Zex Appeal

Today's Mustang fans are eager for hot items and the latest technology. There's been a lot of focus on the Modular-motored Mustangs and for good reason. A mildly-modified '99-up GT or a stock Cobra can run easy 12s and this is good for the consumer, but at the same time the ante has been upped for the aftermarket manufacturers who must produce more efficient parts to get these cars in the 11s or 10s. Most manufacturers are aware of this, but they also know they're dually challenged. They must produce components that improve horsepower and/or handling, yet without negatively effecting driveability. Perhaps that's why nitrous oxide has been one the best bolt-ons for those who need an extra punch. With nitrous oxide you don't give up any driveability, because you can easily add 100-175 horsepower and then close the bottle for that trip to the mall. Nitrous can be that simple.

Lately, there have been a few new juice kits to hit the market for the 4.6 Mod motors, and this has made the 5.0 faithful feel neglected. Well, fear not 5-liter brethren; we are on your side and we have a new way to get you up to speed. During a recent trip to Memphis we learned that ZEX has a new nitrous kit designed for the 5.0, so naturally we had to get jugged. ZEX nitrous systems have been around for a few years, but the first kits were designed for the sport compacts and/or the newer fuel-injected models including the 1996-98 4.6-liter Mustangs (which MM&FF covered in the March 2000 issue--see "Hot And Easy ZEX").

ZEX nitrous kits take the pain out of a typical nitrous install because the solenoid, activation switch and wiring is all compacted into one small attractive box called the Nitrous Management Unit. You only need to mount the bottle, connect a few wires, tap into the throttle body and you're flying. "We saw the need for a simple nitrous kit that anyone can install," says Matt Patrick, the product manager and engineer at ZEX. "We do all the assembly and this eliminates the need to mount wide-open throttle micro-switches, mount solenoids or even use messy thread sealer. We also test every unit with two in-house redundancy tests so the customer is assured that the unit is going to work."

The NMU is the brain of the system. Not only does it save time during set-up, it has features that will simplify nitrous use for the beginner. For instance, after being armed with a toggle switch, the system is activated by a signal from the throttle position sensor (rather than the typical micro-switch), which, in turn, activates the nitrous solenoid located in the box. And this is all done with one simple connection to the TPS output voltage wire. In addition, the system is "dry", meaning only nitrous flows through the manifold and the additional fuel is fed through the injectors.

More importantly, "The ZEX system bleeds off a small amount of nitrous pressure to the NMU so it has a constant and correct reference to bottle pressure. This allows the system to constantly adjust or trim the fuel enrichment to achieve peak nitrous-to-fuel ratio," Patrick explained. This is one feature that makes the system user-friendly because you will always have the proper fuel flow at the start of a run and at the end, even if the pressure drops, or as the bottle runs low. It's also a great safety feature because the fuel flow is increased if the bottle pressure is raised.

Often, magazines tests are done on fresh race engines or dyno test mules designed for such abuse. Well, this time we decided to get down and dirty and add the nitrous kit to a well-worn 5-liter engine. One of the many frequently asked questions we get here at MM&FF Command Central is, "Can I modify my Mustang, even though it has 100,000 miles (or more) on the engine?" Now anyone who knows squat about engines will tell you it's not normally a good idea to start your project with a high mileage bullet under the hood, but the 5-liter, with its short stroke, small diameter crankshaft main journals and roller cam is quite the trooper.

In most cases, the stock short-block can take a pretty large horsepower increase if treated to regular oil changes and if detonation is avoided. To prove or disprove this theory, we asked Chris Winter of Crazy Horse Racing (South Amboy, N.J.) if we could install the ZEX kit on his daily driven 1992 GT, which has racked up a whopping 147,500 miles. Winter obliged, as he too was curious about the potential results of the kit.

Disclaimer: Before moving ahead we must inform you that Winter's engine is meticulously maintained and a good portion of the miles came from highway driving, not street bashing. I'll reinforce the fact that his car has not been beaten on, although it has been down the drag strip and around some of the best road courses in the country. And it's stock, save for a 70mm throttle body and a K&N filter.

