ZEX to the Max

By Richard Holdener/Photos By Author

Generally speaking, when we run nitrous testing, we take a good motor and add 100-150 HP using a plate or single fogger nozzle. Nitrous oxide is an impressive power adder, offering an unmatched combination of power and pricing. Nothing you buy can increases the power output of your motor (any motor) by 100, 150, or even 200 hp for less money. Toss ease of installation and potential concealment into the mix, and it easy to see why nitrous oxide continues to be so popular.

Adding nitrous to any motor is both safe and effective, if applied properly. Add the right amount of fuel and retard the timing per the instructions, and your nitrous motor should live a long, happy life. But, like any modification, if done improperly, things can go bad in a serious hurry. This situation often occurs when nitrous owners get greedy. If a 100-HP shot is good, then a 150-HP shot is better. Pretty soon, that even becomes too tame, forcing you to step up to a 200-HP shot…and so it goes!

The problem with getting greedy with nitrous is that the more power you add to your combination, especially a stock or street motor, the smaller the margin for error. A minor mistake (too lean or too much timing) with a 100-HP shot might not cause a problem. The same scenario at 200 HP can spell disaster. Of course, people are quick to blame the nitrous for their mistakes, but the reality is that properly tuned, your only real issue will be keeping the bottle full. It is with this more-is-better philosophy that we decided on a test using the ZEX Perimeter Plate nitrous system.

Using a guinea pig of a motor, our goal was to max out the power capabilities of the ZEX plate system. Having run endless tests at the lower end of the adjustable power scale (ZEX advertises the kit range from 100-300 HP), we decided it was high time to head for the top. ZEX obviously had no problem supplying the nitrous system, as long as we made sure to properly tune the combination and allow the system to shine. With a system in hand, all we needed was a suitable test mule.

Lucky for us, nitrous motors were available by the hundreds at our local LKQ Pic Your Part. That’s right folks, rather than build up some dedicated nitrous motor with forged internals, we decided to go the low-buck route. As luck would have it, we managed to secure a complete 5.3L LM7 from a 2003 pick up.

The motor was immediately taken to Westech Performance for modifications that included replacement of the factory EFI with carburetion. We also replaced the wimpy stock cam with a more powerful grind from COMP Cams and finally installed an MSD ignition controller. The healthy COMP cam offered a .614./.624 lift split, a 227/243-degree duration split, and 113-degree lsa. The cam was teamed with a set of 26918 beehive valve springs, but the 706 5.3L heads were otherwise untouched. In fact, the heads were not even removed and still retained the factory head gaskets and bolts. Would they survive the nitrous abuse? Time would tell. The 5.3L was finished off with a Holley single-plane intake and 650 HP carburetor, using longer carb studs (from Speedmaster) to allow for installation of the ZEX nitrous plate.

The first step was to run the motor in normally aspirated trim to establish a baseline. This allowed us to determine the amount of power added by the nitrous. Run in anger with the 650 carb and 1 7/8-inch headers, the 5.3L produced 454 HP at 6,700 RPM and 396 lb-ft of torque at 5,200 RPM.

With our baseline out of the way, we plumbed the ZEX Perimeter Plate for action. We installed jetting said to provide an extra 100 HP. In anticipation of the nitrous use, we replaced the pump gas with 118-octane race fuel. This allowed us to get aggressive on the tune-up. Run with 5.75 psi of fuel pressure feeding the 40 fuel jet (43 was recommended) and 2 degrees of timing retard, the nitrous injected 5.3L produced 591 HP and 521 lb-ft of torque. The 100-HP nitrous jetting increased the power output by as much as 137 HP.

Satisfied with the first step, we proceeded to go all in and increase the jetting to further enhance power production. After stepping up considerably, we began to realize that no matter how much nitrous jetting we tried, the system simply would not flow anymore, but not before exceeding the rating of 300 HP. Equipped with a 105 nitrous jet, the ZEX-injected 5.3L put down 756 HP and 638 lb-ft of torque. Pretty impressive for a junkyard motor!

Graph 1: Carbureted 5.3L-NA vs ZEX Nitrous (100-hp Jets)

Run on the dyno in normally aspirated trim, the mildly modified, carbureted 5.3L produced 454 HP at 6,700 RPM and 396 lb-ft of torque at 5,200 RPM. After adding the ZEX Perimeter Plate with a 46 nitrous jet, the power output jumped to 591 HP and 521 lb-ft of torque. As is evident by the power curves, the ZEX kit offered impressive gains. Using race fuel, we retarded the timing by 2 degrees and kept the air/fuel mixture in the mid 12s to maximize power production with the nitrous.

Graph 2: Carbureted 5.3L-NA vs ZEX Nitrous (300-hp Jets)

After a successful test with the 100-HP jetting, we stepped up our game significantly. It seems we managed to reach the flow limit of either the solenoids or the plate itself, as increasing the size of the nitrous jet eventually had no effect on power. The best run we managed with the plate produced peak numbers of 756 HP and 638 lb-ft of torque. We had successfully improved the power output of our 5.3L by over 300 HP. Pretty impressive stuff considering the mileage and stock head bolts.