Jet Science-What You Need to Know About Jets

by Mark Wennin
Jet Science-What You Need to Know About Jets

With all of the components a nitrous system may consist of, the jet is one of the most overlooked parts that can cause performance issues. In this article, we'll dive into what a jet does, differences between jets, proper jet selection, and problems jets can cause.


What a Jet Does

What is a jet? It is a rather small piece that performs a very big function within your nitrous system. It acts as an orifice to restrict the flow of nitrous and/or fuel into the intake airstream. They install in specially machined fittings and provide a sealing surface once the hose or hardline is attached. The sealing surface is provided by the face of the jet which is machined at a 37° angle so that it mates with AN style fittings.

Types of Jets

A jet is a jet, right?  Well, if you look at a jet as only being a device that provides an orifice to restrict flow, then all jets would be the same.  However, not all jets are created equally.  There are two main types of jets used in the nitrous industry - the ‘Long Stem’ style jet that has a longer and skinnier stem, and the ‘Short Stem’ jet that has a shorter and fatter stem. Both styles of jets are produced in either brass or stainless steel.

Short Stem vs Long Stem Jets and the Location of the Face and Stem

Nozzle Fittings

Much like jets, not all nozzle fittings are created equal.  For instance, a fitting for a short stem jet will not accept a long stem jet and vice-versa.

Our Nitrous Outlet nozzle fittings undergo an additional machining step that allow them to accept both long and short stem jets.  When installing jets in your nozzles, be sure the jet is fully seated against the fitting before attaching the hardline or hose.


Just for informational purposes, our plate fittings will also accept long or short stem jets.  Nitrous Outlet is currently the only nitrous company who's fittings accept both style jets.

Jet Machining Differences

Beyond the differences in stem sizing and the materials chosen, there are several other differences in a jet.  Lets start with the orifice location.  In the image below you can see that even the placement of the small flow-restricting hole can be at opposite ends of the spectrum - literally.  Traditionally, the orifice is near the face of the jet, but some manufacturers place it at the base of the stem.  Diving further in to a "face orifice" jet, there are also the countersinks leading in to the orifice and then out of the stem.  Each manufacturer uses a different size, depth, and angle on the countersink - if they even use them at all.  Now, looking at the stem of the jet, you should see a counterbore that is larger than the orifice.  This counterbore also varies in size and depth depending on the manufacturer.  Using this counterbore exiting the stem creates a "ledge" where the orifice and counterbore meet.

So, by now you're wondering why all these things matter.  Flow - of nitrous and fuel.  The presence of this "ledge" created by the transition from orifice to counterbore and the depth/size/angle of the countersinks can increase flow, or reduce it drastically if the combination of them is wrong.  On our own flow bench, we've witnessed the effect of having a mismatched set of jets and the effect it has on even cylinder distribution on direct ports.  We've also experienced stepping up in jet size to theoretically increase flow only to see flow decreased because the larger jet featured a different machining process.  The opposite can also happen, where a much larger increase or decrease is achieved with a simple jet change.  

This is why jet inspection and selection is so important.



Comparison of Jets. Notice the different tapers leading out of the orifice of the jet and in to the stem.

Jet Selection 

When choosing jets, it’s very important to source them from the same manufacturer because of the differences we just covered. First you want to visually inspect each jet. Make sure the material, face and stem tapers, and even the little ledge inside the jet all appear to be the same.  Once you are confident you have a visually matching set of jets, you’ll want to use a pin gauge to measure the orifice of each jet to ensure they are the same size. Lets talk more about this pin gauge and its usage.

What is a Pin Gauge?

A pin gauge is a small metal rod that’s been measured for accuracy and is used to measure small diameters. There are two types of gauges, a ‘+’ and ‘-’ gauge. The minus gauge will fit into the orifice size you are measuring. For example a .036 gauge will fit into a .036 jet. If the gauge you are using is a plus gauge, the largest you would be able to fit into a .036 jet is a .035 gauge because they are slightly larger than the orifice. Though both type of gauges can be used to measure jets, most people use the minus sets for simplicity. Pin gauge sets are measured and rated for accuracy using one of 4 different ratings:



Pin Gauge Set- Nitrous Outlet P/N 00-56013

Class ZZ- Tolerance of .0002”

Class Z- Tolerance of .0001”

Class X- Tolerance of .00004”

Class XX- Tolerance of .00002”

For our purposes, a set of ZZ rated gauges will work great for measuring even the smallest of jets.  When using a pin gauge on a jet, it’s important to not force a gauge into the jet or it can gouge the inside of the jet and make it unusable. Any damage or irregularity to the inside of the jet will cause it to flow differently. The pin gauge should go smoothly into the jet with no force.


Brass or Stainless?

Depending on who you talk to, you'll get widely varied opinions on which is best and why.  Unfortunately there is no empirical data to support any of them.  Our experiences at Nitrous Outlet have led us to stick with brass simply because we feel it allows a better sealing surface at a lower overall cost.  As we've already outlined, the most important thing you can do for your jetting is visually inspect and pin your jets to ensure you have a matching set - regardless of the brand or material.


This Jet shows signs of corrosion build-up near the orifice.

What Can Damage a Jet?

Besides damaging the orifice with your pin gauge, there are a couple of things that can damage your jets.  Part of your visual inspection should include the face of the jet.  Any dimples, rings, or gouges that catch when you run your fingernail across them will likely cause a leak.  Another common one is that somebody finds an old jet in their toolbox, or acquire some jets secondhand that have deposits on them. The deposits may look dark/rusty, or have a white/green tint to them. If you find or have some jets like this, you can clean them up and they can be reused as long as the sealing face and orifice are in good shape. To clean the jets, soak them in vinegar for a night or two, then brush them off with a small brush or toothbrush and give them a good rinse with fresh water. Be sure to store your jets in a dry place away from any moisture, which can also cause a build-up on the jet. A long term cause of damage to jets is from fuel that contains alcohol. Alcohol is very corrosive and can affect all components of a fuel system, including the fuel jets in your nitrous system. Over time, the alcohol can corrode away the inside of your fuel jets orifice, causing the orifice to get larger and your tune to get richer. For this reason, we recommend inspecting and using a pin gauge on the fuel jets when you inspect the rest of your fuel system on an alcohol powered vehicle.

If you’re having issues with your nitrous system and have checked everything else, take a good look at your jets. If you have a jet that’s causing you issues, it’s always best to replace it. If you have any questions about jets or nitrous systems and accessories, give us a call here at Nitrous Outlet - (254) 848-4300!

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