When you hear the term “Sprint Car,” everyone in the short-track world knows what they are. They’re loud, incredibly fast, on the edge of reckless abandon, and are violent at times. They are the cars that everyone walks up to the fence to watch, regardless of why they came to the track that night. What makes them special? Let’s dig into the basics to find out what makes these race cars tick.
Four Main Types
Sprint Cars, for the most part, are categorized into four-major types. Although there are a lot of sub categories, these are the top-4 that make up most of the car counts across the country. There are 360ci-engine based non-wing and 360ci winged cars, 410ci-engine based non-wing, and the very popular, 410ci winged cars. These are obviously categorized by engine size, and by winged and non-wing variations. The 360 engine classes are supposed to be the more economical class, and the stepping stone into the fire-breathing 410 classes.
You might be surprised to learn that the difference in speeds aren’t as big as you might think. Non-wing cars don’t have the downforce applied to them that the winged cars have, which makes them considerably over-powered versus weight and grip. This makes for awesome displays of wheelies, bicycles, and slide jobs. Winged cars on the other hand, use a huge amount of downforce, which allows them to utilize the incredible power the 360 and 410 methanol-burning engines create, which equals unbelievable speeds and breath taking moves that appear to be in fast-forward mode.
The 360ci engine rules vary across the country, but most are consistent with stipulating cast-iron blocks and aluminum heads. Mechanical fuel-injection introduces methanol fuel into the cylinders through air stacks, and not directly into the cylinders like the 410s. Some sanctioning bodies dictate a specific block and or head combination as well. This is done to try and keep cost down and the competition close. All internals are to be magnetic (ferrous), no titanium or lightweight Space-X materials are allowed. The typical horsepower range on a 360 is 600 to 700 horsepower, depending on the rules package.
The larger 410ci engine rules are a little more open. You must be under the cubic-inch maximum of course, but aluminum block and head combinations are virtually unlimited. Depending on what type of horsepower or torque curve you are looking to achieve, part selection will dictate what combination of air and fuel consumption you create. Electronic Fuel Injection (EFI) is not allowed, but direct injection into the cylinders is, which is much more efficient at atomizing the methanol than if injected though the injection stacks. This means you can run much bigger air stacks and valves to allow your engine to breath and create power more efficiently. Magnetic internal components are required in the 410 classes as well. The typical horsepower range for a 410 engines is 800 to 900 horsepower, depending on the rules package.
Chassis on both the 360 and the 410 cars are exactly the same size. There are differences between a winged and non-wing car as far as the setups are concerned, but for the most part, the chassis manufacturers try to create one car that accommodates both styles, for cost purposes. This allows a racer who wants to compete in both classes to do so with the same vehicle. Most sanctioning bodies have adopted the same safety requirements of minimum wall-thickness around the driver compartments so these cars can go from racetrack to racetrack with no problems.
Most current sprint cars utilize torsion bars on all four corners of the car, although some do use coil springs on the front. Some non-winged cars also use a fifth torsion bar on the front as a sway bar to build left-rear bite when coming out of the corners. Torsion-bar lengths vary depending on the chassis manufacturer. The shorter the bar, the faster it will react (twist back to its normal state). The longer the bar, the slower it will react. Changing the length of the bar on different corners of the car can affect the feel of the car.
Torsion-bar technology has not changed a whole lot, but manufacturing processes and materials have continued to evolve, helping to produce a superior product with longer life expectancy. What has changed, is the evolution of stacking bumpstops (or bump springs) with the current torsion bar and shock packages. This allows a car to carry a softer initial spring rate so it can travel and build mechanical grip while at slow speeds (or when the track gets slick), yet stop the car from rolling too far by adding needed spring rate to meet a desired wheel load when the car gets to speed and aero loads increase.
Watt’s Link, Panhard Bar, And Radius Rods
All sprint cars use a Watt’s link in the rear to hold the solid axle in the center of the chassis while allowing it to articulate up and down. A Panhard bar holds the solid front-axle centered in the chassis while allowing it to articulate up and down as well. Both the Watts link and the Panhard bar have available adjustments to change the roll center depending on driver preference or track conditions. Most cars utilize a two-radius rod setup or “Z”-bar in the rear, using one torsion arm attaching the torsion bar to the bottom of the birdcage, and one attaching the top of the birdcage to the chassis. This is the same technology that has been around since the ’50s and ’60s. Typically, in the front, they use three radius rods to hold the axle perpendicular and upright. This is where you would adjust the squaring of the axles as well as the caster of the front axle.
The basic shape and functionality of a sprint car really has not changed a whole lot in the past 40 to 50 years, but certain components have. Sure, the bodies make them look different than they used too, but the engines have probably seen the biggest evolution of change, jumping somewhere in the range of 200 horsepower since the early ’80s. The next biggest jump in technology would have to be shocks. As horsepower increased, obviously, so did speed. Most parts on the cars had to evolve as well, in order to keep the tires from spinning too much, and make them comfortable enough to drive. These engines are so powerful, they can easily overpower the car and make it a handful to drive if not set up properly.
Shock dynos have changed the racing world. What was once only available to top forms of racing like Nascar and Formula 1, quickly became affordable enough for the short-track racers and shock builders to use. This allowed teams to collect data and really see what was going on within their shocks, instead of using the old method of standardized compression and rebound ratings which varied from builder to builder. Along with this, came the evolution of internal shock parts and pistons with endless combinations of shim stacks to go along with them. The modern shock is probably the single-most-important tuning tool a team has in its arsenal. Compression load numbers (distance traveled x spring rate) are very valuable, but just as valuable, is static load numbers and extended load numbers. These all come into play as the car goes from idling around the track to hyperspeed and aero loads in only a few seconds.
Tires are another part of the car that can be completely overlooked. Most sanctioning bodies have a spec brand of tire, and maybe one or two compounds that you can choose from. That does not mean they all show up the same on race day. Tire prep is a key part of the setup of any race car. Every tire has a heat operating range in which they perform best, and if you exceed that, you will be disappointed sooner rather than later. Air pressures, cutting, and siping all play into this, as well as certain forms of legal chemical prepping, sanding, grinding, and air pressure. If you get this combination right, you will have one happy driver, if you get this wrong, you will hear the typical “would haves or should haves” if the tires gave up.
The last thing I would like to discuss are the safety components of Sprint Cars. This is a very touchy subject, because to the hardcore sprint car fans, they love to see things evolve, but also stay traditional. As speeds have increased, we have added containment seats, Hans and other head and neck restraints, better belts, caps to hold the torsion arms, straps to hold the driveline better, straps to hold steering arms and radius rods, and fuel bladders and tanks have been improved. The one thing that still hasn’t changed is the cage size around the drivers’ compartment, and a lack of head protection. That’s an area that probably should be brought into modern standards.
In a nut shell, we touched base on what makes a Sprint Car tick, the different types of Sprint Cars, some of the changes that have taken place recently, and some of the changes I think need to happen. Sprint cars are (and always will be) badass pieces of machinery, with the guys that drive them even more badass. But regardless, if you’re a fan of Sprint Cars, Modifieds, or Hobby Stocks, please get out and support your local tracks. That’s the only way we can keep enjoying this pastime that only we in America know how to do right!