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Nitrous-Specific Cam Test - Bottle Built

Do nitrous-specific street cams really work? We hit the dyno to find out

By Richard Holdener, Photography by Richard Holdener

By now we all know that nitrous oxide is a performance enthusiast's (and street racer's) best friend. There is nothing that wakes up a motor like a quick shot of nitrous oxide. Need to increase the power output of your motor by 50, 75, 100, or even 300 hp? There is nothing that combines the power potential, ease of installation, and bang for the buck like a well-designed nitrous oxide system. In less than an afternoon, you can transform your mild-mannered machine into a serious street/strip terror.

Even running a conservative amount of nitrous (like we did on our mild 350) can increase the power output by an easy 100 hp. That translates into a solid second off your quarter-mile time and a gain of nearly 10 mph, thereby transforming your 13.8-second stocker into an honest 12-second street slayer, all at the push of a button. While the power gains offered by nitrous are certainly impressive, there's even more power waiting to be unleashed with the proper cam timing. Just like forced induction applications, nitrous engines respond favorably to specific cam timing events. To illustrate the benefits offered by a dedicated nitrous cam, we devised a suitable comparison test.

Naturally, this would require a cam swap while on the dyno. To properly illustrate the power gains, we would have to run our test small-block with nitrous using the stock cam, and then again once we installed the nitrous cam. The flow (or hp shot) of nitrous would have to remain the same, as would things like oil, water, and air temperature, not to mention the air/fuel ratio, and timing. It is imperative that these variables be fixed so they don't affect the outcome of the test.

While performing the nitrous cam comparo, we could also demonstrate the power offered by the cam swap alone (without running nitrous), since the vast majority of the engine operation (especially on a daily driver) will be without nitrous. The question on the table was would the cam swap be beneficial to the normally aspirated combination, or would we have to run the juice to take full advantage of the additional power gains?

Since the vast majority of enthusiasts don't prowl the streets with dedicated nitrous motors, we decided it would be prudent to test the effectiveness of the nitrous cam on a real street powerplant. By "real street" we mean something that could be considered for use as a daily driver. And we don't mean a nasty combination that can be tolerated, but rather one that will yield a delicate balance of performance, mileage, and driveability (even in bumper-to-bumper traffic).

Our test mule certainly qualified as a daily driver, offering nearly 20 inches of vacuum thanks to the use of a production (200 hp) 350 hydraulic flat-tappet cam. A dead smooth idle is one of the qualities offered by a stock cam profile, though (as we would find out), the cam limited power production in the upper rpm range. In addition to the factory cam profile, the 350 small-block featured AFR 190 heads, an Edelbrock Performer RPM Air Gap intake, and a Barry Grant Speed Demon carb. The static compression was less than 10.0:1, something that could easily run on pump gas thanks to the use of the aluminum heads. Additional mods included an MSD distributor, Hooker headers, and 1.6:1 ratio rockers.

The first order of business was to select a suitable cam profile and a matching nitrous system. For our cam needs, we turned to the Comp Cams catalog and went straight to the section labeled nitrous cams. Given the daily driver status of our test motor, we chose the smallest hydraulic flat-tappet nitrous cam listed for a small-block Chevy. The NX256H cam offered a 212/222 duration split at .050 (this compares to just under 200 degrees for the factory cam), a .434/.464 lift split (calculated with a 1.5 rocker), and a 113-degree lobe separation angle. With our 1.6 ratio rockers, the NX256H cam actually provided .463 lift on the intake and .495 on the exhaust. Naturally the stock cam benefited from the additional lift (and reduced friction) offered by the 1.6 ratio rockers.

For the nitrous, Zex supplied one of its adjustable plate nitrous systems that allowed us to dial-in the power gains by changing the jets. Once again, we continued with the conservative approach and installed jetting to increase the power output by 100 hp, though jetting was available to more than double that if our 350 could withstand the additional cylinder pressure.

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.

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.

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.

While testing the mild small-block 350, we compared the stock (200 hp) 350 hydraulic flat-tappet cam against the Nitrous HP NX256H with and without the nitrous. Replacing the mild factory cam with the NX256H resulted in a significant jump in power. The larger cam profile lost little, if any power down low, but showed significant power gains past 4300 rpm. The curve indicated that the engine would now pull strongly to 6000 rpm, where the power was falling off hard with the stock cam.

Before we performed the cam swap to the NX256H, we ran the Zex plate nitrous kit on the small-block equipped with the stock cam. Running the nitrous system on the 350 with both cams helped illustrate the power gains offered by the cam swap both normally aspirated, and with the nitrous. Running a 100-shot (46 nitrous jet and 43 fuel) through the Zex plate system resulted in a jump in peak power to 429 hp and 537 lb-ft of torque. The torque gains exceeded 100 lb-ft mostly because the nitrous was engaged low in the rpm range (3500 rpm). After replacing the stock cam with the NX256H, we once again installed the Zex plate nitrous kit, and ran the identical jetting and timing with the nitrous cam. The results were impressive. The nitrous system increased the power output of the 350 test motor from 399 hp to 500 hp, a gain of 101 hp. The torque gain was even more impressive, as the nitrous-equipped small-block thumped out 567 lb-ft of torque, a gain of 160 lb-ft.

SOURCES
Barry Grant
Dahlonega
GA
706-864-8544
www.barrygrant.com
Zex
3418 Democrat Rd.
Memphis
TN  38118
COMP Cams AFR
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By Richard Holdener
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