Machine shops are the backbone of the diesel performance industry. Everything revolves around the process of precision machining when it comes to building an engine that will handle big horsepower and torque. And, because everyone relies on machine shop services at some point, having one in the company stable puts you a step ahead of the game. In order to achieve maximum quality control, Fleece Performance Engineering dove head first into this side of the industry a few years ago when it purchased Freedom Racing Engines in Brownsburg, Indiana. As a result, they’re now able to produce competition-ready Duramax and Cummins mills that live up to the company’s high standards, their customer’s high expectations, and all work (from teardown to dyno-tested) can be performed in-house.

1 Before any machine work took place, the original LBZ crankcase was treated to HardBlok water jacket filler and allowed to cure. The purpose behind filling the water jackets with this cement-based product is to add cylinder wall rigidity and an overall increase in block strength. It’s a very common process in the sled pulling world, especially in classes that mandate a factory-based block be utilized.
2 With new (billet) main caps being used and because the main bearing bores can become egg shaped when using main studs, the main bearing bores were line bored. Line boring aligns all five main bearing bores to a common centerline and ensures that each bore is completely round (reducing drag on the crankshaft). After that, the main bearing bores were finished (and brought to their ideal target diameter) via align honing.
3 Prior to the main bearing surfaces being align-honed, HX series Mahle Clevite main bearings (extra clearance), billet main caps, and ARP main studs were installed (with the studs getting torqued to spec) to simulate the crankshaft being bolted into place.
4 Continuing on with the block’s prep, it was placed in a square fixture (via the crank and cam journals) and decked to ensure the deck surface was perfectly perpendicular to the centerline of the crankshaft and that both banks would be exactly 90 degrees from each other. From there, the cylinders were bored and prepared for honing.
5 During the cylinder honing process, a torque plate was utilized to guarantee each cylinder remained perfectly round, and to mimic the stresses imposed on the cylinder bores. To achieve both a 4.150-inch bore size (note that a 4.055-inch bore is stock) and an ideal cross hatch pattern in each cylinder, several different polishing stones were used.
6 For added strength and block rigidity over what the factory cast main caps offer (the stock units typically fail by collapsing in high horsepower applications), these billet main caps from SoCal Diesel were employed in the build. A general consensus in the Duramax segment dictates that a girdle isn’t necessary at this power level, so long as billet main caps are used.
7 In order to get the crankshaft as close to internally balanced as possible, quite a bit of the crank’s parent material was removed from its front and rear counterweights and replaced with Mallory, a proprietary alloy of tungsten that is more than two times heavier than cast steel. Key benefits of having more internal balance than external include reduced main bearing wear and less flexing of the crank due to harmonics. This is extremely important, as high horsepower Duramax engines are notorious for snapping crankshafts at the number one rod journal due to excessive rpm and the large external counterweight.
8 An ATI Super Damper and SunCoast billet flexplate were incorporated into the balancing process. This image shows how much material was removed from the weight of the ATI damper versus what comes standard on them.
9 Here you can see the 0.120-inch deep keyway being cut in the crank, which is positioned at top dead center (TDC). Keying the crank does away with the 5mm factory dowel pins that are known to shear off in high horsepower applications, causing the crank and cam to get out of time and leading to catastrophic engine failure.
10 This is what the keyed crank looks like after the keyway has been cut and a steel bar welded in place. This process eliminates what is arguably one of the biggest failure points in the Duramax engine.
11 John Benshoof, a former Top Fuel mechanic for Don Schumacher Racing, handled all of the assembly work. Here he makes sure the main bearing clearance is within spec (0.003 to 0.0035-inches). With a filled-block engine slated to see a fair amount of abuse (high boost and big torque), allotting the main bearings a little more clearance (via the HX series Mahle Clevite bearings) is ideal to accommodate possible crank flex and main bore distortion.
12 Once all of the main bearing clearances checked out, the ARP main stud nuts and side bolts were loosened and removed, followed by the billet main caps. Notice that SoCal Diesel’s billet main caps are tapped to work in conjunction with a puller tool, which makes their removal much easier.
13 Benshoof then set the crankshaft into place, checked its end play, and gave it several rotations by hand to ensure there were no clearance issues. Then the billet main caps were reinstalled and inched into place via a rubber mallet
