There are two kinds of performance enthusiasts: those who resist change and those who embrace it. Which one are you? When Chevrolet first introduced electronic fuel injection to the original small-block, the carburetor guys threw their hands up in disgust, thinking it was the death of performance. Not only was this untrue, but it can be argued that fuel injection ushered in the modern muscle-car era. The same thing happened when GM introduced the LS engine family to replace the legendary small-block, and now the LS market is the biggest thing going in the performance industry. Now, the new LT engine platform, introduced in 2014, represents a further step up the small-block performance ladder. Thanks to refinements like variable-valve timing (VVT) and direct injection, the LT engine family not only offers improvements in power production but combines this with fuel-mileage improvements during this time of ever-tightening restrictions on emissions output.
Unlike the LS, the recent LT engine family is offered in only two displacements: 6.2L and 5.3L. The performance-oriented Corvettes and Camaros receive the larger, more powerful 6.2L LT1, LT4, and even LT5 versions, but the bread-and-butter trucks are available with both displacements. Not surprisingly, the 5.3L is the most common, so we decided to get our hands on one for some dyno testing.
With a designation of L83 by GM, this 5.3L was factory-rated at 355 hp and 383 lb-ft of torque. These peaks jumped to 380 hp and 416 lb-ft when run on E85. The peak numbers are impressive compared with the nearly 300 hp offered by the previous LM7 (LS-based) 5.3L, but it is the average torque production offered by the L83 that is most impressive. Thanks to the combination of high compression (available courtesy of direct injection) and VVT (advancing and retarding the cam), the L83 offers a solid 50 extra lb-ft of torque at lower engine speeds, where it is most effective in truck applications.
To find out if the L83 responded to the usual array of performance modifications, we started with a kit from Nitrous Express (NX). Before we could run that test, we needed to get the direct-injected L83 up on the dyno and running in naturally aspirated trim. The combination of direct injection, VVT, and drive-by-wire throttle-body meant we could not employ our usual aftermarket ECU for tuning. Luckily, the folks at Gandrud Chevrolet came to the rescue with their engine-controller kit for an LT1. Though the ECU is designed for the larger-displacement LT1, Westech’s Eric Rhee not only got the ECU working on the smaller 5.3L but even managed to delete the factory MAF and air-intake assembly. This allowed us to visually confirm full-throttle activation of the drive-by-wire throttle-body, as well as view the nitrous injection into the 5.3L. A few harness extensions here, a relocated MAP sensor there, and a 60-psi fuel source, and we were in business. Equipped with long-tube headers, the factory accessory drive, and an open throttle-body with a radiused air entry, the 5.3L L83 produced 406 hp at 5,400 rpm and 434 lb-ft of torque at 4,200 rpm. Torque production exceeded 400 lb-ft, even below 3,000 rpm!
In retrospect, we should have run the dedicated system from NX designed for the 2014-and-later 5.3L trucks, but all we had on hand in time for testing was a simple wet fogger nozzle—the kind used on a fifth-gen Camaro kit. To get it ready to run, we drilled and tapped the air entry to accept the threaded nozzle, then installed the supplied nitrous jetting to produce the desired 100 hp (52N/23F). For the fuel supply, we tapped into the 60-psi Aeromotive fuel-pressure regulator, while we plumbed the nitrous solenoid directly from the 15-pound NX bottle. When we hit the button, power output jumped to 549 hp and 613 lb-ft of torque. The activation spike subsided to produce a solid gain of 100 hp over the naturally aspirated combination. Note: Be sure to replace the factory projected-tip spark plugs with a colder, non-projected-tip plug if you plan to Xpress yourself on a daily basis!
5.3L L83-Stock vs. NX Nitrous (100 HP)
The fancy, new 2015 LT-based 5.3L L83 test engine features direct injection and variable-valve timing. Having run endless testing on the previous LS engine family, we couldn’t help but wonder if the new engines responded just as well to a shot of nitrous. Spoiler alert: The answer was an emphatic yes. Run with headers, a radiused air entry, and tuning by Westech’s Eric Rhee, the used L83 5.3L truck engine produced 406 hp and 434 lb-ft of torque. After introduction of the Nitrous Express (NX) wet fogger kit, with 100hp jetting, the power output jumped as high as 549 hp and 613 lb-ft of torque. Once the activation spike subsided, the NX nitrous kit offered consistent 100hp gains through the remainder of the curve.
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