Richard Holdener
December 18, 2006
Project Redheaded Step Child was finally going to get a serious power infusion in the form of nitrous oxide.

Project Redheaded Step Child is still going strong, but in our attempt to make 300 rwhp with a naturally aspirated 4.6, every last horsepower is getting harder and harder to come by. While there's a new, dedicated non-PI intake waiting in the wings, we decided what the motor really needed to play ball in the big leagues was a serious dose of steroids. With all the talk about juicing, we decided to jump on the bandwagon and let it flow.

Sure, some may see it as taking the easy way out, but we've just about run out of all-throttle-and-no-bottle options on our early Two-Valve 4.6. Remember, the plan was to achieve 300 rwhp without resorting to increasing displacement.

With a stroker out, we decided this was an excellent time to experiment with a powerful substance capable of providing super power to our otherwise mild-mannered Clark Kent of a mod motor. While much has been written about nitrous oxide in the pages of MM&FF, know that the chemical compound is actually not a true fuel, but rather an oxidizer. Other than in the mythical realms of TV and cinema, nitrous oxide does not explode into flaming fireballs of death, not unless your nitrous bottle happens to be sitting precariously close to a stack of C4 explosives.

In internal combustion applications, nitrous oxide was originally used when the Germans (and British) went searching for ways to improve the power output, and therefore effective ceiling, for their military aircraft during World War II. What better incentive can there be for the go-fast juice than having someone shooting at you? Today, the compound is most commonly used as a general anesthetic in the dental industry. Hot rodders-and many professional racers-know the substance for its effect on the power production of the internal combustion engine.

As indicated previously, nitrous oxide is a compound consisting of both nitrogen and oxygen, not unlike the air we currently breathe. From a performance standpoint, it is the oxygen molecule that we are most interested in, as oxygen supports the combustion process. Naturally the combustion must be supplied enrichment fuel, but this is taken care of by the nitrous system.

The Zex Wet EFI kit included everything needed to install the kit on our '96 4.6 Two-Valve engine. The only thing we had to do was fill the bottle (they must be shipped empty).

While it may seem that having the extra oxygen molecule makes nitrous flammable, the reality is that the extra molecule becomes available only once it has been released from the compound. This release takes place in the combustion chamber when the temperature exceeds 572F degrees. Once the temperature has released the oxygen molecules, they are free to support the combustion of the additional fuel. The result is a dramatic increase in power. It is possible to double the power output of your stock motor with the use of nitrous, but typical power gains are on the order of 75-125 hp for most street Mustangs.

The limiting factor will be the strength of the engine, the flow rate of the nitrous system itself, and the tune. Obviously the greater the desired power increase, the more critical the air/fuel and timing curves become. Run the motor a tad on the lean side when you add a 75hp shot to your 300hp motor, and you're likely to get away with it. The same mistake with a 200hp shot and say goodbye to your motor-forged pistons or not. Truth be told, missing the air/fuel ratio is a lot less detrimental than the timing curve, which is why companies like Zex supply recommendations to retard the timing for specific hp gains.

For Project RSC, we chose the Zex EFI Wet nitrous kit (PN 83023). The wet kit was so named because the system combined the nitrous and additional fuel enrichment into a single (common) fogger nozzle. The Zex wet kit is adjustable, with jetting available to increase the power increase from 75 hp to 125 hp. It came complete, offering everything from the 10-pound (empty) bottle down to the smallest mounting screw and electrical connector. Also included in the kit was the patented Zex Active Fuel Controller. The controller automatically adjusts the fuel enrich-ment supplied to compensate for the changing bottle pressure. Naturally, the higher the bottle pressure, the greater the nitrous flow.

Replacing the conventional mechanical full throttle switch was wiring to the TPS sensor. The fuel con-troller will actually learn your TPS voltage curve to allow nitrous activation only under full throttle.

This change in nitrous flow (from heat and use) can alter the power supplied, to say nothing of the air/fuel ratio. The trick Active Fuel Controller adjusts for this change in bottle pressure to help optimize power production. In addition to the regulatory duties, the Active Fuel Controller featured a patented electronic TPS switch. The controller actually has the ability to learn the TPS voltage curve of your motor and will only activate once the maximum (acceptable) TPS voltage is reached. This ensures the nitrous will never be activated at part throttle. Too little throttle angle or engine speed can create a backfire situation-definitely something to be avoided with the factory composite intake manifold.

