We’ll admit that we can’t leave a perfectly good car alone, no matter what it is. For instance, let’s say that you hand us a low-mileage 2004 V6 Mustang. It gets good mileage, it’s reliable, and with a whopping 195 horsepower at the brochure from the 3.9l V6, there’s absolutely no temptation to spontaneously enter the Stoplight Grand Prix while commuting to work. Normal people would enjoy the Chick ‘Stang for what it is, but we’re not normal by any standard, so we immediately began to look for ways to hop it up. Of course, it makes no sense to spend a lot of money and time just to make a V6 that can beat a GT, so our focus was on getting the biggest bang for the buck possible, without ruining the car’s basic drivability and gas-sipping economy. To make that happen, we enlisted the help of our friends at Zex and K&N.

A Breath of Fresh Air

Going with K&N was a slam-dunk; putting an intake kit on is one of the easiest and quickest ways to free up some extra horsepower, and K&N brings OEM-level engineering resources to the table with their systems. For most applications, K&N offers several options, with the most basic being a replacement filter for the stock airbox. For those who have mastered the challenge of using a screwdriver and socket wrench, it’s only slightly more difficult to swap on one of their full intake kits, which come in two different flavors.

The Typhoon series uses mandrel-bent aluminum tubing, while the FIPK (Fuel Injection Performance Kit) series are made from roto-molded high density polyethylene. What’s the difference? K&N says that while a lot of customers prefer the polished “CAI” look and style of the Typhoon intake, generally speaking, the FIPK intake will provide slightly better power gains, due to the fact that the designers have more freedom to tune the shape and dimensions of the plumbing.

In our case, FIPK part number 54-2532 was the right call – According to K&N, with the earlier 3.8L V6, this intake makes just shy of seven additional horsepower at 4825 RPM, and it’s CARB-legal for use in California on street-driven vehicles, an important consideration for this daily driver.


K&N’s Fuel Injection Performance Kit is one of the quickest and easiest ways to free up horsepower for just about any car or truck.


The FIPK re-uses the stock MAF sensor, and is engineered to provide maximum flow while avoiding the dreaded “check engine” light. All of the components in the kit are OEM-quality, and the whole intake swap takes less time than watching an episode of “Lost” (and is far less frustrating).

Off with the Old, on with the New

As we expected, installing the FIPK took less than a half-hour from start to finish, and went in like a factory part, with no tweaking required. Better yet, the new intake tube gave us a place to install the nozzle for the second part of our upgrade, the Zex wet nitrous system. When it comes to a horsepower-per-dollar calculation, there’s simply no other mod that can keep up with nitrous oxide. With a street price of just under $650, the Zex kit we installed, part number 82217, can be jetted for anywhere between 75 and 175 horsepower. Since we’re not totally insane, we also ordered up a set of 50-horsepower jets to start with – more on that in a bit.


The K&N intake tube provided an easy place to mount the Zex nozzle, just past the mass airflow sensor. Because it’s a “wet” system, the smooth inner surface of the molded polyethylene tube won’t trap fuel like the stock corrugated rubber one would.

Wet vs. Dry

Nitrous systems come in two different flavors – “wet”, which inject both fuel and nitrous through one or more nozzles or spray bars, and “dry”, which spray only nitrous and depend on one of several different methods to add the requisite additional fuel through the stock injectors. Dry systems are generally easier to install and have the advantage of not putting any fuel through the upper intake tract, which in our car is quite complicated and obviously not designed to smoothly and evenly deliver anything denser than air. On the other hand, wet systems generally have more power potential and don’t run the risk of overwhelming the stock injectors’ ability to provide fuel, and are easier to tune with nitrous and fuel jet changes. In our case, the fact that the ’04 uses a “returnless” fuel system with computer-controlled pressure at the rail made a wet kit a necessity.


One of the components that makes the Zex kit so easy to install is this adapter that sandwiches between the fuel rail and fuel pressure sensor, and provides an easy way to tap in without cutting any lines.