After examining the kit and reading the instructions carefully, we got to work by disconnecting the battery. We mounted the nitrous bottle in the hatch and then we ran the line from the bottle to the engine compartment. Next, we mounted the Nitrous Management Unit and drilled, tapped and installed the nitrous injection nozzle in the throttle body. As for the wiring, there are only a few to connect. The black goes to ground, the white goes to output voltage on the TPS and the red goes to the arming switch. And after completing the wiring we finished up by programming the system, as per the manual.

This involves turning on the activation switch and then cycling the key to the "on" position. Next we depressed the push-button on the NMU and the little LED light turned red, as the instructions said it would. This informs you that the NMU is the in the "learning mode." We then depressed the throttle to the wide-open position and held it there for 10 seconds. The light then flashed from red to green to inform us that it has successfully learned the voltage curve of the vehicle's TPS. To confirm this we cycled the arming switch off and then on and the light stayed green. Lastly, we pushed the throttle to the floor to confirm that that the activation solenoid was opening and closing.

Amazingly, all this work was completed in less than three hours.

The Test
As with any aftermarket part (or parts), you'll want to know if it worked or if you've wasted your time and money. So, we got to business and strapped the workhorse '92 GT to the Dynojet for a little dyno test.

As we mentioned earlier, the engine in question is stock as a rock, with the exception of a 70mm throttle body and a K&N cone-style filter. We baselined the 302 with the timing at 14 degrees BTDC and the result was 222 horsepower at 4800 rpm and 295 lbs.-ft. of torque at 3400 rpm. Those numbers are pretty typical of a mass air-equipped 5-liter with the timing bumped and a K&N. For the first test of the ZEX we installed the 75 horsepower jet and the accompanying No. 43 fuel jet. Naturally, we had premium 93 octane fuel in the tank (ZEX literature recommends 92 octane as the minimum) and we backed the timing off to 12 degrees. Note: The ZEX reference chart states that you don't need to back off the timing with the 75 horsepower jet; however, we assume they figure that the owner is using the stock 10 degree base timing setting as a starting point.

Winter then cracked open the bottle, hopped in and let the green and silver GT rip. The engine, now being fed copious amounts of air and fuel, snapped to life and spit out 279 horsepower (at 4700 rpm) and an amazing 394 lbs.-ft. of torque at 3400 rpm. That's a gain of 57 horsepower at the wheels and 99 lbs.-ft. of torque.

The simplicity of the kit allowed us to make our next change in only a few minutes. We removed the filter to gain access to the NMU and slipped in the No. 52 nitrous jet and the No. 38 fuel jet, which in combination are the jets that make up the 125 shot. We elected to skip the 100-horsepower shot to save a little juice for the street after the testing. Winter also backed off the base timing another four degrees (to eight degrees BTDC) before making the pull. With the changes in place we made the final test and saw another gain in horsepower and torque. Horsepower climbed to a peak of 303 at 4800 rpm, though torque jumped to 430 at 3000 rpm. Total gain for the ZEX kit over stock was now 81 horsepower and 135 lbs.-ft. of torque and all for only $525. However, at 3000 rpm the ZEX kit (with the 125-hp shot) helps the 302 make 90 extra rwhp over stock (with 14 degrees of timing advance).

We were really pleased with the results of the ZEX nitrous kit. Installation was a breeze and the kit performed as advertised. We even took the GT out for a spell on the street and had a little fun with the extra power. The increase in torque made the GT really responsive in the mid-rpm range and the power stayed on past 5000 rpm. Of course we could add race gas and bump the timing up, but we decided to leave well enough alone.

In the end we proved that a well-worn 5-liter can handle a shot of juice, but you've got to be smart. If you beat the daylights out of your car it will surely return the favor and break on you. That's why we'll take it easy and reserve the beatings for the track, and hopefully our green machine will make it to 200,000 miles. Maybe then we'll up the power again.