According to Zex, its EFI Wet System also features a unique fogger-nozzle design. Like other systems, the fogger nozzle was designed to combine both fuel and nitrous into the motor, but the Zex fogger has a pair of important features to further improve both atomization and safety. The first advantage offered by the unique fogger was Fuel Shear technology. The fogger nozzle featured a transfer tube to directly inject fuel into the highest velocity area of the nitrous plume. The high-speed nitrous gas shears the fuel away from the transfer tube, thereby maximizing the atomization. The greater the atomization, the better the fuel distribution among cylinders. This was ultra-critical when injecting the nitrous/fuel combination into the long-runner EFI intake on our '96 GT. In addition to Fuel Shear, the nozzle also features Active Fuel Control. The design of the fogger nozzle creates a vacuum across the top of the fuel transfer tube. As the speed of the nitrous flow changes (from changes in bottle pressure), the vacuum created also changes. This change in vacuum across the fuel transfer tube increases or decreases fuel enrichment to further optimize safety and performance.

Installation of the Zex kit was fairly straightforward, including mounting the bottle in the trunk (make sure you don't drill a hole in the spare tire-we speak from experience here), drilling and tapping the air inlet tube for the fogger nozzle, and mounting the fuel controller in the engine compartment. The Zex kit included the necessary fitting to replace the factory Schrader valve to act as a fuel supply to the fuel controller. With the fuel and nitrous feed lines connected to the controller, all we had to do was run the pair of nitrous and fuel lines from the controller to the fogger nozzle.

We made sure to insert the 46 nitrous jet and 30 fuel jet to supply our desired 100hp nitrous shot-a safe level running 91-octane pump gas. The arming switch (to activate the system) was located inside the car (hidden away in the unused ashtray), while the activation switch was actually the TPS switch in the fuel controller. We chose a momentary activation switch as it was possible to activate the nitrous at low engine speeds (since activation only required the arming switch and full throttle). We like running full throttle at lower engine speeds than 3,500 rpm-a safe activation rpm for nitrous-so we decided to activate the nitrous manually with a momentary switch. The TPS switch in the fuel controller made sure activation could happen only at full throttle, but we were free to manually select the activation rpm.

Before testing, it was necessary to go through a learning sequence for the active fuel controller, to allow the system to learn the TPS voltage curve. This required turning on the ignition key (but not starting the motor) and then turning on the fuel controller. We then pushed down the gas pedal to full throttle and held it there for 10 seconds to allow the controller to learn the full-throttle voltage supplied by our TPS. After that, a quick check revealed all systems were go.

This button was used to initiate the learning mode on the controller. After switching everything on, we simply pushed down the throttle for 10 seconds, and the controller recognized the full throttle voltage of our system.

Before heading to Westech for testing, we took the liberty of requesting a switch chip from Steve Ridout at Powertrain Dynamics. He set us up with a dual-position chip that allowed us to run two programs. Program 1 was the standard program, while program 2 retarded the total timing by 3 degrees in anticipation of the nitrous. The instructions supplied by Zex recommended retarding the timing by 3 degrees at this power level (on pump gas), so we heeded this advice.

Run in baseline trim (no nitrous), the 4.6 produced peak numbers of 274 rwhp at 5,200 rpm and 316 lb-ft of torque at 4,200 rpm. Activating the Zex nitrous kit bumped those figures to 377 hp and 497 lb-ft of torque. The gains offered by the 100hp shot were great at 131 hp and 182 lb-ft.

We can't wait to see how it feels on the street against some unsuspecting Camaro.

Project RSC: Naturally Aspirated vs. Zex 100hp Nitrous
Finally, Project RSC was going to have some street credibility. Though powerful for an early 4.6 at 274 rwhp, it had to resort to the juice to make major-league power. All it took was a simple, 100hp shot from a Zex wet fogger system, and our 274 rwhp jumped to 377, while the peak torque skyrocketed from 316 lb- ft to 497. Yes, we missed the 500 lb-ft mark by just 3. Note the billiard-table-smooth power curve, reaching 375 hp at 4,300 rpm and never dropping below that point (or exceeding 377 hp) for nearly 2,000 rpm.