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How a Sprint Car Works

A Beginners Guide to Sprint Cars
by Al Drake and Craig Smith

This is guide for the casual fan that would like to know how a sprint car works and what the various parts are on the car. Entry level education on the terms will help you at the race track when the announcer says "this broke" or a driver says he had a problem with "that" during an interview.

The Chassis

In this case, the chassis is manufactured by J&J Chassis Company. It is called a "downtube chassis" because it has tubes that run from the top of the roll cage down to the front of the car. This provides stiffness to the chassis and limits flex more than a chassis that does not have the tubes (primarily older cars). The chassis is made of chrome-moly steel tubing. The tubes are welded together in jigs that allow the manufacturers to create a consistent line of cars.

The Drive Line

To start, sprint cars don't have a transmission. They are either in gear or out of gear. The cars used to have an in\out box (sometimes clutch-actuated), but now days, there is a t-handle on the end of a cable that runs down to the rear end. The gears are in the rear end and if you pull the cable, the gears disconnect. The gears in the rearend determine how fast the car can go and how hard the engine has to work to drive the wheels. A plate on the rearend can be removed and the gear sets can be changed to match the length of a given track (and its conditions)

The driveshaft is a solid bar that runs from the engines crankshaft to the rear end. The torque tube is a pipe between the engine and rear end that the driveshaft spins inside of. There are universal joints at both ends that let the driveshaft turn when the rear axle moves up and down. The torque tube is mounted to the rear end and at the engine slides into a swiveling ball housing.

The Engine

Engines in sprint cars come in primarily two sizes: 360 cubic inch and 410 cubic inch displacement. Some divisions require an iron (or stock) block, while other divisions allow aluminum. The internal parts of the engines in some cases have titanium parts, but require more maintenance. Most divisions of sprintcars use fuel injection (as opposed to carburators). They dont have a distributor like a passenger car, sprintcar engines use magnetos. Magnetos are run with an on\off switch and require the engine to be turning over to start a spark. There are no batteries on sprintcars, they have to be push started. When the car is in gear and pused by a truck, the oil pressure comes up, the on\off switch is turned on which "lights the mag". The engine "fires off" and the car accelerates away from the push truck. The oil in the engine is distributed by a dry-sump system. In todays cars, the dry sump tank is mounted on the front of the engine next to the water pump. The engine is mounted to the chassis in the rear by a motorplate. The fuel pump and driveline stick through the motorplate and reside between the drivers legs! Its a tight cockpit with all the pumps, hoses and pedals. Also in the pump housing is the pump that pressurizes the brakes.

Sometimes the cars do not run mufflers and are very loud. At most races though, there is a sound limit which varies in decibels at 100 feet distance from the car. It's still plenty loud!

The Suspension

Suspension on a sprint car is called 4-bar torsion. There are two torsion bars in front and two in back. One bar springs each corner of the car. The torsion arm is on the end of the bar and supports the axle on that corner. On the other end of the bar is a piece called a torsion stop. It clamps to the bar and rests against the frame so the torsion bar wont spin. While the torsion arms determine the upward movement of the axle, the shock absorber keeps the axle from falling out the bottom. It's attached at the top to the frame and attached to the axle at the bottom. Right to left movement is limited by the panhard rod which mounts one end to the frame and the other to the axle. It's like a hinge, but keeps the axle in place. The other parts to the front suspension are the radius rods. They mount one end to the side of the car and the other to the axle. This locates and squares up the axle so it wont move front to back.

In the rear of the car, the same design technology is used, but instead of a panhard rod to stabilize the right-left movement, a piece called a jacobs ladder is used. It's a "w" shaped piece. The two ends of the "w" are mounted to the chassis and the center peak is mounted to the the birdcage. A birdcage contains the rear wheel bearings that the axle rides in and provides mounting points for the shock absorbers as well. 

The shock absorbers on a sprintcar are special items. They are designed with different rebound and compression rates to make the car soft, or hard and keep the wheels on the ground. If the wheels are not on the ground, its bad news!

