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Cummins Swap: Duramax-Powered Chevy Silverado

Duramax-Powered Cummins Swap

In the diesel industry, Cummins swaps are nothing new. The B series inline-six has been the engine of choice for sled pullers, drag racers, rat rods, and (of course) Ford trucks for more than a decade. However, the unwritten rules of engagement in performing a Cummins swap dictate that Duramax-powered trucks are off-limits. With common-rail injection and a proven track record for performance and durability, the 6.6L V8 is more than sufficient in yielding the kind of power most enthusiasts are after. Put simply: you just don’t go there.

“THE CHEVY GUYS GET A LITTLE UPSET, BUT THE DODGE GUYS LOVE IT.”

But then there are young guns like Tyler Rabbage. The 22-year-old Miami native wasn’t afraid to break all the rules in pursuit of adding reliability and horsepower to his ’03 Silverado. After the LB7’s second set of injectors began to go south and its 350,000-mile head gaskets appeared blown, Tyler got to thinking. “I had the choice to either fix the issues with the Duramax or—for the same price—I could put a Cummins in the truck and make more power,” he told us.

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The first charger to grab a bite of air in Tyler’s compound arrangement is a T6 flanged S475 from BorgWarner. Its support bracket ties into the passenger side motor mount, which—along with all intercooler tubing—was fabricated by Felix Aleman of Outlaw Diesel in Miami. Both turbocharger compressor housings, the factory intake elbow, and all intercooler tubes were painted a proprietary blue by Tyler’s friend, Sean Espinosa.

And so, the “Chummins,” as Tyler and his group of friends like to refer to it, was born. Perhaps the wildest part of the entire process was how quickly it all unfolded. Tyler spent his 2016 college Spring Break performing the Cummins swap. In just eight days—and with the help of Outlaw Diesel in Miami—the Duramax/Allison combination was ditched in favor of a compound turbo’d, 12-valve Cummins backed by a built 47RH.

LOW-MILE 12-VALVE

Sourced from Craigslist, the 120,000-mile 12-valve 5.9L was gone through by Tyler and Felix Aleman of Outlaw Diesel in Miami. While the bottom end was left alone, Tyler knew some provisions would have to be made for the head gasket to live at the boost he wanted to run. So, the cylinder head was pulled and sent to Haisley Machine for fire-rings and one of its standard thickness fire-ring gasket kits. Before the head was reinstalled, it was treated to a full port and polish at Outlaw Diesel in Miami, along with 90-ppi valve springs to lower the possibility of valve float or creep. ARP head studs clamp the worked over head to the block. The engine itself rides on factory Dodge/Cummins motor mounts welded to the GM’s frame and, believe it or not, the 5.9L fits better in the Chevy engine bay than it does in a Ram’s. “There’s a lot more room between the rear valve cover and the firewall in the Chevy,” Tyler told us. “The hardest part of the whole swap was actually getting the A/C lines made, as we couldn’t do that ourselves.”

“THE UNWRITTEN RULES OF ENGAGEMENT IN PERFORMING A CUMMINS SWAP DICTATE THAT DURAMAXPOWERED TRUCKS ARE OFF LIMITS.”

PUMP WORK

The fact that the engine was plucked from a ’96 model year Ram with an NV4500 meant it had the highly sought after 215hp P-pump. Along with the normal tweaks (custom fuel plate and AFC adjusted completely forward), the pump benefits from full-cut delivery valves and its timing being set at an aggressive 21 degrees of advancement. The injectors are stock for now—although as we went to press Tyler had a set of 5×18 units from Diesel Auto Power on the way.

BIG BOOST

Pegging the 60-psi boost gauge in the cab comes courtesy of an HX35 over S400 compound turbo arrangement. The BorgWarner S475 is internally wastegated, features a T6 flange, and is supported via a bracket bolted to the passenger side motor mount. The tough-as-nails nature of the factory Holset HX35 got the nod for the manifold charger and produces the lion’s share of boost the engine sees. The downpipe and all intercooler tubes were fabricated by Outlaw Diesel in Miami, while the factory Duramax intercooler was reused.