14 Securing the crank and billet main caps for the final time, Benshoof torqued the ARP main studs in three sequences. The first round called for 125 ft-lb, the second required 150 ft-lb, and then the final spec of 175 ft-lb was met. The side main cap bolts were torqued to the recommend 90 ft-lb specification.
15 It should come as no surprise that the proven H-beam design, forged connecting rod from Carrillo got the call for this high horsepower build. These connecting rods are said to be the strongest aftermarket units available for the 6.6L and they’ve been used in countless engines that have churned out well north of 1,500 hp. At roughly 1,090 grams (per rod), they’re also the lightest aftermarket connecting rod available for the Duramax.
16 Checking the rod bearing clearances was next on Benshoof’s list. And after all eight checked out within spec (between 0.003 and 0.0035 inches), he moved on to measuring piston ring gap.
17 Made from 2618 billet aluminum, the pistons used in the build came from Diamond Pistons. To stand up to extreme EGT and cylinder pressures, these pistons are hard-anodized, and the skirts receive a molybdenum coating in order to combat possible damage from side loading and piston rock. Valve reliefs measuring 0.125 inches deep provide high-rpm peace of mind, as the engine will regularly see 4,200 to 4,300 rpm and as much as 5,000 rpm on occasion.
18 Further fortification of the billet-aluminum Diamond pistons comes in the form of the wrist pins. They’re made by Trend Performance from H13 tool steel and feature a Diamond-Like Carbon (DLC) coating for reduced friction. The wrist pins also call for two spiral lock rings per side (as opposed to conventional snap rings).
19 Next, Benshoof fitted each piston with its respective ring set. For less friction (and more horsepower), better oil control, and utmost durability, a gapless second ring from Total Seal was employed on each piston.
20 With the rod bearings bathed in assembly lube and the piston rings hit with a generous amount of Marvel Mystery Oil, Benshoof installed the piston and rod assemblies one at a time. A tapered piston ring compressor sized to the exact diameter of the cylinder bores simplified the process, and each rod was bottomed out on its respective rod journal using a rubber mallet.
21 Once in place, the rod cap and lower bearing were installed. The rod cap was secured by hand-tightening the ARP bolts (eventually they would all be torqued to 75 ft-lb). It’s worth noting that Benshoof double checked that the numbers on both the connecting rod and cap matched before installing them.
22 The last order of business on the bottom end called for installation of the camshaft. The cam of choice for this build was a custom ground, keyed, alternative firing order unit from SoCal Diesel. Called 6480, this cam changes the firing order (1-5-6-3-4-2-7-8 vs. 1-2-7-8-4-5-6-3 stock) in an effort to reduce the amount of stress the crankshaft sees in the first rod throw area (at the intersection of the second main journal).
23 Up top, a set of Wagler Competition Products heads will fasten to the block via ARP Custom Age 625+ head studs. The heads start out as Wagler/Brodix solid aluminum castings (made from A356-grade aluminum), feature no coolant passages, a ductile iron insert for the combustion area, were machined to accept fire rings, and flow an impressive 320 cfm on the intake side and 270 cfm on the exhaust side (at 0.550-inch lift). Stainless steel (0.090-inch) fire rings and custom graphite head gaskets from Wagler Competition will be employed due to the elevated cylinder pressures the engine will see.
24 For optimized flow at low lift, the Wagler Competition heads are fitted with 37mm Stainless steel intake valves (vs. 33 stock), 36mm Inconel exhaust valves (vs. 31mm stock), and also utilize bronze valve guides. A Wagler Competition Spring Kit entails beehive valve springs with a 160ppi seat pressure rating (at an install height of 1.730 inches), and titanium retainers.
25 So, what’s the rest of the puzzle? Getting to the 1,300hp mark will call for a pair of Fleece’s PowerFlo 750 CP3s (10mm pumps), 350% over injectors, EFI Live tuning, a 75mm turbo clipped down to 66mm (to run the 2.6 Class in the Battle Of The Bluegrass series), and a 76mm charger (to run in the Pro Pulling League’s 3.0 Smooth Bore class).

When we stopped by this spring, the Fleece crew was in the process of assembling a Duramax for a sled puller looking to compete in both 2.6 and the newly created 3.0 Smooth Bore class. Knowing it would take roughly 1,300 hp to put their customer in the winner’s circle, a proven hard-part combination was in order. A filled block, billet main caps, Carrillo forged rods, Diamond forged pistons with valve reliefs, a SoCal Diesel cam, and fire-ringed Wagler Competition heads would make the cut, along with a host of other upgrades. Read on to catch a glimpse of what goes into a Duramax spec’d to compete in the upper echelon of diesel truck pulling.DW

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