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We serve the VW parts and VW Tech needs of owners of aircooled VW Beetle, Volkswagen Bus, Karmann Ghia, Type 181 Thing, VW Type 3 Squareback / Fastback / Squareback, and Type 4 VW. Tech Tips, project advice, and quality parts for VW Restoration, VW Performance and Custom Aircooled VW projects.

Running Nitrous Oxide in a VW

Nitrous oxide can be used in your VW engine to create more horsepower. All engines operate under the same principles: better breathing, plus more fuel in a denser vapor equals more power. Using nitrous is not a whole lot different from using a bigger carburetor, a better manifold, a supercharger, or a turbocharger — all are methods to increase the amount of oxygen available for combustion. The air you and your engine breathe is made up, at sea level, of 78% gaseous nitrogen, 21% gaseous oxygen, and just 1% other gases. Nitrous oxide (N2O) is a liquid created by chemically bonding 2 molecules of nitrogen and 1 molecule of oxygen. When the nitrous oxide goes into your engine, the heat of combustion breaks the chemical bond which releases the oxygen and makes it available in a relatively high gaseous concentration compared to the concentration found in normal air, and this allows you to burn more fuel in a given time period.

Making Engine Horsepower

Engines operate by burning fuel (a process which requires the presence of Oxygen). The combustion produces gas by-products in a confined space (the cylinder). The expanded gaseous by-products push the pistons down. The force over time with which the piston is pushed down is horsepower. So if you want to make more HP, you need to burn MORE fuel, producing MORE expanded gas by-products in the same amount of space and time, and your pistons will be pushed down with MORE force. The theory is straightforward, but putting it into practice can have it’s share of obstacles! There are numerous factors that make increasing power a complex engineering problem. Below I discuss the three basic factors to consider in your quest for horsepower.

Factor 1: Engine Breathing
All fuels require oxygen in order to burn. If you want to burn more fuel, you will need to provide more oxygen. Virtually all engine performance products increase power by increasing the flow of fuel and oxygen. Camshafts, larger carburetors or valves, porting, intake manifolds, headers, superchargers, turbochargers, and nitrous oxide are clear examples of how improved engine breathing (putting in more oxygen in order to burn more fuel) will give you an increase in horsepower. Nitrous Oxide Injection is one of the most efficient ways to increase the flow of oxygen and fuel, and that is why nitrous systems produce such large horsepower increases.

Nitrous oxide itself is not a fuel! Nitrous oxide is a convenient way to add the additional oxygen required to burn more fuel in the same amount of time. The power that is created from combustion always comes from the fuel source. If you add only nitrous oxide and do not add additional fuel, you would just speed up the rate at which your engine is burning the fuel that it normally uses, and you will have and engine with holes in the pistons real fast! Nitrous oxide simply provides the oxygen you need to burn a greater quantity of fuel in the same time period; the overall effect is a tremendous increase in the total amount of energy, or power, released from the fuel and available for accelerating your vehicle. Nitrous oxide is a tool for manipulating an increase to the amount of oxygen that will be present when you add additional fuel in an attempt to release more power.

Factor 2: Fuel Availability
Another basic power factor is vaporization of the fuel. Racing fuels, including gasoline, will not burn in a liquid state. Gasoline must be turned into a vapor for it to be available to burn. This mechanism for turning liquid gasoline into a vapor is simple evaporation — no different from setting a glass of water outside and waiting for it to dry up. However, in the engine, vaporization happens very quickly. Engine heat and fuel atomization are the keys to accelerating the evaporation process enough to turn raw gasoline into a vapor at 8000 RPM. The process of atomization turns raw fuel flow into tiny droplets which then evaporate faster due to the larger amount of surface area made available. The size of the fuel droplets is very important. Take a large droplet of gasoline, break it up into 10 smaller droplets, and you’ve increased the surface area for more efficient evaporation. The result is more fuel available to be burned and do work during combustion. A well-designed nitrous system will produce very small droplet sizes in the supplemental fuel that flows into the engine with nitrous. This is one of the reasons that the NOS FOGGER Nozzles make more horsepower than some other systems.

Factor 3: Air / Fuel Mixture Density
The third basic power factor we will look at is air/fuel mixture density. Ever try to jog on top of a 10,000 foot pass in the Rockies? Leaves you gasping for breath, doesn’t it? That’s because the air is thinner (less dense, or less air in the air, so to speak) when you are higher up in the atmosphere than it is at sea level. Air density is affected by atmospheric pressure (the weight of the atmosphere above you), heat, and humidity. Within an engine, we can’t change the pressure of the atmosphere; but we can regulate the heat of our intake charge to some extent. Intercoolers make extra power by cooling the fuel and air/fuel mixture to make it more dense. And the denser the mixture is, the more the cylinder is packed with fuel and air to burn and make power. When nitrous oxide is injected, it turns from a liquid to a VERY COLD vapor, and this cold nitrous vapor drops the temperature of the whole intake charge in the manifold by as much as 65 degrees F! The denser mixture that results helps an engine produce even more extra horsepower with a nitrous system, than without one.

Types of Nitrous Oxide Systems
There are three basic types of nitrous systems: dry, wet, and direct port.