The Brakes

Sprint cars use disc brakes. In the front of the car, there is one disc on the left wheel and thats it! In the back there is on behind the drivers seat on the rear axle (under the fuel tank) and sometimes one on the right rear wheel. When the car is fast and the driver drags the brakes in the turns, they glow orange, sometimes they throw sparks.

 

The Wings

Sprintcars did not always use wings, but in the 1970s they began to show up. In the beginning they were huge! Todays series limit wings on top of the car to 25 square feet (5'x5' in most cases). They as well as the smaller nose wings are mounted to the car with tubes called spuds. Some divisions allow sliders on the top wing which allow the driver to move the wing back and forth using hydraulic levers. In a track is fast and heavy, the wing will be forward, if the track is dry, the wing will be moved back. If a division does not allow sliders, the team has to position the wing before the race to a spot and angle that they think will make the car handle the best in the closing stages of the race.

The Steering

Driving a sprintcar these days requires power steering. The steering wheel is made of lightweight metal and has a quick-disconnect hub for easy removal. The steering box it mounts to is right above the drivers knees and exits the left side of the car to a lever it rotates called a pitman arm. The pitman arm has holes in it to adjust how much steering input is required to turn the cars front wheels. The pitman arm is connected to a bar called a drag link. The drag link connects to the left front spindle and then another bar goes to the right front spindle that is used to not only turn both wheels at the same time, but also allow alignment adjustments to be made.

The Fuel

Most sprintcars use methanol. Some use pump gas, but not many. Sprint cars carry a fuel cell in the back of the car that looks like a bumble bee's tail. The capacity ranges on the tanks, some use 30-35 gallon tanks, while others use a 24 gallon tank. Less is lighter but if you run out of gas during the race, there is no time to refuel and you're done for the night.

 

The Cockpit

By now, you have a pretty good idea what the environment is like. The driver sits in a custom fitted high-back aluminum seat with 4" wide belts in a 5-point harness configuration. With the belts on and tight, you don't go anywhere. As you sit in the car, the driveline and some pumps are between your legs, fuel lines from the tank come from behind you and wrap around to the right and into the pumps. The brake pedal is on the left and is a swing arm type lever. The gas pedal is a spring loaded stirrup and on the right. Ahead of the steering wheel is the dashboard. On the dashboard is the oil pressure and water temperature gauges. Also on the dash is the mag switch and a fire extinguisher switch. There is also a fuel mixture knob to lean out or richen up the engine. To the left of the steering wheel is the wing slider lever. 

Plenty to do! But wait there's more!

The driver wears a nomex firesuit with nomex underwear. Shoes and gloves are also special fireproof material. It doesn't breath very well and the driver is pretty warm and sometimes sweaty by the end of the race (even on a cool night!). The driver wears a nomex hood on his head and then puts the helmet on. Claustrophobic yet? With all this on, and strapped into the car, many drivers put a foam collar on below the helmet that keeps their head from bouncing around. Looking down is not an option. Left and right motion is about it. With the helmet visor down, the driver now has tear-off strips of plastic on the lens he can reach up and remove when the dirt gets too thick to see. Now think about working all those levers on a 3/10-mile dirt oval averaging 95 mph and reaching up to pull a tear-off!

Anatomy of a Sprint Car
 

Modern sprint cars are simple and brutally powerful.  There is no dead weight on the car; if a part doesn't contribute to the car's performance, it is left off. The chassis is a minimal tube frame with a short 84-inch wheelbase. The suspension, deliberately crude by modern standards, consists of a live axle in the rear and a dead axle up front, and torsion bars for springs. A V8 engine, fueled by methanol, is connected to the quick-change rear axle by a coupler called an "in-out box". There's no starter motor, and the battery is only large enough to power the ignition system for the evening. Two huge floppy rear tires of different sizes couple the irresistible force to the soft clay below. The driver sits atop the rear axle, his legs straddling the drive shaft. With a power-to-weight ratio comparable to a Formula 1 racer's, and a short, tipsy frame, a sprint car spends most of its time scrabbling for traction, broadsliding around the corners, wheelstanding on the straights, and throwing clay into the stands, while the driver wrestles frantically with the steering wheel.

