A lot of engineering and thought was put into the new engine’s connecting rods, which are 20 percent stronger than previous versions to accommodate the powerplant’s increased cylinder pressure. The first difference is the offset bearing cap. This design was used to increase internal clearances as the crank rotates. The rods are powder-cast as single pieces, and then the caps are broken off to ensure proper alignment. The bolts are retained in the cap to ease rod assembly. The material used for the rod bearings is upgraded, and the width of the bearing is increased from 0.9299 inch (23.62mm) to 0.9618 inch (24.43mm).
Photo 38/65   |   6.6l Duramax L5P Rod Bearings
Photo 39/65   |   The new L5P oil pump (left) has 19.6 percent more capacity than its predecessor. The oil-pump gear’s diameter and speed engine remain the same, but the width is increased from 0.510 inch (12.954 mm) to 0.6102 inch (15.5 mm). This increase provides 21 gallons per minute to the engine and turbocharger.
Photo 40/65   |   6.6l Duramax L5P Oil Pumps Back
Photo 41/65   |   6.6l Duramax L5P Oil Pumps Disassembled
Photo 42/65   |   The Denso G4S Gen III solenoid-type injectors (left) are new to the Duramax engine. The top-mounted solenoid and fuel inlet, along with 0.7677-inch (19.5mm) body diameter, make it distinctively different from its counterpart. Denso’s Mini-Sac nozzle provides 830 cc of fuel per minute through seven holes and a 180-degree spray angle. The tip of the nozzle protrudes 0.059 inch (1.5 mm) into the cylinder. The hold-down bracket assembly is redesigned for the new injector.
Photo 43/65   |   Denso’s HP4 is the high-pressure fuel pump (left) that was chosen for the L5P. The Denso is a dramatically different pump than the Bosch unit it sits next to. The new pressurizer uses three high-pressure cylinders, an eccentric drive mechanism, and a 1:1 drive ratio to provide 1.22 cc of discharge per revolution. It also has an integrated fuel flow control valve, a filter screen at the pump inlet, and a single high-pressure outlet. A pump-mounted primer and a temperature sensor were omitted on the new unit. Unlike previous generations that rely on an engine-mounted suction pump and filter for supply, the new system uses a chassis-mounted filter and is fed by an in-tank supply pump that maintains 4-bar pressure throughout the system. The fuel-pressure sensor is also moved away from the engine.
Photo 44/65   |   The lifter and pushrod on the left are the new lighter LS-engine-derived pieces used in the L5P. The LS-style lifter only weighs 138 grams, which is 64 grams lighter than the LMM’s. The lifter has a cold-formed body, an 18-needle roller bearing, and a crowned 0.6998-inch-wide (17.775mm) follower. Even though the L5P pushrod’s (left) length is significantly shorter and the diameter is smaller, it is only 1.3 grams lighter than the LMM (87.5 grams). This is due to the use of stronger, thicker-walled tubing in the rod’s construction.
Photo 45/65   |   The photo on the top shows the L5P’s LS-based pushrods, lifters, and nylon guide, which is a captured lifter design. The bottom photo shows LMM lifters, pushrods, and metal guide assembly.
Photo 46/65   |   6.6l Duramax L5P Push Rods Metal Guide Lifters
Photo 47/65   |   The most significant difference between the L5P camshaft (left) and the LMM cam is the width of their lobes.
Photo 48/65   |   The intake runners in L5P cylinder heads are designed for improved airflow and volume.
Photo 49/65   |   Larger exhaust ports (top) give L5P heads the flow that’s necessary for supporting the improved volume on the intake side.
Photo 50/65   |   There are noticeable differences in the new cylinder head (top) and LMM. A big improvement in the L5P’s head is the addition of two bolts in the upper corners of the head, making a total of six. Valve sizes remain the same in the new head. The valves are nitrided (a process that case-hardens the surface) and then polished.
Photo 51/65   |   6.6l Duramax L5P Heads Valve Seats
Photo 52/65   |   6.6l Duramax L5P Heads End View
Photo 53/65   |   The crankshaft (top) for the new Duramax is a distinct design. The main journals retain the same diameter (3.1464 inches/79.92 mm) but use wider bearings. Main bearings for journals 1 thru 4 are now .9566 inch wide (24.3 mm), which is an increase of 0.1417 inch (3.6 mm) over the old bearings. The Number 5 main (thrust) bearing saw a bigger increase in size, from .8149 inch (20.7 mm) to 1.019 inch (25.9 mm). The rod-bearing journal diameter is increased from 2.4764 inches (62.902 mm) to 2.6771 inches (68 mm). The crank-position tone ring is now located internally on the engine, at the back of the crank for more precise timing. The back of the crank has less distortion/deflection than at the damper end.
Photo 54/65   |   A new, larger turbo features a billet compressor wheel and an electronic controller for reduced lag.
Photo 55/65   |   6.6l Duramax L5P Rear Turbos
Photo 56/65   |   6.6l Duramax L5P Side Turbos
Photo 57/65   |   The L5P’s redesigned water pump (left) has increased flow to meet the HVAC system’s requirement of 340 lpm. The pump is able to achieve the improved flow thanks to a refined impeller and a smaller drive-gear tooth count (41 to 36 teeth), which creates a 1.19:1 pump ratio.
Photo 58/65   |   6.6l Duramax L5P Water Pumps Back
Photo 59/65   |   6.6l Duramax L5P Water Pumps Disassembled
Photo 60/65   |   6.6l Duramax L5P Water Pump Impellers
Photo 61/65   |   The new oil cooler/heat exchanger (right) is larger to accommodate the increase in coolant and oil flow. The cooler has three additional veins to handle more oil and to better disperse heat.
Photo 62/65   |   These bottom views of the upper oil pans present differences in their design. With the new piece (bottom), the oil-pickup tube is incorporated into the pan, instead of passing through it. The mounting surfaces indicate the size difference of the associated lower oil pans.
Photo 63/65   |   6.6l Duramax L5P L5p Oil Pan Bottom View
Photo 64/65   |   Viewing the topside of the oil pans clarifies how the L5P pan (bottom) is designed with a completely integrated windage tray to reduce oil aeration that could damage the engine.
Photo 65/65   |   6.6l Duramax L5P L5p Oil Pan Top View

Sources

Gale Banks Engineering
Azusa, CA 91702
800-398-9256
www.bankspower.com

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