No longer considered the cheater’s power adder, nitrous oxide systems have become a popular and cost-effective method for boosting the power output of late-model vehicles. In fact, a carefully matched nitrous oxide system delivers an excellent performance-per-dollar value, as well as the benefit of no affect on drivability when the system is off.
In short, nitrous is there when desired and invisible when not. A nitrous system also is comparatively easy to install, as we found out with the installation of a ZEX (www.zex.com) system, including an LED-lit purge system, as it was adapted to a Chrysler 300C SRT8. The installation was performed at Paul’s High Performance (www.paulshp.com), in Jackson, Mich.
Nitrous oxide is a compound of nitrogen and oxygen – two nitrogen atoms and one oxygen atom per molecule – and is 66 percent nitrogen and 33 percent oxygen by volume. It is a very “cold” compound; it boils at -129 degrees F (-89 degrees C) and is a gas at room temperature; it requires 760 psi to squeeze it into a liquid.
More important than its volumetric properties is nitrous oxide’s oxygen content by weight, which is 36 percent. The atmosphere is 23 percent oxygen by weight. N2O also is about 50 percent denser than the atmosphere, so a cubic foot of nitrous oxide contains more than twice the oxygen of the air inhaled by humans – or automotive engines.
Like other power adders, such as a supercharger, turbocharger or even a set of high-flow cylinder heads, the optimal air/fuel ratio of the engine must be maintained, as well as spark timing. Simply put, a large increase in cylinder pressure, such as that delivered by nitrous oxide, will likely cause severe detonation without a corresponding change (retarding) of timing. Adequate fuel supply also is a must, as a super-oxygenated air/fuel mixture will go too lean without a matching boost in fuel.
Fortunately, the engine construction and sophisticated controls of most modern vehicles – including 5.7L and 6.1L Hemi-equipped vehicles – are very adaptable to low-to-medium doses of nitrous oxide. The biggest caveats are working with vehicle’s engine controller and being cognizant of the engine’s durability limit.
What does that mean on the Hemi engine? Without any computer programming that drastically retards timing, the horsepower “hit” of the nitrous is limited to about 75 horsepower. For a 100-horsepower “shot,” 2 degrees of timing would have to be taken out – and the factory computer won’t do it. Generally speaking, timing should be retarded 2 degrees for every 50 horsepower of nitrous power.
The performance of the 75-horsepower baseline is somewhat misleading, as the nitrous system doesn’t simply add 75 additional horsepower across the rpm range. Because engines make different horsepower and torque at different rpm levels, based on airflow and other factors, the nitrous-boosted engine simply does the same. As for the practical limits of the Hemi engine, it’s pretty durable. In stock trim it can generally handle more nitrous than allowed by the computer’s limitations. That said, however, both the 5.7L and 6.1L engines have cast pistons. They aren’t as hard or durable as forged pistons and would likely be the weak point with sustained, high-horsepower hits of nitrous – more than could be handled with the stock computer.
Dedicated kits marketed specifically for Hemi-powered vehicles were few. Luckily, the basic components of all nitrous systems are, for the most part, universal – such as the ZEX system used in this story. They include a storage tank for the nitrous (usually a 10-pound bottle), braided steel lines to carry the nitrous, activation solenoids, a fuel line tie-in and activation switches.
An advantage of the Hemi – car, pickup or SUV – is its electronic throttle control, which eliminates the need for a micro-switch to be installed near the throttle. Instead, the nitrous system’s activation switch can be spliced into the throttle control wiring harness. By tying in to the throttle position sensor (TPS) output voltage wire, the TPS voltage signal determines when the nitrous system engages – below wide open throttle, no activation; at wide open throttle, the nitrous system engages.
The biggest hassle with a “general” kit, such as the one used in the installation outlined here, is the trial-and-error procedure required to determine the correct TPS voltage wire among the numerous wires in the electronic throttle’s wiring harness. This is done by depressing the throttle pedal with the power on and the engine off. A handheld voltmeter is used to test the wires in order to determine which one is the correct voltage output carrier. Determining the correct TPS voltage wire requires manual activation of the throttle blade while testing a wire with a test light and depressing the pedal. Once the TPS voltage wire is located, a connection from the nitrous controller simply attaches to the wire and enables the wide-open throttle activation.
From there, an instant rush of power is just a press of the throttle away.
Editor’s note: This story is excerpted from author Barry Kluczyk’s new book, “New Hemi High-Performance Builder’s Guide,” from CarTech Books (www.cartech.com).
Paul’s High Performance
3715 Commerce Street
Jackson, Mich. 49203
3418 Democrat Road
Memphis, Tenn. 38118