One of the things you learn quickly about nitrous is that it will reveal any weaknesses in your engine. For example, after I installed the throttle switch, I found out the gas pedal wouldn't open up the carb far enough to engage it. Seems I'd been driving around for six months with no more than 50 percent throttle. Adjusting the cable bracket and bending the pedal assembly outwards fixed that problem--and lo and behold, it drove like a different car, even without nitrous.
Another, more insidious problem, is that of fuel pressure. In the instructions, you'll find a warning that the fuel system must have no less than 6 psi of pressure right at the nitrous solenoid. Any less runs the risk of engine damage. In order to check the pressure, I installed an inline fitting with an integral fuel-pressure gauge just ahead of the nitrous solenoid. It showed between 6 and 9 psi initially but tended to drop below 6 when the engine was hot.
In an effort to ensure that didn't happen with the spray on, I looked for ways to make sure I knew exactly what was going on under the hood. Two items quickly surfaced. The first was a warning-light kit, calibrated to come on if pressure dropped below 6 psi. To wire it in, I joined another wire to the one coming from the arming switch and ran it to one terminal of a 12-volt warning light. From there, I ran the wire off the light's other terminal to the self-grounding pressure switch, then mounted the switch in a brass tee to the gauge fitting I'd already attached to the fuel solenoid. Since both the gauge and the switch had a 1?8-inch pipe thread (NPT), they both fit easily into the tee.
While you can build your own system like this, I was unable to locate the switch anywhere but Jegs. Most pressure switches operate at a range--say, 5-12 psi--which means that each switch will function somewhere in that range, but you won't know where without buying one and testing it. The Jegs switch is pre-calibrated to 6 psi.
The second item is a safety switch. Adjustable from 5 to 24 psi, it's wired into the same circuit as the arming and throttle switches. Should fuel pressure drop, it will kill the whole nitrous system. We installed it in the same fitting as the other switch by drilling an additional 21/64-inch hole and using a 1/8-inch NPT tap to thread it. This is a $30 part, and considering that it could save your engine, only a fool would omit it.
Two other things you'll need to do prior to running "the juice" are changing the spark plugs to a set two steps colder than standard, and retarding the top-end timing to reduce the potential for detonation. The exact amount of timing retard needed varies with the power level you select, and that information is included in the jet-selection chart that comes with the instructions. For adding 100 horsepower, we needed to pull it back by 4 degrees.
With the basic installation done and everything double-checked, I pointed the car in straight line, hit the switch, and laid into it. And when the bottle hit, and the car suddenly started laying down more than 400 horses at the wheels, believe me, Scarlett was gone with the wind.
In the next installment, we'll look at making the most of the nitrous installation: fine-tuning the fuel delivery, adding a purge (for quicker response) and a safety blow-down (to make the car legal for the track), and getting some numbers to show the horsepower gains.
Special thanks to Leon Arrowood, Dave Emanuel, Tim Faircloth, and Tray Walden.