Dual valve springs with Titanium retainers provide the proper spring rate and seat pressure for the kind of elevated rpm and boost levels the engine will see. Also notice the Dirty Hooker Diesel billet-aluminum coolant block-off plate behind the passenger side head, which was installed to rule out the possibility of the common coolant leak occurring at the rear engine cover.

The Inner Workings of An LMM Built to Live at High-RPM

We see a lot of engines go together here at Diesel World, but occasionally we’re able to sit in on a high-horsepower build that breaks the mold. After playing a key role in keeping as many as seven pulling trucks operational during the summer, Kevin Dermody of Dermody Diesel didn’t settle in for a long winter’s nap once the weather in his native Illinois turned cold. Instead, he found himself busy indoors, piecing together a fairly unique combination of parts for a power-hungry Duramax owner. It wouldn’t be a big bore engine nor a stroker, but rather a de-stroked LMM designed to live at high rpm.

Callies Ultra Billet crankshaft
At the heart of the build, you’ll find a Callies Ultra Billet crankshaft with a custom, 3.750-inch stroke (vs. 3.897-inch stock) that was internally balanced at Wagler Competition Products. Callies machines the crank from triple heat-treated 4330v steel before being treated to the company’s Perma-Case nitriding process (for surface hardening). Compared with the factory forged steel crankshaft from GM, the rod journals are narrower (2.165 inches in width) for improved strength.
ARP main studs
Designed and intended to be run upstairs, the short-stroke engine is void of a girdle or billet main caps, but does employ ARP main studs. Made from 8740 Chromoly steel, ARP’s main studs have a 200,000-psi tensile strength rating. Prior to the engine’s assembly, the entire rotating assembly (complete with an SFI-approved Fluidampr harmonic balancer and Sun Coast Performance zero balance flex plate) was internally balanced at Wagler Competition Products. All of the machining (including line boring of the main bearing bores) took place at Wagler’s Odon, Indiana facility as well.

Having been around big bore and stroker versions of the 6.6L in the past, Dermody was accustomed to sizing turbochargers for stock or increased displacement engines. Needless to say, turbo selection presented a new challenge for a high-rpm screamer. First and foremost, he wanted chargers that wouldn’t run out of steam at 3,500 rpm. However, he needed them to be reasonably responsive at low rpm. Beyond turbo selection, Dermody would enlist the help of some of the biggest names in the industry, with companies like Wagler Competition Products, Diesel Technology Source, S&S Diesel Motorsport, and HSP Diesel all coming onboard.

For a look at the complete build sheet behind this short-stroke, 390 ci Duramax’s somewhat unorthodox route to making power, keep reading.

