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Cam-Only LS1 Nitrous Engine - Zex Appeal

Our Man Pushes A Cam-Only LS1 Nitrous Engine Past The 550-Horse Mark

Richard Holdener Dec 14, 2006
Vemp_0604_02_z Cam_only_ls1_nitrous_engine Tuned_ls1_engine 2/20

A pretty strong case can be made for Chevy's modern machinery. While we all look back fondly on the musclecars of yesteryear, the reality is that nostalgia has altered our perception somewhat. As great as some of these classics were, time and technology have marched on-to the extent that a modern LS-engined Corvette not only offers every bit as much performance (or more), but does so while delivering a combination of driveability, fuel economy, and reduced emissions only dreamed of by its carbureted forebears.

But while these modern motors are plenty potent, there are always ways to improve their power output. One route-nitrous oxide-was pioneered by the German Luftwaffe, which used the power-enhancing compound to improve the speed and flight ceiling of its WWII fighter aircraft. For those unfamiliar with nitrous oxide-or simply "nitrous," as it's commonly known-the compound contains both nitrogen and oxygen, not unlike the air you and your motor already breathe. It is actually the oxygen contained in this compound that's responsible for the additional power.

Before we proceed, let's dispel one persistent nitrous myth. Contrary to what you might have seen on TV, touching a lit match to a stream of nitrous will result in very little drama. In fact, the match will simply go out. But while the compound itself is not flammable, the oxygen contained within it is. Fortunately for enthusiasts, it requires a great deal of heat (572 degrees F) to liberate these oxygen molecules. In an internal-combustion engine, this heat is supplied by the gasoline-fueled combustion process, which, in turn, is greatly enhanced by the freed oxygen molecules.

Vemp_0604_01_z Cam_only_ls1_nitrous_engine Wet_nitrous_system 3/20

Our nitrous came from this Zex wet system. The Zex kit supplied both fuel and nitrous through a common fogger nozzle.

As if the release of power-producing oxygen molecules weren't enough, additional power gains are realized by an accompanying reduction in inlet-charge temperature. For automotive use, nitrous is stored, under pressure, as a liquid. When injected, the nitrous is converted into a gas, a process called "boiling." The liquid-to-gas conversion absorbs a great deal of heat from the surrounding area-in this case, the inlet air. While we normally associate boiling with extreme heat, the boiling point of nitrous oxide is actually a chilly -129 degrees. Cooler inlet air is rich in oxygen molecules, which, as noted earlier, enhance combustion and, in turn, power. Not surprisingly, the combination of extra oxygen molecules and a cooler inlet charge can produce some pretty impressive power gains.

One of the great things about nitrous is that it doesn't require expensive supporting upgrades to the engine. By cooling the inlet charge, nitrous not only improves power output, but it also helps suppress harmful detonation. The separation of the nitrogen and oxygen molecules during combustion also helps minimize detonation. This built-in "detonation control" allows impressive power gains without fear of component damage-even on a stock motor with cast pistons.

Vemp_0604_06_z Cam_only_ls1_nitrous_engine Hydraulic_roller 4/20

Comp Cams supplied this Xtreme RPM XR265HR hydraulic roller. Don't let the name fool you: This relatively mild cam offered impressive midrange and low-end torque gains to go along with the additional high-rpm power. Its 212/218-degree duration split improved output throughout the rev range and proved a perfect match for our nitrous kit.

Keep in mind that the power gains and life expectancy of a motor are directly related to its tuning, as a proper air/fuel mixture and ignition timing are critical in a nitrous application. Applied and tuned properly, a modern nitrous system can provide safe, effective, and reliable power gains.

While nitrous will definitely wake up a stock LS1, there are ways to further improve its power-enhancing properties. This is where cam timing can play a part, as increasing exhaust lift and duration relative to intake will help rid the combustion chamber of all those extra oxygen molecules. To illustrate the gains offered by both cam timing and nitrous oxide, we set up an engine-dyno test using a mild LS1 equipped with a stock long-block, a FAST LSX intake and throttle body, and a set of Hooker headers.

The idea was to subject the LS1 test mule to nitrous oxide using the factory cam, then again with a slightly wilder-but still streetable-cam profile. Given the stock nature of the long-block and the fact that all of our tests would be conducted using 91-octane gas, we kept the nitrous shot at a conservative 100 hp. Such a combination could easily be duplicated on a typical street Vette.

Vemp_0604_07_z Cam_only_ls1_nitrous_engine Controller 5/20

This trick aluminum controller was responsible for engaging the nitrous. The sophisticated circuitry built into the controller monitored the throttle-position sensor to ensure that the motor was at wide-open throttle before the nitrous could be activated. Part-throttle nitrous activation can produce catastrophic results.

