Prepping A ’13 Duramax for Four-Digit Horsepower
Hurting an engine is an inevitable outcome for many of us suffering from the diesel addiction. It’s a unique conundrum because—in an age where many scoff at the idea of 600 hp, and 700, 800, even 900hp trucks seem to be the norm—it’s hard for any enthusiast to sit back and accept mediocre while the potential exists to turn up the wick and run with the big boys. Many pursue the latter route on stock internals, only to have the hourglass quickly run out. Such was the case for the owner of this ’13 LML Duramax. The urge to make more and more power on the stock bottom end was too hard to resist, and after pushing the factory hardware to more than 800 rwhp, it developed a tick following a nasty burnout. Upon teardown, it was discovered that all eight connecting rods had been bent.

While we hate seeing stock bottom ends give up the ghost, we have to admit that these types of catastrophic failures lead to some of the best engine builds, or perhaps we should call them overbuilds. Turning to the Duramax experts at Illini Outlaw Diesel in San Jose, Illinois, this LML would be reassembled with some of the best aftermarket parts available. A girdle, keyed crankshaft, billet main caps, forged steel connecting rods, fly-cut pistons, alternative firing order camshaft, and ported heads would prep the long block for 1,000hp duty, along with plenty of other upgrades. Read on for a full recap of the ground-up build that readied this LML for “King of the Street” status. DW

