Nitrous is the easiest, cheapest, and fastest way to make more horsepower. Like anything else that seems to be too good to be true, mention it and you’ll be swarmed by warnings of engine doom. Yet, amid all those loud warnings, there are plenty of performance nuts who run it with no problem and urge you to dive in headfirst. So…who's right?
Both schools of thought are correct. Nitrous can be brutal on engines, wreaking havoc if mishandled. However, with some thoughtful supporting mods (and the right precautions), you can tap into its instant power gains and join the rest of the nitrous-loving world.
What are the mods you need to make? Well, that ultimately depends on how much nitrous you're throwing at an engine -- and what you're starting with. We'll give you the crash course you need to get things rolling.
How Does Nitrous Work Exactly?
At the heart of a nitrous system lies the nitrous oxide bottle. It captures the imagination, leaving many to believe it contains some potent, explosive concoction. In truth, all it really does is introduce more oxygen into the combustion chamber to help burn more fuel to make more power.
Yep, good old oxygen is the secret ingredient.
Nitrous oxide is non-flammable in its liquid state, which is how it exists in the bottle. However, it turns into a gaseous form during injection. When subjected to the combustion cycle, it separates, leaving your engine with an abundance of oxygen to make more power with.
The primary risks of nitrous directly relate to how it works. The sudden increase in power places immense stress on vehicle components, and can easily lead to catastrophic failure if the engine isn’t built to properly handle the strain.
Additionally, the sudden increase of oxygen can cause the air-fuel mixture to ignite prematurely in a combustion event known as detonation (sometimes called knock or pre-ignition). This scenario is what most people think about when they argue the dangers of nitrous—and rightfully so, as detonation is an engine killer no matter how well-built the bottom end is. Both the timing and fuel curve must be adjusted to add enough fuel and retard the timing so the engine doesn't blow.
Nitrous On Stock Engines?
We've all seen people throw nitrous at even the most basic engines with stock internals, and to much success. They often achieve this with minimal mods too, doing little more than some basic plumbing and wiring to hook the bottle up. So, why isn't it risky for them?
Nitrous injection systems are designed to help an engine build a certain amount of additional power. How much power depends on the kit, with most being available in shot sizes from 50-250 hp.
Most of the time, when you see nitrous tossed on a stock engine, it's a smaller kit. Something in the 50-75 hp range is generally used in these instances. (Unless they're outright trying to see how much nitrous an engine can take before it blows.) Anything more than that and serious modifications must be made for the engine to survive. However, even with the smaller shot, some changes must be made to avoid harming your engine.
Necessary Changes to Support Nitrous
With all of that out of the way, let's finally get into what you need to do to your engine for it to safely run on nitrous. Please remember that everything discussed here is a general guideline.
When and how you make changes to your engine depends on the specifics of your application and how much nitrous you are trying to run. However, the points below will always be addressed when making this upgrade.
Engine Health. An old, worn engine is more likely to experience failure when nitrous is introduced. Making sure everything is in good health is essential to avoiding catastrophic failure. At the very least, run a compression check to ensure the engine is to spec before adding nitrous.
Spark Plugs. The factory or current spark plugs in your engine are likely to be too hot to safely run nitrous. You will need to move to a cooler heat range, even with a 50-hp kit. How much cooler depends on the specifics of your application, but one heat-range lower than what you previously ran is a good starting point for smaller kits.
Ignition Timing. Ignition timing will need to be retarded whenever nitrous is introduced. The general rule is taking two degrees of timing out of an engine for every 50 horsepower that the nitrous produces. This rule applies to the stock timing, not what an aftermarket tune changes it to.
Fuel. More oxygen means you can burn more fuel—not that the existing fuel will burn any better. It's important that you maintain an optimal fuel-to-air ratio to make good power and to avoid going lean and blowing your engine. In the case of nitrous, that means introducing more fuel to the engine. Effective upgrades are highly dependent on the application and the amount of nitrous you're running. Carbureted applications need bigger jets; EFI systems need a tune, then bigger injectors. And you can bet on a bigger fuel pump being necessary for high-horsepower hits.
Fuel Octane. Again, detonation is the enemy here—and a surefire way to suffer it is by running fuel with too low of an octane rating. What octane rating is necessary depends on what the car needs in stock form, but you can always count on having to bump up a few points, even with the smallest shot of nitrous.
What About Forged Internals and Ring Gap?
As you get into higher horsepower nitrous kits, an engine will need to undergo some serious modifications to handle the extreme increase in power. Generally speaking, anything 100-hp and up will warrant reinforcing your bottom end.
In almost all cases, you'll need to upgrade to high-quality forged internals. Pistons, rods, and the crankshaft may all need to be addressed. However, there's more to consider than just “beefier” parts. The ring gap on the pistons will need to be set according to the amount of nitrous you intend to run.
Another general rule – general being the key word – is that you will need to formulate your ring gap by multiplying your bore in inches by .005. (For reference, the formula for naturally-aspirated engines is multiplying the bore by .004.) The increased ring gap is necessary to accommodate the increased expansion of the rings on account of the higher heat created when nitrous is introduced. Skipping this step will result in catastrophic engine failure.
So, What Nitrous Kit Should I Pick?
There are a lot of different types of nitrous kits available. You will need to pick which is best for you based on your particular demands, and that's a whole process in itself. However, if you're after the easy, simple, bolt-on kits everyone raves about, you'll want to select either a wet or dry system.
The basic difference between the two is that a wet system mixes the nitrous oxide with fuel prior to introducing it to the engine. This greatly reduces the risk of detonation, but does make installation more complicated.
Dry systems, by comparison, are simple to set up but don't offer that extra layer of defense against engine failure. Deciding which to go with ultimately comes down to the specifics of what you're working with and how easily you can accommodate the increased oxygen in the engine on its own.