COUNTRY Brawler: 1,075 hp in an Unassuming GM

2015 Chevy Silverado LTZ
There are some people who throw in the towel if problems arise, and then there are others who come back stronger. Ricky Rosonke, of New Hampton, Iowa, is the latter. After just 7,000 miles, the Duramax engine in his ’15 Chevrolet decided to spit the crank out, destroying the engine. Rather than just throw a new stocker in, Rosonke decided to go big.

Forward Progress

When deciding what to do with his now-broken truck, Rosonke felt like he should start from scratch and enlisted the help of Corey Streif from No Limit Diesel. The engine was rebuilt from the bottom up, including a new LML crankshaft, and would be secured with ARP studs and a girdle this time. The rods are also aftermarket versions that are much stronger (from Carrillo), and the pistons are Mahle forged 0.020 over stock. With the engine apart, it didn’t make sense to leave the camshaft or valvetrain alone, so again it was time to hit the parts catalog. A SoCal Diesel Alternate Fire Order camshaft was selected, and the heads were ported and fitted with upgraded valve springs and pushrods. Just like the crank, the heads were also secured with ARP studs to prevent blown head gaskets under high boost.

Rosonke chose the largest S300-based turbo you can currently buy (a 69mm) as the smaller high-pressure turbocharger. This BorgWarner turbo combines an S400-sized compressor wheel along with the smaller S300 frame.
Rosonke relies on compound turbos and twin CP3 pumps to make an estimated 1,075 rear-wheel horsepower along with 1,850 lb-ft of torque

Fuel and Air

With a bottom end built to handle more than 1,000 horsepower, Rosonke now just needed the performance parts to get there. Since he wanted the power to be available at all times, he stayed away from water-methanol injection and nitrous and instead decided to go the compound turbo route. Fortunately for Rosonke, Wehrli Fabrication was able to come to the rescue. For the big turbocharger, an 84mm S400 was selected to make sure that the truck could hit the peak number, while a smaller-frame 69mm S300 got the nod for the smaller turbo thanks to its quick spooling. Both turbos combine along with tuning from Duramax Tuner to hit an impressive 65 psi of boost. Wehrli also got the call when it came to fueling, as the factory CP4 pump was replaced with a CP3. Then a second one was mounted up top with one of Wehrli’s twin CP3 kits. Exergy Engineering got the call for injectors, which are 100% over versions.

With an engine that produces more than three times the original output, Rosonke couldn’t rely on the factory Allison 1000 six-speed to handle the power. Here again he sought help from No Limit Diesel. After building an engine from the ground up, Rosonke wasn’t going to skimp on the transmission, and had Scheif throw virtually every part you can at an Allison. The C2 and P2 planetary gears were upgraded, as were the clutches and the input, output and intermediate shafts. Scheif also put a deep pan on from Pacific Performance Engineering to help handle the extra power.

Just like the exterior of the truck, the interior is fairly stock except for an Edge monitor that keeps an eye on boost, EGT and other engine parameters.
Rosonke went to the bottom of the turbo catalog for the large turbo, an 84mm S400. The big BorgWarner combines with the smaller 69mm S300 to produce an impressive 65 psi of boost.
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Sleeper Status

With an extreme engine and highly modified transmission, it may come as a surprise as to how stock the rest of Rosonke’s truck is. “I sort of like to fly under the radar—no huge wheels, no big exhaust, nothing like that,” he states. The front suspension is also stock, as Rosonke indicates he tries to stay away from hard four-wheel-drive launches. Does he regret building such a wild truck right off the bat? “Once you get it rolling, it’s definitely surprised some sports cars and it’s a heck of a fun truck,” he says.