In 2006 Jeep introduced the new Jeep Grand Cherokee. They also came out with the Street and Race Technology performance package to make the most powerful Jeep ever. The SRT-8 package includes the 6.1 liter Hemi putting out 415 horsepower and 410 lb.-ft. of torque. All that power coupled to the all wheel drive system in the Jeep turns into an SUV quicker then a Porsche Cayenne Turbo.

The Jeep can make it 0-60 in under 5 seconds, 0-100-0 in the low 19 second range and 0-60 braking in under 125 feet. The excellent braking numbers come from four-piston performance brake calipers developed by Brembo at all four wheels, finished in gloss black. Under braking, these calipers clamp down on 360 x 32mm vented rotors up front, with 350 x 28mm vented rotors in the rear.

In the Need for More Power – Preparing for Nitrous

We decided the performance was not good enough stock, so a B. Woody cold air intake had been added. In preparation for adding a Nitrous Express nitrous kit NGK 2315 Iridium plugs (2 heat ranges colder) were used. ADiablosport tuner was purchased to help with the tune. Hemi fuel curves are known to be very rich from the factory. The timing curve on the factory tune needed adjustment was it was going to be too aggressive for the 100 shot.

The Jeeps are also known for running warm, so a switch was added to turn the electric fan on and a cooler thermostat was used to keep the temperature down. We are limiting the power output to 100 hp that is run through a progressive controller. After some research we found that it is highly recommended to use higher octane fuel with anything more then 100 hp. Andy at Modern Horsepower provided a custom CMR tune for the Diablo.

What Comes in the Kit

• Fuel and Nitrous Solenoid
• 10 pound bottle with gauge
• Bottle brackets
• Fuel Line Adaptor for return
• TPS Trigger switch for Drive-By-Wire vehicles
• Fuel and Nitrous Lines for Solenoids
• Trunk to Engine bay nitrous line
• Nitrous/Fuel Nozzle
• Relay, switches, jets, connectors

Starting the NX Installation – Mounting the Bottle

Instead of drilling holes in the factory package trey, we made a new one. We cut a piece of plywood in the same shape and used a router to notch the areas for the stock latches to hold it down. Then we covered in some grey carpet similar to the factory carpet. The bottle was installed with the valve pointed towards the front of the car.

Here is the factory package trey.

Here is the custom made replacement with the bottle installed.

Running the Nitrous Line

Once the bottle and the solenoids were mounted the nitrous feed line was ran. There was a grommet in the firewall that we enlarged the opening for the line and other wires to run through later. Once the line was through the firewall we slide it behind the kick panel. From there we were able to run it under the door sill plates. The only place the line shows is right next to the rear seat, but it is not noticeable unless you are looking for it.

Installing the Solenoids

Next the fuel and nitrous solenoids were mounted to one of the t-bolt clamps on the cold air intake. The relay was mounted on the inner fender where the factory air box was formerly located. We also had a fuel pressure safety switch that was lying around that we decided to install as an additional safety measure. Solenoids are switch polarity, as long as you have one going to the switched power side of the relay and the other side ground, it does not matter which wire you choose. Both power side wires for the solenoids are tied together. You can also do this for your ground. The fuel pressure safety switch is installed on the ground side of the relay. Run the ground to the safety switch and the other side of the switch to your chassis ground. This way if a fuel pressure drop is detected, the switch will not allow the nitrous kit to ground properly, disabling the system. Though this wiring setup is for the factory TPS activation, the wiring the for nitrous controller will vary slightly, and which we will cover next.

Installing the Nitrous Controller

We already had an FJO nitrous controller lying around so we used that in place of the TPS unit that comes with the Nitrous Express kit. Nitrous Express also sells a fantastic nitrous controller that could be used. A controller is highly recommended to extend the life of the transmission. You will need access to the controller to set the TPS switch, see the flashing lights and connect to the USB port. Keep those in mind when you mount your controller. With the nitrous controller you can set what triggers the nitrous to come on and we used 2500 rpm and full throttle. You can set the percentage of nitrous that comes on at the trigger point. It was also set up to require full throttle before activation. A fuel pressure switch was added and wired into the controller. It will turn the nitrous off in case the fuel pressure drops. Thirty five percent was what we picked to start with for the hit at 2500 rpm. We set the ramp to 100 percent at 3800 rpm. All of the settings are very conservative to start out with. That will lets us creep up on the proper tune up. The 100 hp nitrous is activated at 2500 rpm with 35 percent or 35 hp and is ramped in to 100 percent at 3800 rpm. This is great for keeping the Jeep hooked up to the track and reduces the shock to the driveline.

