Understanding Nitrous And How To Use It In Bracket Racing

It’s generally acknowledged that, dollar-for-dollar, the best investment in performance enhancement is a nitrous oxide system. Basic kits for both carbureted and electronically fuel-injected engines are available for under $400. More sophisticated setups are available that can add 500-plus horsepower to an engine that’s built to handle the increase. But how does any of this translate to bracket racing success?

For input on the subject, we turned to none other than Mike Thermos, who founded NOS back in the late 1970s, sold it to Holley in 2000, and has operated a new firm, Nitrous Supply, since 2004. Known as the “Godfather of Pro Mod,” he brings more than 45 years of nitrous experience to the table. Also contributing to this article is Steve Brulé, Westech Performance Group’s dyno tuner extraordinaire and co-host of the highly informative “Engine Masters” show on MotorTrend TV.

Nitrous 101

According to Thermos, “Nitrous oxide is kind of a ‘cheap date’ as you can get a lot of performance from a minimal investment. Think of a 150-shot of nitrous as providing the benefits of adding 100 cubic inches of displacement to the engine. And picking up a few seconds in elapsed time is fun, to be sure.” There can also be monetary advantages in advancing to a quicker bracket at some tracks.

A basic plate kit for 4-barrel carbs is popular with e.t. bracket racers. They can provide up to 175 extra horsepower and are available for under $400. EFI kits are also available.

Winning in bracket racing, of course, boils down to consistency. And the key to success with nitrous — or any normally aspirated or power-adder motor for that matter— is vigilant tuning. To be sure, there are many bracket racers who win with nitrous.

Nitrous oxide enhances performance in two ways; it cools the air/fuel mixture by some 60 degrees, which contributes to increased combustion efficiency, plus — more importantly — the oxygen molecules released from the nitrous (along with added fuel) provide even more power. After conducting numerous analyses Brulé says, “A good rule of thumb is that for every 10 degrees you cool the air/fuel mixture temperature, it increases power by about 1 percent. However, the air inlet temperature will vary depending on the amount of nitrous.”

Can you get too much of a good thing? According to Brulé, “We’ve found that using a nitrous system that adds approximately 40 percent to an engine’s normally aspirated output won’t affect reliability in any way. It’s a safe goal. So, a 250-shot of nitrous is perfect for an engine with just over 600 horsepower. By comparison, a relatively mild 350 cubic-inch small-block that puts out about 1.25 horsepower per cubic inch is a prime candidate for a 150-shot system.” Steve added, “We’ve done experiments where we just keep feeding more and more nitrous to an engine to see where it goes and the limit is about 70 percent of naturally aspirated output before the engine blows up.”

More than just a show, purging the nitrous line prior to a run removes any trapped air and ensures getting a full charge of nitrous at the hit.

There are four important factors to contend with in tuning a nitrous-boosted engine. They include bottle pressure, bottle temperature, the amount of nitrous in the bottle, and jetting — the latter being a factor in optimizing the fuel side of the equation, too.

We’ve found that using a nitrous system that adds approximately 40 percent to an engine’s normally aspirated output won’t affect reliability in any way. – Steve Brulé, Westech Performance

Bottle pressure should be maintained at or above 900 psi — anything less will affect the volume of the discharge. At a certain point, the reduced amount of nitrous oxide left in the bottle will cause a pressure drop. Topping off the bottle after a few runs will assure consistent pressure. Maintaining consistent line pressure is also important, and purging the system can eliminate any air pockets and also bleed off any excess pressure.

Temperature also has a bearing on pressure and can be used to maintain consistent pressure with a reduced volume of nitrous in the bottle, according to Brulé.


“In our dyno testing, we’ve found that 92 degrees Fahrenheit provides the most consistent results, with pressure falling within a 950 to 1,050 psi range.” If the ambient temperature is colder than the optimum bottle temperature, you can use an electric blanket-type heater (most work on both 110V and 12V) to maintain the desired temperature, or immerse it in warm water. Never use a torch or other concentrated heat element to warm the bottle; the heat must be applied evenly. There are documented cases of nitrous bottles blowing up when heated with a torch.

It should be noted that pressure and temperature will fluctuate in the real world, and that a full bottle will require less temperature to achieve the same pressure as a less-full bottle, and ultimately, pressure is the critical parameter to regulate.

Solenoids play an important role in any nitrous oxide system, with both fuel and nitrous flow influenced by the orifice size and activation speed. Nitrous solenoids are available ranging from 0.078” to 0.250”.

