NOS Three-Valve Kit Test - Liquid Displacement

A pretty strong case can be made for Ford's modern Mustang machinery. While we all look back fondly on the musclecar era of yesteryear, the reality is that nostalgia has altered our perception somewhat.

Who doesn't love a thumping Cobra Jet fastback or a high-winding Shelby small-block? As great as these classics are, time and technology have marched on so that a modern modular motor not only offers every bit as much performance (actually more), but it does so while delivering a combination of driveability, fuel economy, and reduced emissions only dreamed of by their carbureted counterparts.

I don't think its sacrilegious to say that the current 4.6L offerings are the most powerful (and impressive) Mustang powerplants ever offered. That the new 5.4L GT500 motors offer over 540 hp (550 hp in the now-defunct Ford GT) while still managing to knock down as much as 25 mpg on the freeway--I know this firsthand from a recent cross-country trip--is a testament to the new design. The GM boys used to cry foul and say Ford had to resort to forced induction to achieve these numbers, but just look at what's powering the new ZR1.

Nevertheless, there are always ways to improve power output, right? Forced induction is one route, as are basic bolt-ons. Yet another route, pioneered by the German Luftwaffa and made popular by street racers across the nation, is nitrous oxide. Originally designed to enhance the power output, (and therefore, the flight ceiling), many German (and later, British) pilots relied on the power-enhancing compound for their very lives: Winning bragging rights or even a fist full of cash at some street race hardly compares to the rush of saving your hide and living to fight another day.

For those modern Mustang owners unfamiliar with nitrous oxide, the compound contains both nitrogen and oxygen (similar to the air you and your motor already breathe). It is actually the oxygen contained in the nitrous-oxide compound that is responsible for the additional power.

Blame both TV and movies for the common misconception that nitrous oxide is highly explosive or even flammable. It would take a nitrous bottle stuffed to the regulator with C4 explosives to produce the kind of explosions seen on the big screen. The door-blowing explosions and singed eyebrows accompanied by fireballs that send the aforementioned street racer's ride to a fiery grave are noticeably absent.

It should be noted that the oxygen in the nitrous-oxide compound is extremely flammable--the compound itself is not. Only after the oxygen molecules have been released from the nitrogen compound will they be allowed to burn. Fortunately for enthusiasts, it requires a great deal of heat (to the tune of 572 degrees) to liberate the oxygen molecules. This tremendous oxygen-liberating temperature is supplied by the combustion process. Technically speaking, nitrous oxide is not a fuel, but rather an oxidizing agent. Once released, the free oxygen molecules support (or enhance) the combustion process, which requires the burning of some other fuel--in this case, gasoline.

If the release of the power-producing oxygen molecules isn't enough to win you over, additional power gains are realized by the reduction in inlet-charge temperature. For automotive use, nitrous is stored under pressure as a liquid; when injected into the engine, 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 (the inlet air). Though we normally associate a boiling point with heat (converting liquid water to steam at 212 degrees), the boiling point of nitrous oxide is a chilly -129 degrees.

In addition to the heat absorbed during the boiling process, introducing a compound at -129 degrees has an additional positive (chilling) effect on the inlet-charge temperature. Cooler inlet air is rich in oxygen molecules. Basically speaking, the cooler the air, the greater the number of oxygen molecules present. Nitrous oxide is about as cold a substance as you will ever deliver to your motor. Not surprisingly, the combination of extra oxygen molecules and additional cooling can produce some pretty impressive power gains.

One of the great things about nitrous oxide is that the additional power supplied by nitrous injection is nearly independent of the power output of the original motor. You don't need a dedicated nitrous motor or even anything more exotic than a stock motor to enjoy the benefits of nitrous.

We mention that the nitrous oxide is responsible for cooling the inlet charge, something that both improves power output and helps suppress harmful detonation. The separation of the nitrogen and oxygen molecules (during combustion) into individual components also helps to minimize detonation. This built-in detonation control allows impressive power gains without fear of damage to the motor, even on a stock motor with cast pistons. Of course, the power gains and life expectancy of the motor are directly related to the tune, as proper air/fuel mixture and (especially) ignition timing are critical on a powerful nitrous motor. Applied and tuned properly (as per the supplied instructions), a modern nitrous system can provide safe, effective, and reliable power gains. In fact, a good nitrous kit (in this case, from NOS) will make your 4.6L motor feel like it just gained a few extra liters of displacement.

While nitrous oxide will definitely wake up a stock Three-Valve, there are ways to further improve the power of a nitrous motor. With so many additional oxygen molecules finding their way into the combustion chamber, they naturally have to find a way out. This is where cam timing can play a part, as altering the exhaust lift and duration relative to the intake will help aid in ridding the combustion chamber of all those previously beneficial oxygen molecules.

While a cam swap may well net additional power on a nitrous motor, the 4.6L Three-Valve came factory equipped with variable cam timing. This means it's possible to alter the cam timing to help improve the output once the nitrous is injected.

This is usually most beneficial with large doses of nitrous, and since our stock motor is only going to see a 75hp shot, we decided to simply run the system without altering the cam timing. This is how 99 percent of the users will run the system, so we want to illustrate the gains offered under these conditions.

Given the stock nature of the modular test motor, the fact that it doesn't belong to us, and our desire to perform all testing on 91-octane (California premium unleaded) pump gas, we kept the nitrous shot purposely conservative at 75 hp. We figure this combination is something that can easily be duplicated by your average (daily driven) street '05-up GT.

The motor was equipped for (engine) dyno use with a FAST engine management system and 36-pound injectors. The FAST XFI management system allows us to dial in the timing and fuel curves to optimize the power produced by stock trim with the nitrous.

Actually, there was very little tuning required with the wet nitrous system from NOS (PN 02121NOS). All we had to do was ensure that the bottle pressure was at 900 psi, and we were rewarded with slightly more than the advertised power gains. We tuned the combination to produce a 13.0:1 air/fuel ratio and 30 degrees of total timing (more or less timing produced less power). Equipped as such, the 4.6L produced 359 hp and 381 lb-ft of torque before activating the nitrous.

Before engaging the NOS wet EFI kit (equipped with 75hp jetting), we retarded the timing by 3 degrees to reduce the chance of detonation. This dropped the power output to 351 hp. Activating the NOS fogger system increased the peak power output to 427 hp at 5,700 rpm, while the torque peak shot up to 468 lb-ft of torque (see the graph for full details). The nitrous improved the peak power output by 68 hp and torque by 87 lb-ft, but the gains were consistently 75 hp or better through the entire rev range (once activated).

Had we elected to run the nitrous clear past 6,000 rpm, we'd have seen an even higher peak-power number. And believe me, you'll notice an extra 75 hp--and especially 87 lb-ft of torque.

Stock 4.6L Three-Valve vs. NOS Nitrous (75hp shot)
As is evident by the power numbers, installation of the NOS wet EFI nitrous system offers a significant increase in power and, more importantly, torque. The 4.6L test motor was equipped with a set of long-tube headers and run without any of the accessories--only an electric water pump--and at a cooler temperature (130 degrees); this is why the motor produced so much more power than the 300hp factory rating. Run in stock trim, the 4.6L motor produced 359 hp and 381 lb-ft of torque. Since we are running the motor on 91-octane pump gas, we elected to retard the timing by 3 degrees before engaging the nitrous. Running a 75hp shot, the NOS kit improved the power output to 427 hp and 468 lb-ft of torque. We made sure the nitrous bottle pressure was at 900 psi for optimum nitrous delivery before making our runs.