Nitrous is the great equalizer. Used properly, it can transform a mediocre street runner into a giant killer. It's not unusual to see what appears to be a simple 200hp plate to actually be pushing closer to 500 hp. Then there are the fogger systems that can make even more. Induction Solutions (Induction Solutions.com) posted a short video on its home page showing an 18-degree SBC intake manifold “levitating” off the bench with a 600hp shot shooting out of the fogger nozzles. With these big horsepower numbers also comes major tuning responsibility: you'd best have your all ducks beak-to-tail if you're going to play with nitrous. More importantly, the basics of nitrous tuning remain the same for all systems, no matter how much or how little nitrous you push through an engine. Not surprisingly, it's many of these same basics that are often overlooked or ignored in the rush to go fast. If you're lucky, the cost of this ignorance is merely unrealized horsepower. But this same inattention can just as easily escalate into more costly mistakes.
Nitrous is expensive and, like you, we want to get the most horsepower bang for our N2O buck. So went looking for the tricks that the smart nitrous tuners know all too well. It turns out that a properly tuned nitrous system has less to do with magic and more about acknowledging all the little details that make each nitrous pass more consistent. Let's dig into those details and see if there are a few you may have overlooked.
If there is one overriding factor that affects fast gas tuning, it has to be nitrous pressure. We see it all the time with part-time racers and street runners who want to go fast but may not understand the basics about pressurized gases. We'll start with the nitrous in the bottle. A full bottle at room temperature (72 degrees F) will be at 760 psi, and most of the nitrous oxide will be in a liquid state. Below this pressure, nitrous will begin to phase change from a liquid to a gas, which is less dense. The object is to inject liquid nitrous at the discharge nozzle to maximize the benefit of both the nitrous and its cooling effect. You may be aware that nitrous exits a nozzle (or anywhere there's a leak) at roughly –120 degrees. That's why it so easily burns bare skin when released under pressure. Conversely, if we warm the bottle using hot water or a heat blanket (never, ever an open flame), pressure in the bottle will increase. But the critical pressure/temperature window is rather narrow. If the bottle reaches a temperature in excess of 98 to 100 degrees, the nitrous begins the process of changing back from a liquid into a gas. This means the ideal nitrous pressure is midpoint within this ideal pressure/temperature range—between 84 and 88 degrees, which is equivalent to 900 to 950 psi. This means that on hot days, you will have to cool the bottle with ice or wet towels, while you will have to warm the bottle to maintain this optimal pressure on cool race nights.
According to long-time nitrous tuner Steve Johnson, owner of Induction Solutions, it's better to be a little on the low/cool side of the pressure/temperature curve than on the hot side. It's not uncommon to see nitrous bottles with temperatures barely at 70 degrees (670 psi), which is too low and will deliver less than optimal power. Conversely, jacking nitrous pressure up over 1,050 psi degrades nitrous performance because some of the liquid nitrous will revert back to a gas—not what you want. A fairly common summertime affliction is when bottle pressure spikes because of excess heat. The first indication of this excess pressure will be when the nitrous solenoid won't open when triggered. Steve says that pressure in excess of 1,000 psi is the leading cause of damage to the nitrous solenoid seal, and a leaking nitrous solenoid is the most common cause of nitrous backfires. If you've ever witnessed one of these explosions, we don't need to tell you how badly it mangles the carburetor and sometimes even the intake manifold. There's a good reason companies sell nitrous burst plates to help vent the violence. Don't be the guy who launches a 10-foot flame out of his carburetor.
Making more horsepower is as easy as swapping nitrous jets and hitting the button. Tune it right, and there's plenty of power available.
Nitrous bottle weight is a critical variable. A properly filled bottle will retain roughly 50 percent of area for the gas above the same level of liquid nitrous. This “head room” creates less of a pressure drop when the nitrous is used. An overfilled bottle means there's less area above the liquid nitrous. The area above the liquid nitrous on an overfilled bottle increases dramatically, causing a greater than normal pressure drop during the initial use. This NOS bottle lists bottle weight at 14 pounds, 10 ounces; with 10 pounds of nitrous, the bottle should weigh 24 pounds, 10 ounces.
We put an Induction Solutions quarter-turn ball valve and 4-inch, liquid-filled, nitrous-pressure gauge in the cockpit of our Orange Peel Chevelle. This way we can accurately monitor nitrous bottle pressure and increase the nitrous solenoid seal life by isolating bottle pressure from the solenoid until right before use. Steve Johnson says that long-term exposure of the nitrous solenoid seal to bottle pressure will quickly degrade the seal.