AXING THE ALLISON

To keep the swap simple (and namely void of electronics), Tyler chose to do away with the five-speed Allison. Instead, the torquey 12-valve is backed by a 47RH four-speed automatic, which (ironically enough) was sourced from the same person that sold him the truck years prior. In order for the 47RH to live behind the Cummins, Tyler once again turned to Outlaw Diesel in Miami for a helping hand. The slushbox was torn down and reinforced with a billet input shaft, a triple disc torque converter from SunCoast, and a performance valvebody fitted with TransGo parts.

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Tyler Rabbage’s ’03 Silverado is one of the few Cummins swaps we’ve seen performed on an ’01-’07 GM where the original power plant was a Duramax.

So what’s it like driving a Cummins-powered ¾-ton Silverado? As you can imagine, Tyler gets the full gamut when it comes to reactions. Comments like “you ruined the truck!” or questions such as “how could you put a Cummins in a Chevy?” come his way on a regular basis. But while the truck seems to ruffle plenty of feathers in the bow tie crowd, Dodge guys and Cummins diehards love the swap. No matter what side of the fence people are on, it gets them talking—and that’s exactly what Tyler wanted. He gets the unmatched reliability of the 12-valve Cummins wrapped in a Chevy body, and the satisfaction of his creation turning heads wherever it goes.

07
An adjustable fuel pressure regulator from VMS Racing keeps a steady diet of diesel on tap for the P-pump. While opinions continue to vary as to what the ideal pressure to send the P-pump’s way is, Tyler keeps the regulator locked in at 50 psi.
04
Providing great bottom end response is a Holset HX35, which when combined with the S475 easily pegs the 60-psi boost gauge on the A-pillar. Two 50mm Tial blow-off valves are incorporated between stages in the charge pipe. Boosted air routes through the truck’s original (Duramax-intended) intercooler.
05
Being a ’96 model year Cummins, it came with the highly desirable 215hp version of the Bosch P7100. Courtesy of Outlaw Diesel in Miami, the 12mm P-pump benefits from a set of full-cut delivery valves, a custom fuel plate, its AFC being adjusted all the way forward, and a healthy 21-degrees of timing.
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Fitting for a rare, Cummins-swapped Silverado HD is a set of wheels we seldom see: 16×9-inch Granite Alloys. They’re wrapped in Nitto Trail Grappler M/T tread measuring 285/75R16.
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With a desire to keep things simple, Tyler scrapped the five-speed Allison 1000 in favor of a 47RH. The fourspeed automatic sports a triple disc torque converter from SunCoast, a billet input shaft, and an Outlaw Diesel in Miami-built valvebody with TransGo internals. In order to make the 47RH work (and because the 5.9L moved the transmission back much further within the truck), the rear drive shaft had to be shortened.
06
On the low-pressure supply side of things, Tyler left nothing to chance. The P-pump is well-fed thanks to a Bean’s Diesel Performance sump installed in the factory GM tank and this 200-gph AirDog II system, which is said to be capable of supporting 1,000hp.
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Make no mistake, the three-ball hitch in the receiver sees its fair share of work, as Tyler uses the truck to tow on occasion. He told us the Silverado gets roughly 11 mpg with a trailer attached, but typically sees 20 mpg when empty.
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It only made sense to retain the burly 11.5-inch ring gear AAM 1150 the Chevy came with, which still utilizes the factory 3.73 ring and pinion. As for the exhaust, it’s made up of a 5-inch diameter, aluminized, over axle system from Flo-Pro that was designed for a Duramax but adapted to work with the Cummins’ downpipe. Tyler topped things off with a 10-inch polished tip.
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If Tyler’s “Chummins” can’t garner enough attention by the 12-valve rattling away under the hood or the giant Cummins sticker on the rear window, a Viair air horn should definitely do the trick.

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