Dale Amy
March 12, 2007

Horse Sense: Though it seemed fairly obvious to us, we thought we'd better check with Zex sources who confirmed that, although this kit (PN 82034) was originally advertised specifically as being for the S197 GT, it installs and works equally well on the 4.0.

We've already reported how well the S197's 4.0 V-6 seems to like boost. Now it appears the SOHC six is just as enthusiastic about nitrous, as Paul Svinicki found out when he plumbed Zex's S197 Mustang GT kit into his Paul's High Performance '05 V-6, with dramatic results. How about a 12.80-second pass at 109 mph on an 84-degree day with a 26-mph headwind? This was more than a full second quicker and 12 mph faster than the car's best naturally aspirated run-not bad for a 75hp shot on a V-6.

Jamie Meyer, our resident mad doctor, reported on the installation of an identical Zex kit on an '05 GT in our Feb. '06 issue ("Spray Pattern," p. 102), so the hardware should look familiar. In case you missed that one, some of the interesting highlights of Zex's S197-specific kit include a Nitrous Management Unit that monitors the new Mustang's electronic throttle-control circuitry to precisely determine a wide-open throttle condition, a fuel-rail adapter to easily access fuel for the nozzle, along with a selection of jets for 75 to 175 hp. Zex's nozzle design also has active fuel control that is said to ensure proper air/fuel mixture by monitoring nitrous bottle pressure and adjusting fuel enrichment accordingly. Another neat feature for those of us who are, well, electrically challenged is the option of using a nitrous-arming switch that simply plugs into your 12V power point (also known as a cigarette lighter in less politically correct times).

The kit was already installed on PHP's racer at the time of our visit, so this isn't a follow-along how-to, though you'll see from our photos and captions how Zex can suggest the kit might be installed in as little as a couple of hours. A glance at our dyno sidebar should be convincing that it will be time well spent.

Arrayed from left to right in front of the distinctive purple bottle are the fuel-rail adapter, nitrous/fuel nozzle, bottle-pressure gauge, and the oh-so-wise nitrous management system. These items form the guts of Zex's S197 Mustang kit and are just some of the big stuff. The kit is utterly comprehensive in content, and we applaud the company's thorough and easy-to-follow instructions. Expect to pay around $620, plus about another C-note if you'd like a bottle warmer.

Two choices of arming switches are included: the traditional shielded toggle on the left-that requires connection into an underdash circuit capable of handling the system's 10-amp solenoid draw-or the slick little setup on the right that simply plugs in and draws power from the cigarette lighter.

The kit brings along five different nitrous and fuel jets for a 75-175hp hit spread. The 75 shot's a no-brainer; Zex says it doesn't even dictate any timing retard assuming use of premium fuel on a stock calibration. Going to any of the larger jets certainly requires recalibration at the least, and possibly fuel-system upgrades. In other words, proceed carefully.

The brains of the system, along with the solenoids, lie within the Nitrous Management Unit. The black button and LED visible on the side of the unit are used during installation to program the unit's WOT-activation switch, basically allowing the NMU to learn the electronic-throttle-control circuit's voltage curve to precisely plot wide-open throttle.

The combination nozzle is clearly marked for insertion of the respective nitrous and fuel jets, which are all clearly numbered. We just stuck in a random pair for photo purposes, but Zex's instructions include a chart setting out the correct jets for the desired horsepower level. PHP used the smallest (75 hp) combination of jets. Notice the threaded area on the body of the nozzle...

...that's used to thread either directly into a metal inlet duct as fitted to PHP's car (part of PHP's V6 cold-air kit) or into an included bulkhead fitting for use with the factory rubber inlet duct. The supplied -3 AN lines are routed to the nozzle from the outlet side of the nitrous-management unit.

The most practical place to mount the nitrous-management unit is somewhere along the driver-side inner fender apron forward of the strut tower. This way, the kit's quartet of braided lines will reach their intended targets. Smart as this setup is, only three wires protrude from the NMU: black goes to chassis ground, red connects to the power wire from whichever of the included interior arming switches you decide to use, and white taps into one of the electronic throttle-control wires using a supplied T-tap. Nice and simple.

The most practical place to mount the nitrous-management unit is somewhere along the driver-side inner fender apron forward of the strut tower. This way, the kit's quartet of braided lines will reach their intended targets. Smart as this setup is, only three wires protrude from the NMU: black goes to chassis ground, red connects to the power wire from whichever of the included interior arming switches you decide to use, and white taps into one of the electronic throttle-control wires using a supplied T-tap. Nice and simple.

PHP chose the simplest arming-switch option-the one that plugs into the 12V power point on the dash. One of its two wires goes to ground, while the power side is passed through the firewall to connect to the aforementioned red wire from the NMU.

Doesn't look like it should produce 280 hp, does it? Check out the torque numbers on the dyno chart.

Some notes on the dyno numbers. First, the baseline pull was made with PHP's V-6 airbox, A/C bypass belt, alternator, underdrive pulley, and tune, along with JBA short-tube headers and dual exhaust kit. Those were the powertrain mods that permitted the coupe to run 13.9s prior to the nitrous. Second, the reason for the fairly narrow rpm window charted is that as Paul engaged the nitrous at about 2,800 rpm, the V-6 instantly spun its tires on the rollers-despite being firmly strapped down-and didn't settle down until about 4,100 revs. This stuff hits hard. We were using the 75hp jets and ended up with almost exactly that amount of peak horsepower gain. In typical nitrous form, however, the torque gain was monumental.

RPM Baseline Zex Nitrous Difference
Power Torque Power Torque Power Torque
4,100 182.5 233.7 279.3 357.7 94.7 112.9
4,{{{200}}} 186.1 232.7 277.2 346.6 88.4 102.6
4,{{{300}}} 189.6 231.6 274.5 335.3 81.7 92.2
4,400 192.9 230.2 271.3 {{{323}}}.8 75.2 82.7
4,500 196.1 228.8 268.1 312.9 71.2 76.4
4,{{{600}}} 198.7 226.9 267.3 305.2 68.2 71.4
4,700 201.2 224.8 266.9 298.3 65.3 66.8
4,800 203.0 222.1 266.5 291.6 {{{62}}}.4 62.3
4,{{{900}}} 204.3 219.0 265.4 284.4 59.5 58.1
5,000 205.4 215.7 263.8 277.1 58.4 61.4
5,100 205.9 212.0 262.8 270.6 56.9 58.6
5,200 205.9 207.9 261.7 264.3 55.8 56.4
5,300 205.5 203.6 259.6 257.2 54.1 53.6
5,400 204.2 198.6 257.1 250.1 52.9 51.5
5,500 203.2 194.0 254.1 242.7 50.9 48.7
5,600 200.7 188.3 250.9 235.3 50.2 47.0
5,700 198.5 182.9 248.0 228.5 49.5 45.6
5,800 195.1 176.7 243.8 220.8 48.7 44.1
5,900 192.2 171.1 238.4 212.2 46.2 41.1
6,000 188.1 {{{164}}}.6 235.9 206.5 47.8 41.9