1 After surviving everything a set of 60-percent-over injectors, dual CP3s, and compound turbos could dish out for a short period of time, this is what all eight factory LML connecting rods looked like. At a dynotested 808 rwhp, the owner knew he was playing with fire under these circumstances, and that a full-on engine build could be in store at any point in time. That time is now.
2 Once the block’s cylinders had been bored to 0.020-inch over, Mahle Clevite performance main bearings, billet main caps, and ARP main studs were installed, and the main bearing surfaces were align-honed. Align-honing makes each main bearing bore perfectly round, thereby allowing the crankshaft to spin as freely as possible
3 River City Diesel handled the machining of the block and would also balance the rotating assembly. Bobweights (used to simulate the rod and piston combination the engine would utilize), an ATI Super Damper, and a billet flex plate from Sun Coast were used in order to balance the crank. A good balancing job, eliminating torsional vibrations via a quality damper, a matched set of injectors, and quality tuning are all essential in making a crankshaft live in a high-end Duramax build.
4 To rule out the possibility of the factory crank dowel breaking off, the crankshaft was cut for a keyway and fitted with a steel bar (known as “keying the crank”). This is common practice for any Duramax build, as the 5mm dowel that holds the cam gear, oil pump, and balancer in place is known to shear off the snout of the crankshaft in high-horsepower applications. Once the crank and cam get out of time the engine self destructs in short order, so it’s the ultimate insurance policy to have the crank keyed.
5 After first installing the piston cooling nozzles in the block, Illini Outlaw Diesel technician Will Clark added assembly lubricant to the top Mahle Clevite performance main bearings (PN MS-2218H) and installed them on their respective journals. As for clearance, Illini targets the middle ground of bearing clearance specs in its performance engine builds. Erring on the side of things being a tad loose is better than them being too tight, especially when crank flex and main bore distortion is taken into account.
6 Next, Clark carefully installed the crankshaft, checked its end play, and then coated the main journals with a generous amount of assembly lube. From there, ARP main studs were threaded into the block (hand tight) and the supplied Ultra-Torque assembly lubricant was applied to the exposed threads.
7 With the Duramax’s factory main bearing caps (right) known to collapse under high-torque circumstances, a set of billet units from Empire Performance Engineering were called on as suitable replacements (left). Made from 4140 chromoly steel, they vastly increase block rigidity and reduce crankshaft deflection—not to mention they’re noticeably beefier in every way.
8 Installing snugly within the deep skirt block, Clark used a rubber mallet to tap the billet main caps into place. Other key benefits of the Empire billet main caps are that they’re tapped for use with a puller tool (for easy removal) and are designed to incorporate factory oil pickup tubes. We’ll note here that, because a girdle would eventually be bolted to the bottom of the crankcase, the main stud nuts weren’t torqued to spec at this time.
9 The rods of choice for this build were a set of forged steel units from Wagler Competition Products (the same rods that were formerly produced by R&R Racing Products). Of an I-beam design, they weigh in at roughly 1,170 grams apiece, are said to be some of the strongest rods available for the Duramax, and utilize high-strength 7/16- inch ARP 2000 rod bolts.
10 For high-powered, street-driven trucks, the Mahle Motorsports line of pistons is still the main game in town, so sitting atop each connecting rod is one of its 4.075-inch bore forged-aluminum units. They feature 0.075-inch deep valve reliefs, which will compliment the high-lift cam the engine will sport as well as keep high rpm instances less worrisome. A 1.5mm top piston ring offers improved sealing and heat transfer, and the ring lands are hardanodized to reduce wear. The skirts also benefit from a dry film lubricant, which reduces in-cylinder friction.
11 Unlike some of the other piston offerings in the Duramax segment where spiral locks are used, the Mahle Motorsports units utilize traditional snap rings to secure the wrist pin. Here, the number 2 snap ring is being installed (sharp side out).
12 For utmost durability, Mahle Clevite standard size performance rod bearings were used in the build (PN CB-1805H). Incorporating Mahle’s TriMetalTM design, these bearings are said to be capable of withstanding in excess of 1,200 hp.
13 Readying the piston and rod assemblies for installation, Clark dipped each piston in a bucket of fresh 15W-40 motor oil prior to sliding them into their respective cylinders. The top of the cylinder bore was also lightly coated with oil prior to each assembly’s insertion.
14 Using a tapered piston ring compressor from ARP (sized specifically for the 4.075-inch bore being used in the build) made installing each piston and rod assembly a breeze. When it was confirmed that no binding was present, Clark tapped each piston home with a rubber mallet.
15 Once each piston and rod was in position on the crank, Clark prepared the rod cap for installation. After the cap was fitted with the lower Mahle Clevite bearing (which are conveniently labeled upper or lower), the rod bolts were coated with Ultra-Torque assembly lubricant and then handtightened into place.
16 With all piston and rod assemblies (and rod caps) in place on the first bank, the block was rotated 180 degrees and the rod bolts were torqued to spec. The torque spec for the 7/16-inch ARP 2000 bolts was 75 ft-lb.
17 We should note that throughout the assembly process, Clark rotated the crankshaft a handful of times to ensure there were no clearance issues— along with frequently wiping any minor airborne debris off of the engine. He reminded us that you can never be too careful in a high-dollar, high-horsepower build.
18 Next on the to-do list was the installation of the camshaft—a 6480 unit from SoCal Diesel. To reduce stress in the crankshaft’s first rod throw area, this alternative firing order cam effectively changes the firing order from 1-2-7-8-4-5-6-3 (stock) to 1-5-6-3-4-2-7-8. By moving cylinder numbers 3, 1, and 2 away from each other in the firing sequence, alternative firing order cams have greatly improved the amount of extended abuse the crankshaft can withstand in high-torque applications.
19 Even though the keyway on the crankshaft will permanently secure the cam gear in place, the keyway that exists on SoCal’s 6480 camshaft eliminates the factory pin and keeps the cam gear from rotating on the camshaft itself. Once the cam was in place, Clark moved on to installing a fresh Melling oil pump, followed by the reluctor wheel.
20 Because the heads were resurfaced, grade C head gaskets were employed to
maintain proper piston-to-valve clearance. With the grade C gaskets resting
on the cylinder head dowels, Clark began installing a set of ARP’s Custom
Age 625+ head studs.
21 While at Wagler Competition Products’ facility, the factory heads received more than just a simple resurface. A set of Wagler’s beehive valve springs and titanium retainers and keepers were added, along with considerable port work.
22 As measured by Wagler Competition Products, the factory aluminum heads (utilizing the stock diameter 33mm intake and 31mm exhaust valves) can be massaged to flow an additional 60 cfm on the intake side and 50 cfm on the exhaust side. That’s a 33-percent increase in airflow on the intake side. For the owner of this engine, that means less boost will be needed to make big horsepower (i.e., easier on parts).
23 Once all head stud threads were coated in ARP Ultra-Torque assembly lubricant,
Clark thoroughly cleaned the mating surface of the driver-side cylinder
head. Then the head was carefully placed onto the block.
24 With all supplied washers and nuts in place, Clark began torqueing the head stud nuts. In a three-part sequence, the nuts were torqued to 50 ft-lb, then 100 ft-lb, and finally 150 ft-lb. The supplied M8 bolts were torqued to the 25 ft-lb spec.
25 Next it was time for the girdle. Industrial Injection’s Gorilla girdle kit features a ½-inch thick steel girdle, modified lower crankcase and baffle assembly, and the ARP main studs that were previously installed (but not yet tightened when the billet main caps went on). The supplied upper oil pan is machined to clear the girdle. We’ll note that the rear cover must be on the engine in order to install the girdle.
26 As for installing the girdle, the main stud nuts and washers, rear block dowels, and oil pickup tube fasteners were removed first, followed by Clark performing a trial fit to make sure all oil pan bolt and main stud holes lined up perfectly. Then the block’s pan rail was hit with a bead of ACDelco RTV engine sealant and the girdle was set in place.
27 In addition to the main studs guiding the placement of the girdle onto the pan rail, several oil pan bolts were used (and later removed) for added alignment while Clark installed the main stud washers and nuts. The main stud nuts were tightened in three torque sequences, culminating in the required 175 ft-lb final specification from ARP.
28 The oil pickup tube assembly was installed next, followed by the crankshaft being rotated and the clearance checked between the girdle, crankshaft, pickup tube, connecting rods, and oil pump screen. From there, a bead of RTV was applied to the bottom of the girdle and the upper oil pan was installed.
30 With all the hard parts in place, it was starting to look like an engine. The components responsible for major horsepower production would soon follow: 100-percent-over Exergy Performance injectors, dual CP3s, Wagler Competition Products cast-aluminum Street Intake manifold, and a billet S484 over S468 compound turbo arrangement.














Leave a Reply

Your email address will not be published. Required fields are marked *

You May Also Like

The Future Of Diesel

Diesel mechanics are in high demand, but supply is low. Unfortunately, it seems every year we’re reminded of the lack of skilled diesel mechanics in America. Worse yet, the prospects for…


They are the unsung heroes of the truck and tractor pulling world. The equipment operators, the track crew, the worker bees—the people tasked with building the perfect pulling surface, but…

Ford’s First Diesel Pickup Engine

It was the 1970s and people were reeling from the shock of gas prices that had tripled in just a few short years. The effect was profound: a national 55 mph speed limit,…

LB7 Duramax Engine Tech

When introduced in 2001, there were plenty of naysayers worried that the 6.6L Duramax diesel would never hold up to the abuse and life it’d live in a 3/4 and 1-ton truck. As the years…