The motor was equipped for dyno use with a FAST engine-management system and 36-pound injectors. The FAST system allowed us to dial in the timing and fuel curves to optimize the power produced by each camshaft. We tuned the combinations to produce a 13.1:1 air/fuel ratio and 30 degrees of total timing (any more or less reduced power). Thus configured, the LS1 produced 419 hp and 414 lb-ft of torque without nitrous. Before engaging our Zex wet fogger system, we retarded the timing by 4 degrees to reduce the chance of detonation.

This change dropped the power output to 402 hp. Activating the Zex system increased the peak power output to 528 hp, while peak torque shot to 559 lb-ft (see the accompanying graph for full details). Overall, the nitrous improved power output by 109 hp and torque by 137 lb-ft. With well over 500 hp, our LS1 was squarely into LS7 territory-and we had yet to change the cam.

Vemp_0604_08_z Cam_only_ls1_nitrous_engine Fogger_nozzle 6/20

Both fuel (from the fuel rail) and nitrous (from the bottle) were supplied by the controller to this single fogger nozzle. The flow orifice was designed to atomize the fuel and nitrous for maximum power production. We installed the fogger nozzle into a radiused air horn positioned in front of the throttle body.

Since Comp Cams didn't offer a dedicated LS1 nitrous cam at the time of our test, we selected the profile we felt best suited our testing parameters. Although the XR265HR was the smallest cam in Comp's Xtreme RPM category, we expected it to deliver some serious power in our test engine. The profile offered a .522/.529 lift split, a 212/218 duration split (at .050), and a suitably wide 114-degree lobe-separation angle. No valvespring change was required with this cam, but Comp offers an "RPM" package-with heavy-duty valvesprings, pushrods, and retainers-in the event you'd like to upgrade.

Performing the cam swap in the LS1 was a breeze compared with a conventional small-block. All we had to do was remove the rockers and front cover, then rotate the cam to push the factory lifters up and out of the way. The entire swap took less than an hour to perform. The new cam increased the power output of the LS1 from 419 hp and 414 lb-ft to 447 hp and 433 lb-ft. Better yet, power increased at all points on the dyno graph-a sign our cam choice was spot-on.

Activating the nitrous upped the power numbers even further, to peaks of 559 hp and 587 lb-ft of torque. The Zex nitrous (with the same 100hp shot and 4 degrees of timing retard) improved the power output of the upgraded-cam engine by 112 hp and 154 lb-ft. The right cam obviously made a difference.

Vemp_0604_03_z Cam_only_ls1_nitrous_engine Nitrous_dyno_test 7/20

Before performing the cam swap, we ran the Zex wet nitrous system with the stock LS1 cam. Thus equipped, the mild LS1 motor (FAST intake, Hooker headers, and a FAST management system) produced 419 hp and 414 lb-ft of torque. Engaging the Zex nitrous increased the peak numbers to 528 hp and 551 lb-ft of torque. It should be noted that we retarded the ignition timing by 4 degrees (as per the Zex instructions) before activating the nitrous. The drop in timing reduced the (non-nitrous) power output from 414 to 402 hp, so the gain offered by the nitrous was even more significant than demonstrated by this graph. Jetted to deliver 100 hp, the Zex system improved the power output of our LS1 by 109 hp and a whopping 137 lb-ft.

Vemp_0604_04_z Cam_only_ls1_nitrous_engine Dyno_test 8/20

As is evident from the graph, installing the Comp XR265HR cam (.522/.529 lift, 212/218 duration, 114 LSA) offered a significant increase in power over the factory cam. While we normally expect impressive power gains with a wilder-than-stock cam profile, a trade-off in low-end torque is often associated with such a swap. The unique design of the Xtreme RPM LS1 cam not only provided a sizable power gain up top, but it also offered over 50 lb-ft of torque down at 3,500 rpm. In total, this cam profile increased the peak numbers from 419 hp and 414 lb-ft of torque to 447 hp and 433 lb-ft.

Vemp_0604_05_z Cam_only_ls1_nitrous_engine Comp_grind_dyno 9/20

Since the Comp catalog didn't offer nitrous-specific cams for the LS1, we chose a popular performance grind that offered exceptional power gains throughout the rev range. The thinking behind a nitrous cam is that all the extra power-producing oxygen molecules injected into the intake tract must eventually find their way out through the exhaust. This is usually accomplished by increasing exhaust duration. Accordingly, we selected Comp's XR265HR grind, which features a 6-degree duration split (212 intake/218 exhaust). Equipped with this cam, our LS1 produced 447 hp and 433 lb-ft of torque. Engaging the nitrous increased the peak numbers to an amazing 559 hp and 587 lb-ft. As before, we reduced the timing by 4 degrees (from 30 to 26 degrees) during the nitrous run, which cost the motor about 15 hp. Allied with the Comp cam, the nitrous system improved peak output by 112 hp and 154 lb-ft of torque-both numbers bettering the improvements realized with the stock cam.



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