The Zex kit differed from...
The Zex kit differed from most nitrous kits by way of this custom plate. Rather than the typical spray bars, the Zex plate featured individual machined orifices to inject the fuel and nitrous.
With our cam and nitrous at the ready, we installed the test engine on the dyno and dialed-in the combination with the stock cam. After tuning the 350 with jetting and timing, we were rewarded with peak power numbers of 343 hp and 397 lb-ft of torque. Even saddled by the stock cam, the 350 managed to produce over 350 lb-ft of torque from 2500 rpm to 5100 rpm.
Adding the nitrous to the stock cam resulted in a jump in peak power from 343 hp to 429 hp, a gain of 86. The nitrous improved the power output with the stock cam by as much as 110 hp (at 4100 rpm), but the gains fell off to 84 hp at 5300 rpm. Part of the drop in power (as engine speed increased) can be attributed to the 4-degree drop in timing that was recommended by Zex for the 100-hp nitrous shot. Retarding the timing by 4 degrees was done to minimize the chance of harmful detonation. The drop in timing would have more of an effect on the power at higher engine speeds. The torque gains were impressive, as the Zex system increased the torque production by 140 lb-ft, from 397 lb-ft to 537 lb-ft. Believe me, an instant gain of 140 lb-ft is anything but subtle.
Solenoids controlled the activation...
Solenoids controlled the activation of the nitrous and additional fuel.
After running the nitrous with the stock cam, we set to work swapping in the new NX256H grind from Comp. Swapping the cam required removal of the intake and carb along with the rockers, pushrods, and lifters. Naturally, we took the liberty of replacing the used hydraulic lifters with the new set provided with the cam. The new lifters were pre-lubed in fresh Lucas 30W oil before assembly. The cam received a liberal dose of assembly lube, as did the entire valvetrain before reassembly.
One trick new product we employed during the cam swap was Comp's Valve Train Assembly Spray. This made lubricating the valvetrain a snap. After adjusting the valves (1/2 turn past 0 lash), we were ready for the 20-minute break-in procedure. After we were sure the cam and lifters were happy in their new home, we were safe to make full-throttle runs.
The new cam profile required only minor jetting (1 jet size), but the power difference was certainly impressive. Equipped with the NX256H cam, the 350 now produced 399 hp and 407 lb-ft of torque. You will remember that the motor produced just 343 hp (and 397 lb-ft) with the stock cam. Despite being designed specifically for nitrous use, the cam improved the power output of the normally aspirated motor by more than 50 hp. In fact, the largest gain was nearly 65 hp out at 5600 rpm.
Before performing the cam...
Before performing the cam swap, we ran the 350 with the stock cam both normally aspirated and with the Zex nitrous kit (set to deliver 100 hp). Equipped with the stock cam, it produced 343 hp and 397 lb-ft of torque.
While wilder cam timing will usually yield big top-end gains, usually gains are accompanied by a trade-off in power down low. This particular cam swap was all but the exception to that rule, as the impressive top-end power cost little, if any down low. There was a slight drop at 2500 rpm, but the bigger cam kept pace with the stock cam from 2700 rpm all the way to 4300 rpm, where the NX cam just took off. Where the torque curve fell off rapidly with the stock cam, it continued strong for another 1000 rpm before starting its decline. The result of this shift in the torque curve was a sizable jump in power production.
We were quite pleased with the gains offered by the nitrous cam on the normally aspirated combination, as we could enjoy the extra power on a daily basis without having to suffer any loss in low-speed power. Now we wanted to see if the gains would continue once we engaged the nitrous. Using the same 100-hp jetting and 4-degree timing drop, we activated the nitrous with the NX256H cam. The results were impressive, as the peak power numbers jumped from 399 hp and 407 lb-ft of torque to an even 500 hp, and an amazing 567 lb-ft of torque.
The nitrous kit improved the peak power by 101 hp and peak torque by 160 lb-ft. The nitrous offered gains ranging from 133 hp at 4200 rpm to 100 hp at 5300 rpm. The power gains offered by the same 100-hp shot of nitrous were greater with the nitrous cam profile than the stock cam, indicating that cam timing does indeed play a part in an effective nitrous motor. The nitrous cam also works well without the nitrous and makes this type of cam swap a no-brainer.