Maintaining consistent fuel pressure is also important, with accurate regulation a key component of the fuel system.  And on those race cars without a battery charging system (alternator), it’s important to maintain the charge, as a neglected battery can lose power and affect fuel pressure, solenoid responses, and other functions. Employing an electrical “systems check” is recommended.

Monitoring the engine tune can be accomplished by the tried-and-true method of “reading” spark plugs — with the presence of nitrous not affecting normal procedures. As an aside, colder heat range plugs are recommended for use with nitrous. Likewise, the ignition should be retarded.

“On Westech’s dyno, we primarily rely on the air/fuel ratio for tuning,” says Brulé, who added, “today there are also many affordable in-car Lambda air/fuel ratio monitors that should be considered by any serious bracket racer.”

Bringing Nitrous Into Your Bracket Racing Program

Since the majority of bracket racers run V8 engines with a four-barrel carburetor, plate-type nitrous systems are the most popular. These range from twin-bar (one for nitrous, one for fuel) setups to special 4-bar “criss-cross” and perimeter designs. According to Brulé, there’s a popular misconception that you need a single-plane intake manifold in order for the nitrous to be effective. “Our tests have shown basic plate-type systems to work well with dual-plane manifolds.” Brulé” adds, “When you’re after serious power gains with nitrous, you’ll want to use a fogger-type system with a single-plane manifold so you can individually tune each cylinder.”

The type of plate can influence power. The criss-cross design with two nitrous bars and two fuel bars serves to provide a more potent mixture.

Thermos added, “The manner in which the nitrous and fuel are introduced into the manifold is important. Fogger nozzles should be positioned so the mixture is disbursed to take advantage of the intake runner flow path. You need to ‘aim’ the shot. We have recently developed a new nozzle called the ‘Fang II’ that essentially envelopes the nitrous in fuel and delivers a blended charge into the engine.”

There is obviously a myriad of factors involved with registering consistent performances over and above the nitrous system. Track temperature, density altitude, tire condition/pressure, and suspension setup are but some of the variables. At the heart of this is diligent note-taking with the possible use of data-logging equipment.

Bottle valves play an important role in the quest for horsepower. The NS “Outlaw Power Valve” (right) has a big 1/2-inch orifice, uses a 5/8-inch siphon tube, and has many safety features.

A key factor in consistency is the amount of nitrous in the bottle, especially if you’re racing a 1/4-mile. Thermos says, “We’ve seen racers pick up 3-4 mph in trap speed when switching to a full bottle. Having a larger 15- or 20-pound bottle instead of a 10-pound bottle can be advantageous.” Mike added, “Some racers advocate employing a NANO (nitrogen-assisted nitrous oxide) ‘push’ system, but they are complex and can often lead to complications, due to their high pressure. It’s easier to just use a larger bottle.”

The manner in which the nitrous and fuel are introduced into the manifold is important. – Mike Thermos, Nitrous Supply

Another consideration is when the nitrous is to be deployed. Race cars with sophisticated suspensions and tires to match are capable of absorbing extra power at launch. On the flip side of the coin, it’s possible to overpower the track when traction is insufficient, so the nitrous must be added systematically. This can be accomplished manually, through the use of a basic pre-set timing device (like a Digi-Set), or by employing sophisticated ECUs with nitrous controlling functions.

In summation, a nitrous oxide system can give you a huge boost in performance for a very reasonable investment; there’s nothing else on the market that has a better horsepower-per-dollar factor than nitrous. With diligent attention to detail and tuning, cars equipped with nitrous can be very consistent lap after lap. And as long as the engine has been built with quality parts, and the system is properly set up, nitrous does not adversely affect long-term reliability. It merits serious consideration…especially for racers looking to improve performance and get more fun per run.

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About the author

Bill Holland

Bill Holland has been involved in racing and the performance aftermarket since the 1960s in the capacities of racer, speed shop proprietor, journalist, street rodder, designer and advertising/PR/marketing professional. Along the way he’s raced Top Fuel and Funny Car, been editor of NHRA’s publication, National Dragster, was involved in off-roading as publisher of SCORE News, built a variety of Featured Vehicles for the SEMA Show, as well as a Track “T” that was a Contender for the AMBR award. He currently races vintage sports cars. Bill was inducted into NHRA’s California Hot Rod Reunion Hall of Fame in 2017.
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