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Modern Muscle: Zex-Injected DI L83

Nothing wakes up a new direct-injected, LT-based motor like a little Zex!

Nothing wakes up a new direct-injected, LT-based motor like a little Zex!

 Like anything new, the arrival of the junkyard L83 5.3L at Westech was met with a certain amount of skepticism. Having run endless testing on the previous generation LS engine family with tremendous success, we really didn’t know what to think about the new direct-injected LT motor. The LS was such a huge jump in performance over the previous Gen-2 small block, we couldn’t help wondering just how much power was actually left on the table.

 

Thanks to their responsiveness to performance upgrades, the popularity of the LS was in full swing, but how long would it last? Production of Chevy’s little wonder motor had ceased long ago (with the exception of a single 6.0L truck model), and the question now was, would the replacement LT engine family be able to carry the performance torch? The only way to find out if the LT engine family was a worthy successor, was to get one up on the dyno, and start testing. To that end, we located a 2015, direct-injected, junkyard 5.3L L83 and had it shipped over to Westech. 

Normally, when we run a performance tests on an LS motor, we utilize a Fast XFI engine management system, but for this junkyard, nitrous adventure, we chose to run the DI 5.3L with the factory ECU. Allowing us to do so was a GM Performance engine controller kit from Gandrud Chevrolet. Originally designed for a crate 6.2L LT1 application, we made it work on the smaller 5.3L. After a few changes to the harness (plugs are in different spots on the 5.3L compared to the 6.2L), the 5.3L roared to life.

Using HP Tuners, we were then able to manipulate the tune on the factory computer to dial in the air/fuel, ignition and cam timing on the direct-injected 5.3L. Though we started off the adventure by running the supplied factory air intake and MAF assembly, Westech’s Eric Rhee managed to work his magic so we could run the 5.3L in speed-density mode. This meant we could replace the stock air box with a simple radiused air entry and (best of all) could actually verify that the DBW throttle body was going to WOT when commanded. It also allowed us to see the Zex nitrous being injected into the intake during the test-cool stuff! 

Run on the dyno in stock trim, the direct-injected 5.3L L83 produced 401 hp at 5,500 rpm and 429 lb-ft of torque at 4,300 rpm.

Run on the dyno in stock trim, the direct-injected 5.3L L83 produced 401 hp at 5,500 rpm and 429 lb-ft of torque at 4,300 rpm.

Though we have plans to run a variety of different modifications on the 5.3L L83, including cams, ported heads and even boost, we started off with something both simple and powerful, meaning nitrous oxide. Thanks to television and the movies, nitrous oxide is as popular as ever. As we would see on our DI 5.3L, the reason for the popularity is a combination of cost, simplicity and effectiveness. Nothing adds as much bang for as little bucks as a nitrous kit.

The right cam installed on an LS might come close, but it will never offer the instant rush of torque like a shot of the juice. Besides, if 100 hp isn’t enough, thanks to the adjustable nature, you can always step up to 200 hp, 300 hp, or even more. Such is the beauty of nitrous oxide. Every bit as important as the significant gain in power is the ease at which the power comes. Nitrous oxide is both easy to install and even easier to conceal, should you be wanting to add a little hidden horsepower. What started out as an anesthetic and power augmentation for military aircraft, has become the go-to performance upgrade for automotive enthusiasts everywhere. 

Checking our list, we had one direct-injected, Chevrolet performance engine and one power adder with nothing but potential, so we did what comes natural, we combined the two. The engine side of the equation was obviously was taken care of by the 2015 L83 5.3L, so all we needed now was the nitrous. To supply nitrous to our direct-injected motor, we chose a Zex wet efi system.

Though originally designed for a lowly Mustang, we made the system work on our Chevy. The Zex system featured a controller designed to learn the voltage output of the TPS sensor. This safety feature can be thought of an electronic version of the wide-open-throttle switch. The Zex system will only activate once the controller senses WOT TPS voltage. In addition to the controller, the Zex kit also featured a 10-pound bottle and jetting to allow adjustment of the power supplied by the kit from 75 hp to 175 hp.

 Run on the dyno with the Zex nitrous system, the direct-injected 5.3L produced peak numbers of 542 hp and 558 lb-ft of to4rque, but the horsepower spike settled in at a more realistic 505 hp. Jetted for 100 hp, that’s exactly what we got on our little, direct-injected 5.3L!

Run on the dyno with the Zex nitrous system, the direct-injected 5.3L produced peak numbers of 542 hp and 558 lb-ft of to4rque, but the horsepower spike settled in at a more realistic 505 hp. Jetted for 100 hp, that’s exactly what we got on our little, direct-injected 5.3L!

 

We chose to add 100 hp to our otherwise stock 5.3L L83. Run on the dyno in stock trim, the L83 produced 401 hp at 5,500 rpm and 429 lb-ft of torque at 4,300 rpm. After activation of the Zex nitrous kit, the peak power numbers jumped to 542 hp and 558 lb-ft of torque, but the real peak horsepower number (after the activation spike) was just a hair over 500 hp, or right at an extra 100 hp. Well, now we know the LT engine responded well to nitrous, so I guess its time for a cam swap!  

5.3L L83-Stock vs Zex Nitrous (100 hp) The latest iteration of the LT-based small block from GM featured direct injection. The question we wanted answered was would this modern muscle respond well to a little shot of nitrous? As it turned out, like every previous generation, the answer was yes. Run in stock trim with the factory ECU, the junkyard, 5.3L L83 truck motor produced 401 hp and 429 lb-ft of torque. After hitting it with a 100-hp shot from the Zex wet EFI kit, the power output jumped to 542 hp and 558 lb-ft of torque, but the big spike numbers settled in to a solid 100-hp gain from 5,500 rpm to 6,500 rpm.

5.3L L83-Stock vs Zex Nitrous (100 hp)
The latest iteration of the LT-based small block from GM featured direct injection. The question we wanted answered was would this modern muscle respond well to a little shot of nitrous? As it turned out, like every previous generation, the answer was yes. Run in stock trim with the factory ECU, the junkyard, 5.3L L83 truck motor produced 401 hp and 429 lb-ft of torque. After hitting it with a 100-hp shot from the Zex wet EFI kit, the power output jumped to 542 hp and 558 lb-ft of torque, but the big spike numbers settled in to a solid 100-hp gain from 5,500 rpm to 6,500 rpm.