The North South 100 is one of the marquee events on the dirt late model calendar. Held at Florence Speedway in Kentucky, it draws some of the fastest and most finely tuned cars in short-track racing. But these aren't typical race cars. Late models are a different breed, and that goes far beyond their distinctive bodywork or massive rear spoilers. From chassis flex to power delivery, every part of the setup is specialized including the fuel.
Fuel in late model racing isn't just about making power. It's about managing throttle response on slick dirt, controlling combustion heat in long green-flag runs, and coping with massive compression ratios and high-RPM operation. These engines, often built with aggressive cam profiles and narrow tuning windows, rely on fuels that are chemically stable yet quick to ignite. Inconsistent or poorly matched fuel can cause detonation, lean spots, or even lost horsepower at the worst possible time.
Unlike drag racing or asphalt circle track events, dirt late model races like the North South 100 involve constantly changing traction, variable engine load, and wide throttle modulation. That's why fuel choice here isn't just a technical detail, it's a fundamental part of the car's performance strategy.
Dirt late model engines operate in an environment that's fundamentally different from most other forms of racing. These are high-revving, high-compression V8s that often run over 800 horsepower on tracks that can change texture and grip several times during a single feature. The demands placed on the fuel are significant, both in terms of stability and combustion characteristics.
Unlike paved circuits where grip and throttle inputs are more predictable, dirt track conditions vary corner to corner. That variability means drivers are constantly adjusting throttle, which puts stress on how the fuel responds under partial load, sudden acceleration, and deceleration. A fuel that doesn't respond predictably to these inputs can cause hesitation, misfires, or uneven power delivery, any of which can cost positions or increase engine wear.
The compression ratios found in late model engines are another reason specialized fuel is required. Many of these setups run extremely high cylinder pressures, which demand fuels with not just a high octane number but also a controlled, consistent burn rate. Fuels that are too slow to ignite can soften throttle response, while those with inconsistent detonation resistance can compromise engine safety. These engines don't just need more octane, they need fuel that's matched to the specific pressure and heat profiles found in late model dirt racing.
Octane is often the first number racers look at, but it's only part of the equation. In a dirt late model engine, where compression ratios regularly exceed 14:1 and RPMs run north of 8,000, knock resistance is critical. Detonation under these conditions doesn't just hurt performance, it can end a race or an engine in seconds. That's why fuels for this type of racing must offer not only high octane but also stable knock control across a wide range of temperatures and pressures.
Burn speed is just as important. A fuel that burns too slowly can soften the throttle response, especially when grip is inconsistent and throttle modulation needs to be immediate. On a tacky track, a slow-burning fuel might delay peak torque delivery. On a slick surface, it could make the car feel lazy or vague. Conversely, a fuel that burns too quickly might increase cylinder pressures too early in the combustion cycle, leading to instability or tuning difficulties.
Finding the right balance between octane and burn rate is essential. A well-matched fuel allows tuners to optimize ignition timing and air/fuel ratios without having to compensate for erratic combustion behavior. That means more consistent laps, better drivability out of the corner, and ultimately a more competitive car over a long feature like the North South 100.
Late model engines demand fuels engineered for sustained high speed and high load racing. Two fuels proven in this environment are Sunoco HCR Plus and DXP, each designed to handle the extreme pressures and temperatures of modern oval track racing, though they serve different levels of competition intensity.
HCR Plus (114 octane) is the go-to fuel for most high-compression late models running compression ratios above 14:1. What sets it apart is its exceptional resistance to vapor lock, which means you get consistent fuel metering from the green flag through the checkered flag, critical during hot nights when track conditions evolve. It's sanctioned by Lucas Oil Late Model Dirt Series and other major sanctioning bodies, and it delivers the stability and detonation control that lets you maintain your tune without constant adjustments between heats.
DXP (116 octane) is the choice for teams pushing the absolute limits. Developed for engines with extreme bore sizes, maximum compression ratios, and high rpm levels, DXP delivers extra protection against detonation during the toughest atmospheric conditions. It's built for feature races and endurance events where durability and consistent performance under maximum stress are non-negotiable. The precision blend is engineered to reduce wear in top-level race engines while maintaining the power delivery you need for quick corner exit.
Both fuels are leaded and intended for off-road use. The decision between them depends on your engine's compression ratio, your tuning strategy, and whether you're running a competitive heat race or hunting for a feature win. Weather, track surface, and tire compound all interact with fuel behavior in ways that matter, some teams may find they prefer HCR Plus's consistency in certain conditions or DXP's extra cushion when atmospheric conditions favor maximum power.
FUEL STRATEGY FOR THE NORTH SOUTH 100
The North South 100 isn't just another race, it's a long, grueling main event that tests both driver and equipment over a full 100 laps on changing dirt. Fuel strategy plays a critical role in how well a car performs throughout that span. Unlike shorter heats, where consistency across a handful of laps is the priority, a longer feature race requires fuels that remain stable across varying conditions and engine loads.