Wiring Continued

The grounds for both solenoids are run to the controller. The power wire for the solenoids is run to the number 87 post on the relay. The number 30 post on the relay is wire run over to the fuse box. The number 85 post is run to the fuel pressure safety switch. The other side of the safety switch is run to a ground. After the solenoids and the toggle switch are connected to the nitrous controller you need to wire up the ground. It was placed with a factory ground inside the fender close to the controller. The first input on the controller was connected to the TPS wire. We used the piggy back wiring connectors provided with the NX kit to attach it to the brown with white stripe wire on the TPS. It was posted on the jeep message boards that you want to connect the controller input close to the throttle body. There is a lot that happens between the gas pedal and throttle body. The RPM wire from the controller will attach to the yellow with a black stripe wire on the number one cylinder coil pack. It is attached with the same connector as the TPS wire that is provided with the kit. After the wiring was complete we taped it up and used conduit to make it appear as factory as possible.

The activation toggle switch was mounted in a storage pocket to the left of the steering wheel. The pocket popped out so we could drill a hole and mount the toggle switch. You have to double check the clearance behind the switch, because it is close. This location is out of plain sight but easy to reach. The power for the switch was run through the firewall and to the fuse box. The ground was connected to a factory ground under the dash. The third post was tied to the nitrous controller and the number 86 post on the relay.

Installing the Fuel Line Adapter

The next step we performed was installing the fuel feed line and adapter. NX provides an adapter the fits on the return side of the fuel system. Use a fuel line tool, which is the same as the ones used on Ford vehicles, to remove the return line. The return line points straight up on the passenger side of the intake. Before installing the adapter we installed the fuel pressure safety switch on one side and the fuel feed line on the opposite side. The fuel pressure safety switch does not come with the kit but I would recommend installing it. We also added a pressure gauge to the bottle so we know the pressure.

Installing the Nozzle

We removed the cold air intake to install the nozzle that comes with the system. We drilled a 9/16” hole on the back side and in the middle of the intake tube. A file was used to clean up the edges before we put the nozzle fitting in place. A small bead of silicone sealant was placed on each side of the fitting prior to installation to keep the inlet sealed. Once the air intake is reinstalled and the solenoids are remounted you can finish the plumbing. Do NOT use Teflon on the solenoids. Nitrous Express provides a thread sealant with the kit. The Teflon can come off and get stuck in the solenoids causing problems. On the AN side of the fittings you never install sealant. The AN fitting is self sealing. Now you can run the braided lines from the solenoids to the nozzle. The lines and fittings are color coded to reduce confusion. Blue coatings are for the nitrous side and red coatings are for the fuel side.

Finishing up the Installation

Once you have everything hooked up you have to make sure the TPS signal is being picked up correctly. You have to press the set switch then go and drive the vehicle making a couple of full throttle hits. When you come back and check it there should be no lights on. If you go full throttle you can see the green light flash on. If that is the case it should be working correctly.

Now we are all hooked up and ready to play, we bust out the laptop to put the setting in the nitrous controller. Not only can you adjust when it turns on and off you can adjust the progressive rate also. We started with very conservative setting for our 100 hp shot. The nitrous turns on at 2500 rpm and turns off at 5200. We were unsure where the shift points were with the Jeep so we went conservative. The transmission will last much longer if it is not changing gears with the nitrous activated. The progressive was set to kick in at 35% which would be 35 hp and was ramped in to be 100% or 100 hp at 3800 rpm.

Off to the track we went to get a base line. We picked one of the worst weather days to head to the track for some testing. It was 100 plus degrees out and the sun was on the track all day. The word on the D.A. was in the 4500 to 5500 range but the humidity was not terrible at 20%. The thought never crossed our mind that we would need to have a helmet. The first hit was on the motor and the Jeep left off idle and ran a 13.54 at just under 104 mph. This number is not as good as most posted but it was the first time down the strip in the Jeep. The air was horrible, so it was not that disappointing. The track manager from Kansas International Raceway came running over after the pass saying we needed a helmet. Luckily they were nice enough to loan us an extra one they had laying around. After a 30 minute cool down a nitrous pass was made. The Jeep went 12.49 at 111.5 mph, which we were very happy with. With the very conservative setting in the controller we still picked up over a second with just the 100 hp jets in the Nitrous Express kit.

I feel with a little more experience launching the Jeep, some nice cool fall air and more aggressive settings in the controller it is possible to get an 11.99 out of the Jeep. All around we were impressed with the times we posted and doing it safely was a plus.

I will post an update when we make it back to the track with the new settings. We moved the shut off RPM limit from 5200 to 6000 rpm and changed the starting percentage from 35 % to 50% with the same ramp rate. Here is a photo taken by the KID photographer.