A Custom Fit

Zex’s 82217 kit is designed specifically for 1999-2004 2- and 4-valve Modular Fords, which use the same fuel pressure sensor and fitting as our V6, making it perfect for our needs. The billet aluminum fuel rail adaptor in the kit sandwiches between the sensor and the rail, and provides an easy way to supply fuel to the Nitrous Management Unit without any cutting and splicing. Speaking of the Nitrous Management Unit, in addition to taking the place of the pair of solenoids, relay, and WOT switch required in a conventional nitrous system, the NMU has a built-in Throttle Position Sensor adaptor that taps into the stock TPS signal with a single wire, and learns the voltage curve with a simple one-button programming process. The NMU will only activate when it senses that the throttle is all the way to the floor, and wiring it up and programming it is far, far easier than trying to rig up a microswitch on the throttle body like a typical kit requires.


The Zex Nitrous Management Unit puts all the solenoids and electronics in one compact box, and it incorporates a built-in throttle position sensor interface that can be calibrated to the output from your stock TPS so that the system only activates at wide-open throttle.

Safety First

To complete our installation, we also ordered up Zex PN 82085, the Traction Control Window Switch. In any nitrous setup, a window switch, which prevents the system from activating until a target RPM is reached, and shuts it off when a second RPM limit is exceeded, is a good idea. To make sure we got vroom instead of boom, we wanted to prevent the system from kicking on until 3,000 RPM, and turn off before the engine hit the stock rev limiter at 5,250. Window switches have been around for a long time, first as boxes that required RPM “pills” to set the high and low limits, then with dials to adjust the settings. The Zex Traction Control Window Switch kills older designs stone cold dead – an LED display and two buttons make programming it easy.

The first step is configuring it for how many cylinders you have, and what kind of ignition system you’re using. It can handle from 1-12 cylinders, and distributor, coil-on-plug, or wasted spark ignitions, and the input trigger works with any pulsed 12-volt signal. In our case, we picked it up from one of the wasted-spark coil pack triggers. When the window switch is powered up and the engine is running, the LED displays the current RPM, so you can confirm that it’s reading it properly – a huge advantage when you’re setting it up.


No nitrous system should be without a window switch for safety, and Zex’s Traction Control Window Switch is easy to set up and incorporates an optional “skip shift” function to delay nitrous activation until you’re out of first gear to control wheelspin.

Under Control

The window switch has one additional trick up its sleeve – you can also program it to skip activation until it’s seen its upper limit reached, meaning that you can automatically lock out first gear and only spray once you’ve reached your target lower RPM in second, which is where the “traction control” aspect comes in. If you’re still getting wheelspin in second, you can set it up to skip the first two gears, or in fact, any number of gears you want. We left this feature turned off, since we’re already hooked up and out of the hole by the time the tach passes 3,000 RPM.


The installed intake and nitrous system are inconspicuous under the hood, and will be even harder to notice once we loom up the wiring. First, though, let’s hit the rollers and see what we gained.


We used Sniper’s tuning software and interface box to adjust our Mustang’s timing map for safety, taking out 2 degrees of advance across the board. The Sniper hardware and software also allowed us to datalog all the ECU parameters during our dyno runs.


The end result of an easy day’s work was a jump from 152 rear-wheel horsepower stock, to 160 with the K&N FIPK installed, and that was before we turned the bottle on.


With the nitrous flowing, we saw 203 ponies and 285 pound-feet of torque on the dyno with the small 50-shot jets. At the dragstrip, we went from a previous best of 10.592 at 66.83 MPH in the 1/8-mile all the way down to 9.869 at 75.29 – that translates to more than a second quicker in the 1320, and we haven’t even tried out the 75-shot jets yet…

We started this project with the intent of adding meaningful horsepower and dropping our ET without spending a lot of money or time or killing our Mustang’s street manners, and we scored on all counts. As always, K&N’s FIPK is about the easiest DIY upgrade you can do, and we have to say that Zex’s nitrous system is about as foolproof and simple to install as any kit we’ve ever put on a car, and we’ve done a lot of them! With the addition of the Traction Control Window Switch, we can safely put more than 200 horses to the wheels at the flip of a switch, while keeping the engine’s stock economy and durability intact for day-to-day driving.