Track surface changes dramatically during an event like this. Early in the evening, the surface may be tacky and heavy, putting greater load on the engine and increasing combustion temperatures. As the race progresses, the track typically slicks off, and throttle control becomes more delicate. A fuel that delivers clean, responsive combustion under both conditions helps the driver adapt without needing to change the tune on the fly.
Weather is another factor. Ambient temperature and humidity affect air density, which in turn affects how the fuel burns. A cooler night may allow for more aggressive ignition timing and higher cylinder pressures, while hot, humid conditions require careful tuning to prevent detonation. Choosing a fuel that maintains predictable behavior under these changing variables reduces the chances of tuning missteps.
Fuel performance over a full feature also includes how it handles heat soak and refire scenarios. During red flags or delays, engines may sit with heat building in the intake and combustion chambers. A stable, high-quality fuel prevents vapor lock and ensures clean restarts, critical in a race where track position and timing can shift quickly.
Not all late model engines are built the same, and the type of fuel that works best depends heavily on the internal configuration and class rules. Whether you're racing under an open motor rule set or working within a crate engine class, fuel needs to align with how your engine breathes, burns, and transfers energy to the track.
Engines with extremely high compression ratios and large cam profiles often require leaded fuels with both high octane and fast burn characteristics. These setups benefit from fuels that can tolerate early ignition timing and elevated cylinder pressures without knocking. In contrast, crate engines or sealed motors with limited tuning options might run better on slightly slower-burning fuels that offer smoother throttle response and help maintain drivability on slick surfaces.
Fuel delivery method matters, too. Carbureted engines can be more sensitive to changes in fuel density and vaporization, especially as track temperatures fluctuate. Fuel-injected systems, while often more adaptable, still need consistency in oxygen content and burn rate to avoid calibration issues. Some fuels interact differently with certain cylinder head designs, particularly those that rely on aggressive scavenging or large intake runners.
Understanding how a specific fuel behaves in your engine's combustion environment is key. That includes how it responds to ignition timing, how it atomizes through your intake setup, and how it holds up across multiple laps of hard running. Tuning tools like dyno pulls and data logging are useful for evaluating fuel choices, but real-world track feedback often reveals the subtle differences that separate a good fuel match from a great one.
Race fuel is a precision product, and how it's handled at the track can affect its performance just as much as engine tuning or suspension setup. Dirt late model teams running multi-day events like the North South 100 need to consider storage conditions, temperature swings, and fuel container integrity to ensure consistent performance throughout the weekend.
Most high-octane race fuels are sensitive to air, heat, and light. Exposure to these elements can degrade fuel quality, causing changes in specific gravity, volatility, or octane rating. Fuel should always be stored in opaque, sealed containers and kept away from direct sunlight. On hot summer days, shade or temperature-controlled storage areas can help minimize vapor loss and oxidation.
Vented containers or frequently opened drums are more likely to introduce moisture or contaminants. This is especially risky with oxygenated or ethanol-based fuels, which can absorb water from the air and compromise combustion quality. Teams should use clean, dedicated funnels and pumps when transferring fuel, and seal containers immediately after each use.
Shelf life also varies depending on fuel composition. Non-oxygenated fuels generally last longer when stored properly, while highly oxygenated or ethanol-blended fuels should be cycled more frequently to maintain consistency. Keeping fuel fresh between rounds can help prevent tuning surprises, reduce carbon buildup, and maintain throttle response across long heats or back-to-back race days.
By treating fuel as a controlled component, teams can protect both performance and reliability. Proper storage and handling ensure the fuel behaves the same on lap 100 as it did during hot laps earlier in the night.
Dirt late models may look unconventional, but there's a purpose behind every part of their design, including how they use fuel. These cars operate under extreme conditions: high compression, rapid throttle modulation, and constantly changing track surfaces. Fuel selection in this environment isn't a secondary decision. It's integral to how the car drives, how the engine performs, and how consistently a team can compete across a race weekend.
Choosing the right fuel means understanding combustion speed, knock resistance, oxygen content, and how each of these factors interacts with your engine build. It also means planning for storage, tuning flexibility, and variable track conditions that affect how the fuel behaves under real-world stress.
The North South 100 highlights all of these challenges. It's long, demanding, and often unpredictable—just like the cars themselves. For teams that want to get the most out of their setup, understanding the fuel needs of a late model is just as important as dialing in suspension or tire prep. These cars may be weird, but there's nothing random about the science behind how they run.
For more information on selecting the right racing fuel for your late model, visit Sunoco Race Fuels or use their fuel selector tool to find the perfect match for your engine combination and racing application. As the official fuel of the Lucas Oil Late Model Dirt Series, Sunoco has the experience and expertise to help teams get the most from their late model setups.