Nitrous Oxide, NOS - How To Install

Nitrous How To Install - 2003 Celica GTS
By mrtomcat (

Here are some pictures/hints of my just recently finished Nitrous Install. Since the instructions are not always too good this can be used as a reference.

Nitrous Express EFI Kit
Nitrous Express GenX II Kit
Nitrous Express TPS Switch
Nitrous Express Universal Console
Mallory D646 Window Switch
NGK BKR7ES-11 Spark Plugs

To start out make sure you read the manuals a few times and check out what other people have done. I spent quite some time at pep boys for wiring needs they have a much better selection for the electronics than fry's or home depot which surprised me.

First of all you need new spark plugs that are at least 2 points colder. Recommended are NGK Copper plucks. Their site states that iridium works well with nitrous as well but stay away from platinum. I got mine at since these are usually not stocked in stores (but you might get lucky)

I routed the main nitrous line through the rubber grommet by the spare tire and zip tied it together with the other lines going to the engine compartment and then through the engine plastics to the front. Unfortunately the line wasn't long enough so I had to buy another 3 feet line and a connector. One can also route the line through the cockpit but I didn't like that...

In order to still use the trunk for everyday use and so to protect the bottle, I built a casing that's locked to the chassis. It also makes the bottle in the car a little less obvious for people walking by.

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Here are some pictures of the Bottle. I originally had the remote opener but took it off again for the following three reasons: 1) It needs lots of power and needs to be connected to the battery directly. By the time I found out I had just finished all the wiring and didn't want to crawl under the dash again to push more wires to the engine compartment. 2) There's no way to tell when the bottle is fully or partially open or closed and since I didn't want to spend another $300 for a remote pressure gauge the only way to tell is by going to the trunk...once there you might as well open the bottle by hand. 3) It forces me to contain myself from spraying all the time.

Getting the Blow Down tube in place was a challenge. A hole had to be drilled next to the bottle (be careful my buddy accidentally drilled a bit into the frame and I had to have that fixed by a frame repair shop $50 but they drilled the hole at the right place and replaced the paint to make it look professional as well). I measured the length needed for the tube and sawed off the excess tubing (again don't cut it too short leave a bit of room in case you need to move the bottle) I got a rubber grommet so that there won't be any leaks during rainy weather.

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The bottle heater needs the relay close to it (under the carpet) I routed the wires to the cockpit through the plastics and then underneath the passenger seat.

I installed the NX Universal Controller unit (3 buttons) one button is supposed to be the arm button in one direction and the bottle heater on button in the other. The next one is the purge button and the last one is for the bottle opener. Now I have no clue why they would separate the bottle heater from the arming switch I for once want the heater on when the system is armed so I ignored that option and wired the following way: Splice into Cigarette lighter power wire and connect a grounding wire to chassis (do not splice into cigarette ground wire this causes some very strange behavior to say the least) . Connect the two to the arming switch. Now splice into the power wire going to the nitrous kit and splice in the purge and the bottle heater wires. That way you can only heat and purge when the system is armed. Make sure you connect the Heater Relay directly to the battery (with an inline fuse of course (12 gauge wire and 20 amp fuse) or it won't have enough power...I had to find out the hard way. Since I removed the remote bottle opener this button is just a place holder (update: since I had to connect the heater relay directly to the battery I also wired up the remote opener again so if I decide to use it I just need to plug it in). Next to the buttons I placed an amber light that lights when I'm actually spraying (System armed, TPS at wot, window switch open).

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The power line to the nitrous kit then goes into the TPS Switch needed on the 03 because of the Drive by Wire feature (no more throttle cable). The switch is also spliced into the cigarette lighter and grounded independently. It gets another wire from the ECU VTA terminal (black wire with white stripe) sorry I was too lazy to open the ECU box to take a picture...The VTA terminal sends a 4 volt signal when at wide open throttle which you should test with a volt meter first. Once you confirmed that's working connect it to the white wire on the TPS and calibrate according to instructions (the red light on the switch should come on when at wot) the pink cable then goes into the first orange wire of the Mallory d646 window switch. The Mallory switch is also spliced into the cigarette lighter and grounded independently. I configured the switch for 4 Cylinder (duh...) open window at 3000 rpm and close at 8000 rpm (IMPORTANT: the closing point has to be no later than 200 rpm before the limiter kicks in otherwise your engine goes bye bye fast!) My limiter kicks in at 8350 rpm so I got another 150 rpm safety window. The brown wire with white stripe from the ECU (the tach terminal) needs to be connected to the green wire. The second orange wire then gets connected to the NX kit into the engine compartment into the relay. Note: you can also plug in a horn relay in between which I did at first but didn't like nor deemed necessary. I mounted these switches with velcro.

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I added an inline fuse to the relay wire that connects directly to the battery as an additional safety precaution. From there on it went to the solenoids.

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In order to mount the solenoids I bought a few pieces from home depot and build a little frame. I drilled the required hole into the Intake (I lined it out with duct tape in order to catch the metal debris that would have otherwise ended up in the engine). I wish however I would have drilled the nozzle hole in the back of the Intake, to conceal a bit better and that the Hood wont touch the lines (I got very lucky here...make sure you are still able to close the Hood!!!). The wiring here is pretty much as the manual suggests. Including splicing into the fuel line. Fuel line into Fuel Safety switch into Fuel Solenoid into Shark Nozzle. Nitrous line into Nitrous Solenoid into Shark Nozzle and into Purge Solenoid. Ground to the frame.

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I cut the purge tube and secured a polyurethane refrigerator tube on it, routed it to the side underneath the plastics and drilled a hole next to the wiper fluid line into the plastics and routed the line outside the windshield so that is sprays up.

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After that of course make sure there are no leaks and start testing without the engine running or open bottle...

I set up a few jumpers in order to test and troubleshoot some of the steps.

Here are two more pictures of the engine bay with the completed install

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In closing:
I recommend doing this yourself if you have some basic electronics knowledge. It took me a while to do but at least I know exactly what is where and how it works and I have only myself to blame if something goes wrong. It's also a lot of fun and I learned a lot. I also want to thank some of the newcelica members that were very helpful when I got stuck or just simply needed confirmation on an issue.

Source: newcelica