OPTIMAL NOZZLE JET SIZING
By Scott Offermann and James Monroe

At KillerRONS we are questioned daily regarding nozzle jet sizing in all types of racing applications.  Most of these inquiries are focused upon the specific sizing used to achieve maximum performance and/or consistency.  Often times these questions are brought about when customers compare their nozzle jet sizing to someone utilizing a similar combination.  The intention of this tech bulletin is to explain the process we go through when recommending or choosing a nozzle jet size and also give some insight as to exactly what happens in the engine and fuel system when nozzle jet changes are made.

James Monroe at KillerRONS.COM has had the opportunity to deal with literally thousands of customers over the years and these experiences have helped forge a keen seat-of-the-pants ability to make proper recommendations when it comes to nozzle jet sizing.  The addition of Scott Offermann to the KillerRONS team has brought even more of this experience and knowledge to the company in the last couple of years.  At KillerRONS we know that improvements can always be made so in an effort to further our research and development Scott has assisted in validating these outcomes with simple mathematical equations.  This combination of experience and sound mathematics has helped KillerRONS.COM continue to grow as a company.  This ultimately favors the racer in the end with improved performance and consistency coupled the knowledge of how they got their results.

When discussing nozzle jet sizing the first thing that needs to be understood is that it is nowhere near an exact science.  There are many factors that play a role in the optimal nozzle jet for a given engine application and these factors can be weighted differently even in similar engine combinations.  The main contributors in selecting nozzle jets are engine displacement and horsepower level.  Generally speaking a larger displacement engine with higher power will want a bigger nozzle jets and this is easily formulated with a few simple equations.  Unfortunately it is not that simple as other factors like RPM range, fuel pump make and sizing, racing altitude, cylinder head type and compression ratio play roles in tipping nozzle jet sizing.  This is where experience and continued feedback from customers comes into play. Below we will outline how nozzle jet sizing can affect the performance and consistency of your race car.

Being that our fuel systems are "mechanical" a basic tune-up can be derived via mathematical calculations.  The ratio of orifice area is calculated between the bypass pill and the nozzle jets and then multiplied by the fuel pump output at a given rpm to figure out how much fuel is to be delivered to the engine.  The problem with this is that these calculations alone do not account for the dynamics of what happens in the fuel system while attached to an accelerating engine.  For example math would suggest that a person should keep reducing the size of the nozzle jet along with the bypass pill and still deliver the correct amount of fuel to the engine under the highest possible pressures.  Theoretically this would make more power because better atomization creates smaller droplets of fuel which promotes a more complete burn. This type of tune-up can make more power in some applications but one must be careful as it is a balancing act between achieving adequate atomization and delivering the correct volume of fuel in all situations.  Over the years we have found in on-track testing and feedback that going too small with the nozzle jet will eventually cause the performance and consistency to suffer no matter how much smaller the bypass pill is made to compensate.  When the nozzle jet is border line too small consistency will suffer first and performance will eventually follow.  We will focus on performance first as this is what most noticeable by the racer before the loss of consistency.

From a performance stand point too small of a nozzle jet will cause the engine to accelerate sluggishly through the RPM’s.  This will, without question, affect the elapsed time especially early in the run. This is because the volume of fuel through the smaller nozzle jet doesn't change fast enough as the engine is trying to accelerate quickly.  As the engine RPM's quits changing dramatically and levels off at higher RPM the volume through the nozzle jet stabilizes.  By this time the car is likely in high gear and it will pull well at the stripe producing good MPH.  Consistency suffers in this instance for two reasons.  First an alcohol engine operating border line lean (too small nozzle jet) is difficult to predict as it doesn't do the same thing twice in a row.  Second is that the high volume of smaller droplets (produced by a smaller nozzle jet extreme high pressure tune-up) has more surface area to be influenced by the water vapor in the atmosphere.  For a deeper explanation of how water vapor affects an alcohol engine please read our "Seasonal Performance" tech bulletin here.

A nozzle jet selection that is too large for an engine isn’t typically as detrimental to an engine performance-wise and can still be very consistent.  This is the direction we prefer our customers to error on as we assist them in selecting nozzle jets for their engine.  Depending on the pump and main bypass pill size one must take caution by not selecting a nozzle jet too large for an application.  This can lower the system pressure too much and begin to affect the quality of fuel atomization which will eventually result in poor ET’s and MPH's on the time slip, especially in the "back-half" of the track.

We do our best to provide customers with the best nozzle jet sizing and tune-up for their engine and feel confident that our tune-ups will yield consistent and fast performance at the racetrack.  That being said we also know that every combination is different which means that only testing on your part will yield every last ounce of power and consistency in your engine.  The great news is that the Ron’s drop-in nozzle jets are affordable at $68.50 per set and your engine will typically run well with 2-3 different sizes of nozzle jets.  With that in mind test days can still be competitive race days.  We hope this tech bulletin has helped you understand the role nozzle jet sizing plays in the tune-up and you will use this information as a guidepost for tuning your KillerRONS.COM fuel system.  You can learn more about Ron’s nozzle jet manufacturing and sizing by clicking here.