Wagler Competiton - forged-steel connecting rods from Wagler
The Ultra Billet crank swings a set of forged-steel connecting rods from Wagler, which accommodate a Trend Performance Hemi-style wrist pin on the small end. Forged from 4340, the I-beam style rods are shot-peened for enhanced strength and utilize 7/16-inch ARP2000 cap bolts. Used in countless truck pulling and drag racing applications, these rods have been proven to handle more than 2,000 hp without issue.
Ross Racing piston
A forged aluminum, 16:1 compression Ross Racing piston resides in each cylinder. The 4.075-inch bore (vs. 4.055 stock) pistons feature Ross’s black skirt coating, much like hard-anodizing, with a Teflon seal for longer skirt life. To safeguard against piston-to-valve contact at high rpm, 0.095-inch deep valve reliefs are present.
Camshaft from Diesel Technology Source
Valve actuation is controlled via a Dominator series, standard firing order camshaft from Diesel Technology Source. Wagler 4130 Chromoly, 3/8 x 0.135-inch wall pushrods link the cam to the billet rocker shafts (also sourced from Wagler).
Wagler competiton Duramax 6.6L oil pump
With big horsepower comes the need for added oil pressure, and one of Wagler’s pinned oil pumps got the call for this build. The pump’s 0.030-inch shims provide for 25 psi of oil pressure at idle and 90 psi peak. For added peace of mind, the oil pump is pinned to ensure the gear never spins on the shaft.
stainless steel O-rings
For optimum combustion sealing, the block was machined to accept stainless steel O-rings. Wave-Stopper head gaskets from Mahle, feature a patented design that entails concentric waves around the combustion chamber area to allow each gasket to adapt to varying loads and pressures, and accommodate the 0.064-inch thick O-rings.
Dominator series race heads
A set of Dominator series race heads from Diesel Technology Source were supplied for the build and anchored to the block by way of ARP Custom Age 625+ head studs. The stock size intake and exhaust valves were retained (33mm and 31mm, respectively), but the heads underwent extensive CNC porting. As a result, the intake valves flow 225 cfm per cylinder (stock heads max out at roughly 180 cfm).
Dirty Hooker Diesel performance heads
Dual valve springs with Titanium retainers provide the proper spring rate and seat pressure for the kind of elevated rpm and boost levels the engine will see. Also notice the Dirty Hooker Diesel billet-aluminum coolant block-off plate behind the passenger side head, which was installed to rule out the possibility of the common coolant leak occurring at the rear engine cover.
Billet upper valve covers
Topping off the heads, Dermody installed a set of these trick upper valve covers from Wagler. They’re machined from billet 6061 aluminum, feature a leak-free O-ring seal, and come with all 28 required mounting bolts.
 Duramax billet water pump impeller (vs. plastic on late-model Duramax’s)
With the water pump being a common failure point in Duramax mills that see excessive engine speed—and because this engine will often find itself above 4,000 rpm—a welded or pinned factory water pump just wouldn’t suffice. For ultimate peace of mind, a Wagler billet water pump got the nod. It employs a billet impeller (vs. plastic on late-model Duramax’s), a hardened tool steel shaft, ceramic seals, roller bearings, and an anodized hard coat.
PPE Power exhaust turbo pipe T4 pedestal
To avoid overspeeding issues that might surface while running a VGT at high rpm, two fixed geometry turbos are used in the engine’s compound arrangement. Sourced from HSP Diesel, the T4 pedestal for the high-pressure charger utilizes the factory turbo mounting points at the back of the lifter valley. The exhaust gases used to drive the high-pressure turbo route through PPE Power high-flow, cast-iron manifolds, and 2-inch diameter stainless steel up-pipes, both of which are heat-wrapped to aid spool up.
14mm stroker pump from S&S Diesel Motorsport.
Rather than opt for dual CP3’s, Dermody replaced the factory unit with a 14mm stroker pump from S&S Diesel Motorsport. With 71 percent more displacement than a factory CP3, this LBZ-based unit is known to support more than 1,500 hp (at the crank), and also eliminates the 3,000-plus rpm fuel flow restrictions present in stock CP3’s.
S&S Diesel 200 percent fuel injectors
The reason behind the 14mm CP3 becomes clear when you realize it has eight 250-percent over injectors to feed. Also built by S&S Diesel Motorsport, the 250-percent over units are capable of supporting between 1,000 and 1,700 hp (at the crank), depending on how much air you have available. A set of Industrial Injection’s billet-steel injector hold-downs (with ARP mounting bolts) fasten the S&S injectors in place in the heads.
BorgWarner S366 SX-E Turbo
A high-rpm engine presents a unique challenge in turbo selection. First things first, you want turbos that aren’t out of steam at 3,500 rpm. However, you also need them to be as responsive as possible at low rpm. To perform well in both extremes and last while doing it, Dermody turned to the proven S300 and S400 platforms available from BorgWarner. Starting with a box S366 SX-E (the unit shown), the turbo was treated to compressor wheel, turbine wheel, and map groove work, which culminated in a 15-percent gain in flow. The T4 charger retains its 360-degree thrust bearing assembly for optimum shaft support and makes use of a 73mm (exducer turbo) turbine wheel inside a 0.91 A/R exhaust housing.
PPE Power oil pan
With the long block assembled and the CP3, injectors, and turbo pedestal installed, an oil pan from PPE was bolted on, too. The cast-aluminum pan is designed to drain completely but also adds an extra quart to the engine’s oil capacity.
BorgWarner S480 SX-E Turbo charger
Picked to serve as the atmosphere turbo, an S480 SX-E-based charger sits next to the passenger side battery. It too benefits from the compressor and map groove enhancements, as well as flowing approximately 15 percent more air than it did in stock form (135 lbs/min or roughly 1,930 cfm, stock). The big T6 turbo conceals an 88/96mm turbine wheel inside a 1.32 A/R exhaust housing.
The Max-Flow Y-bridge, 3-inch hot-side, and 3-inch cold-side intercooler pipes
To keep both the free-flowing S480 SX-E as responsive as possible while also reducing radiant heat under the hood, a DEI turbo blanket is employed, along with an exhaust wrap around the HSP Diesel hot pipe. The Max-Flow Y-bridge, 3-inch hot-side, and 3-inch cold-side intercooler pipes were also sourced from HSP. The S400 routes exhaust out a 4-inch downpipe.
XD motor mounts from the Dmax Store
Back in the truck, the freshly-built LMM rests on XD motor mounts from the Dmax Store. An LML-derived upper radiator hose, Mishimoto intercooler, DTS-built Allison six-speed, BD Diesel Double-Stack transmission cooler, 260-gph FASS Fuel System, and RCD Performance sump would also be installed before all was said and done.
Custom Tuning by EFI Live
For Dermody, the last order of business before handing the keys over to the truck’s owner entailed 100 break-in miles and a trip to the chassis dyno. Aboard the rollers, a little EFI Live magic from the tuning gurus at Custom Tuning Team will be used to get the truck as far into four-digit horsepower territory as possible.
As an extreme example of what a de-stroked Duramax is capable of, look no further than Tony Rizzi’s Outcast. The Nitrous Express -huffing short-stroke in his ’37 Chevy pickup spins an insane 7,800 rpm, has carried him through the eighth mile in as little as 4.5 seconds, and has been as fast as 171 mph. Factoring in the truck’s trap speed with its race weight, more than 2,000 hp is making it to the rear wheels.



Callies Performance Products

Dermody Diesel

Diesel Technology Source

Dmax Store


HSP Diesel

Industrial Injection


PPE Power

RCD Performance

Ross Racing Pistons

S&S Diesel Motorsport

Sun Coast Converters

Wagler Competition Products


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