Nitrous-Specific Cam Test - Bottle Built

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

Richard Holdener May 4, 2007 0 Comment(s)
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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.

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Nitrous motors really respond well to dedicated cam timing.

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?

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Zex supplied a complete plate nitrous system that allowed us to adjust the nitrous delivery from 100 hp to as high as 200 hp.

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.

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Our 350 was equipped with AFR 190 heads, a Performer RPM Air Gap intake, and a Barry Grant 750 Mighty Demon carburetor. The long-block was first equipped with a factory Chevrolet (200-hp) hydraulic flat tappet cam.

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.




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