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Dream Duramax: 2003 GMC Sierra 2500

A Compound-Turbo GMC Built Right— The Second Time Around

Text By Jason Thompson, Photography by Jason Thompson

Andrew Murdoch thought he paid a reputable shop to turn his ’03 GMC Sierra into a high-horsepower monster. What he got instead was a horrible mess. When an incorrectly ported cylinder head cracked and allowed coolant to flow into the combustion chamber, his brand-new (and expensive) built motor was ruined. Diagnosing the Duramax’s failure was a nightmare because almost every sealing surface on the drivetrain leaked. The transfer case was the only exception—but that was because nobody had ever refilled it with ATF.

Taking the devastated engine apart was easier than you’d think, because upon beginning the initial teardown, Andrew found out his Duramax’s valve covers were cracked, and many of the bolts were missing. The engine wasn’t a total loss, but it was close.

Duramax Redo: Round Two
None of us would have blamed Andrew if he had given up on diesel performance at that point. After such a horrific experience, he could have just walked away from his dreams, returned the truck to stock, and cut his losses. But he didn’t. Nope, after a series of emails, phone calls, and private messages, Andrew got in touch with Newly Tolf at Underground Diesel in Las Vegas. The two men discussed what had happened to the truck, the condition of the parts, and the cost of doing the job right. When Tolf got off the phone, he hitched a trailer to the back of his C4500 and drove to Colorado to personally pick up Andrew’s GMC.

When the truck was rolled into the shop, Tolf’s staff immediately set to work on righting all the wrongs that had been done to this ’03 ¾-ton. After a few weeks, the test fitting of a few prototype parts, and a compound-turbo kit install, Andrew’s LB7 Duramax rolled back out of the shop—but this time under its own power. Right before Andrew flew into town to pick up his second-chance Sierra, Tolf took us for a cruise in the truck on the Vegas strip so we could witness firsthand what a twice-built Duramax diesel can do.

By Jason Thompson
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