De-Stroked Duramax at a insane 7,800 High-RPM

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.

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.

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.

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