A steady steam of nitrous oxide adds plenty of power, but what actually happens to the airflow through the motor?

Words and Photos By: Richard Holdener

Just like death and taxes, there are certain things in the automotive world we know to be true. The internal combustion engine has long been likened to a giant air pump. The more air you put into the motor, the more power it will put out. It’s just simple science. Performance modifications that increase airflow include displacement, ported heads, and more aggressive cam profiles. Also included are intake manifolds, larger carburetors, and all forms of forced induction, like turbos and superchargers. All of these components seek to increase the airflow into the motor to increase the output. In truth, long-tube headers can be added to that list, as they perform the same operation. Tuned headers just go about it through exhaust scavenging that increases intake flow into the cylinder. Airflow seems to be the key to power production, but what if we told you there was a power adder that increased power while decreasing airflow? Enter nitrous oxide.

Contrary to popular belief, nitrous oxide is not a fuel, but rather an oxidizer. You can blame the movies and TV for the confusion, but nitrous oxide does not burn nor is it likely to explode in spectacular fashion; those are special effects. What really happens when you open the bottle of nitrous and touch a match to the spray is much less exciting. The flame in question is simply — and quickly — extinguished. There are no thunderous explosions, no massive fire balls, just an anticlimactic wisp of smoke as the flame was extinguished by the high-pressure, ice-cold stream of nitrous oxide.

The result of the match test begs the question, if nitrous oxide doesn’t burn, how then, does it increase the power output of the motor? Nitrous oxide adds power by releasing free oxygen molecules contained in the compound. Since oxygen molecules are a key ingredient in power production (the more oxygen present, the greater the power potential), the release of these oxygen molecules adds to the power output of the motor.

Nitrous oxide increases the power output of the motor by another method as well. Nitrous is stored under pressure in a liquid state. Once injected into the inlet tract from the pressurized bottle, the liquid nitrous quickly turns into a gas. The transformation of a compound from a liquid to a gas is a process called vaporization. This liquid-to-gas vaporization requires an input of energy; in this case, the energy is heat.

The vaporization of the liquid nitrous absorbs heat from the surrounding inlet air, something desirable in any performance application (think of it as a chemical cold air kit). While we associate heat with boiling (for example, water turning from a liquid to a gas), the vaporized nitrous does not produce heat, at least not to the inlet air. Though vaporized, the temperature of the nitrous oxide is still at or near -129 degrees (the boiling point of nitrous oxide). Naturally, mixing your inlet air with a gas measuring a chilly -129 degrees provides a dramatic cooling effect. It is this double cooling that not only increases the density of the inlet air, but also reduces the chance of detonation, both good.

Now that we understand more about nitrous oxide, we can get to the test. The question for this adventure was what happens to the all-important airflow into the motor when we introduce nitrous oxide. We know that properly applied, nitrous oxide can yield substantial power gains, but do the gains come from increased airflow? To find out, we set up a small-block test motor with a Zex Perimeter Plate nitrous system, then installed the Super Flow air turbine to data log the airflow. The 372 stroker small block included a Dart block stuffed with JE forged pistons and Total Seal rings. The gang at Westech Performance upgraded the short block with a Crane hydraulic roller cam, AFR Eliminator heads, and an Edelbrock Super Victor intake. Also present were an MSD distributor, Holley 950 Ultra XP carb, and TCI damper. The motor was set up for the dyno session with a Meziere electric water pump, 1-¾-inch long-tube headers, and a fresh (Milodon) pan full of Lucas 5W-30 synthetic oil.

Given the data logging offered by the flow turbine on the dyno, the airflow test was a simple one. All we had to do was run the motor with and without nitrous and measure the change in airflow. Run on the dyno without nitrous, the normally aspirated small block produced 524 hp and 465 lb-ft of torque, with airflow readings that started at 369 cfm and rose to a peak of 684 cfm at 7,000 rpm. After injecting the 150-hp shot from the Zex Perimeter Plate system, the peak power numbers jumped to 689 hp and 593 lb-ft of torque.

The impressive thing is that the big power gains came with a decrease in airflow, as the peak turbine reading with the nitrous registered just 618 cfm. The injected nitrous displaced some of the airflow, but the extra oxygen molecules more than made up for the loss in airflow. This is why nitrous motors traditionally run big port volumes (both intake and cylinder head), to offer extra flow capacity for huge doses of the sweet stuff.

Sources: AFR, Airflowresearch.com; Crane Cams, Cranecams.com; Edelbrock, edelbrock.com; Holley/Hooker, holley.com; JE Pistons, jepistons.com; Lucas Oil, Lucasoil.com; MSD, Msdignition.com; TCI, TCIauto.com; Total Seal Rings, Totalseal.com; Zex, www.zex.com.