Dry Nitrous Oxide System
The “dry” type of nitrous system is the least well understood. A “dry” nitrous system simply injects pure Nitrous, but does not address the fact that you have to have some means to add the additional fuel to leverage the extra oxygen. The “Dry” shot keeps the upper intake dry of fuel, and is best used on FI engines. You can add additional fuel by either increasing the pressure to the injectors by applying nitrous pressure from the solenoid assembly when the system is activated, which causes an increase in fuel flow just like turning up the pressure on your garden hose from 1/2 to full. The second way we can add the required fuel is to increase the time the fuel injector stays on. This is accomplished by changing what the computer sees, basically tricking the computer into adding the required fuel. In either case, once the fuel has been added, the nitrous can be introduced to burn the supplemental fuel and generate additional power.

Wet Nitrous System
The second type of nitrous kit is the “wet” style of kit, which is the one most commonly implemented on aircooled VW engines. These kits add nitrous and fuel at the same time. This type of system will make the upper intake wet with fuel, and are best used with intakes designed for wet flow and turbo/supercharged applications. The reason for this is the fact that fuel flows differently than air or nitrous. This difference in flow characteristics can lead to distribution problems and, in some cases, intake backfires (BOOM!)

Intakes designed for wet flow (such as with carburetors) cause much less separation of the nitrous/air, and fuel. Modern fuel injection intakes are designed to flow only air (they have tighter turns and a more compact design as a result), and generally do not make good candidates for wet flow nitrous systems.

Direct Port Nitrous System
The last type of system is the direct port system, which is what we use on the Flat-4 VW Aircooled Engine. Just as it’s name implies, it introduces the nitrous and fuel directly into each intake port on an engine. These systems will normally add the nitrous and fuel together through a fogger nozzle. The fogger nozzle mixes and meters the nitrous and fuel delivered to each cylinder. This is the most powerful and one of the most accurate type of systems, due to the placement of the nozzle in each runner, as well as the ability to use more and higher capacity solenoid valves. A direct port system will have a distribution block and solenoid assembly which delivers the nitrous and fuel to the nozzles by way of connecting tubes. Because each cylinder has a specific nozzle and jetting (both nitrous and fuel), it is possible to control the nitrous/fuel ratio for one cylinder without changing that of the other cylinders. These systems are also one of the more complicated systems when installation is considered, since the intake must be drilled, tapped, and the “plumbing” made to clear any existing obstructions. Because of this and the high output of these systems, they are most often used on racing vehicles built for the strain of such high horsepower levels.

Tips for Running Nitrous in a VW

1- The kit is only the beginning of doing a NOS motor. You will spend as much if not more money on the extras as the initial kit. DO NOT SKIMP ON ANYTHING! You will pay one way or another.

2- The things you must have that aren’t in the kit are: quality NOS filter, quality gas filter, purge system, Hobbs safety switch for fuel and some form of triggering the system.

3- As for triggering the system, a throttle switch is best, because (1) It will be consistent at the track. I.E. as long as your foot is on the floor you got NAAAWWWSSSSS! (2) In case of trouble your first instinct is to get out of the gas. No thinking involved about leaving go of a button.

4- The timing shouldn’t advance more than 28 degrees total when on the juice; This means running some form of timing retard system triggered off the NOS switch. The nice Mallory has this built in.

5- The rule of thumb of the same size fuel and NOS jets the same size throughout only applies to a fuel injected car! If running carbs the rule of thumb is a two size difference in favor of the fuel. For instance, a #18 NOS jet and #20 fuel will get you approximately 50hp. This all depends on fuel pressure and bottle pressure.

6-You MUST have to have two separate fuel systems. If you do use the same pump you will need separate pressure regulators. The NOS fuel pressure will need to be 6psi minimum. This needs to be checked with all lines and jets connected for it to be correct.

7- Bottle pressure is very critical. The operating psi is between 900 and 1200 lbs. In hot climates and weather it is so hot all the time you won’t need a “bottle blanket”. Instead, you may have to use a towel that is soaked in a cooler to keep the pressure from getting too high. A quality NOS pressure gauge is a must.

8- Solenoids won’t last forever! They need to be rebuilt about every 100lbs of NOS that goes through them. This cost about $40 a rebuild. If you are serious, keep a spare NOS and fuel solenoid on hand. You can also use quick connectors so they can be changed fairly fast. DO NOT leave the bottle pressure valve open when the system isn’t in use. Close the bottle and purge the system on the return road after every run. If you leave the bottle open between rounds the solenoids will last a very short time; don’t find this out the hard way $$$$.

9- Remember, even with every safety gadget known to man, there are no guarantees. Bad things can and DO happen.

10-GO HAVE FUN! If you can stomach all of the above, time to laugh a little. Most people think it is easy to do a NOS setup. When you don’t take the time and energy to do it right it WILL bite you in the butt and eat your wallet. Now you can see why not many people run NOS SUCCESSFULLY. We really hope this will help you.

Special thanks to LoCash John for these tips on running Nitrous Oxide.
Aircooled.Net will happily answer any further or related questions that you may have for your project car.