 

The power plants

 

In the golden era of the 1950s and early 1960s, the standard sprint car engine was the classic double-overhead-cam, 4-valve-per-cylinder, 4-cylinder Offenhauser. The 255-cubic-inch Offys made a low-pitched guttural roar that few who ever heard it have forgotten. But during the 1960s, the Chevrolet small block V8 became popular. Originally these were cast-iron 283 and 327 cubic inch engines, with 2 valves per cylinder actuated by pushrods and rocker arms, little different from street Corvette motors of the era. As the racers searched for more power, the Chevy V8 was bored and stroked until displacements exceeded 400 cubic inches, and the iron castings gave way to purpose-built aluminum blocks and heads.

 

The Outlaw's Choice: The 410

The standard power plant of professional sprint car racing today displaces 410 cubic inches, and is based on aluminum blocks from Donovan or Rodeck, and aluminum heads from Brodix. The basic dimensions (bore center spacing, deck height, etc.) are still those of a Chevy V8, but you won't find a single GM part in the engine. Roller tappets and rocker arms actuate the titanium valves. Tall injector stacks top it off, feeding a potent mix of methanol and air to the cylinders. More fuel is injected through "down nozzles" in the side of the heads (see photo above). Oiling is handled by a dry sump system, with the oil tank often located just ahead of the driver on his left. These engines routinely top 8000 RPM, producing in excess of 800 BHP! The most potent of these engines are built by Ron Shaver and Earl Gaerte, whose motors power most of the winners on the World of Outlaws tour and regional series around the USA. These finicky machines require an overhaul after 8 to 10 evenings' work. As with all else in sprint car racing, there are engines, and then there are Outlaw engines. To run with the Outlaws takes a little more motor than you'll find at most tracks. And even among the Outlaws, there are regular engines, and there are special engines built for the high-buck races like Eldora Speedway's King's Royal and The Big One (with $50,000 and $100,000 to win respectively), and sprint car racing's most prestigious event, the Knoxville (IA) Nationals. These expensive hand grenades are built extra hot, and may only survive one night's racing. But if they bring home the winner's prize, they're worth it!

 

Daring to be different: Ford power

In the 1980s, long-time team owner and Ford dealer Casey Luna became frustrated with the fact that he had to run a Brand X motor, and funded development of an aluminum sprint car engine based on Ford's potent 351 Cleveland V8. Like the "Chevy" engines, the "Ford" sprint car engine block and heads are actually cast by outside suppliers, usually Fontana or Alan Root.

In 1989 Luna finally achieved his goal of winning the World of Outlaws championship with this creation, with Bobby Davis Jr. driving. This was the year of the infamous World of Outlaws - United Sprint Association split, so some might question the validity of this trophy. But in 1996 Luna's Ford-powered sprinter won the title convincingly, with Dave Blaney at the wheel of the Vivarin #10, and no asterisks to be found anywhere! Though other teams (notably Danny Pivovaroff's #19 CRA/SCRA sprinter) have used Ford motivation in recent years, Luna's creation, now in the Two Winners team's #104+ WoO sprinter driven by Jeff Swindell, is at present the only one I know of using Ford power.

 

Methanol fuel and its implications

The fuel systems of these aluminum brutes deserve a closer look. Methanol has been used as a racing fuel in the US since 1927, because it offered an octane rating of around 114 when the gasoline of the day was only capable of 60 or so (that's where "Phillips 66" got its name, from its high octane rating!). The substantially higher compression ratios possible with methanol resulted in equally substantial horsepower boosts in the early days. Modern racing gasoline has caught up on octane, but methanol has key safety advantages that keep it in the forefront of American racing. Methanol is easily diluted by water, making an alcohol fire easier to put out than a gasoline fire. And it burns cooler and more slowly than gas, which means it is easier on engine parts. But methanol also has a lower energy density than gasoline, requiring almost twice the volume to feed the same size engine. It can be difficult to squirt enough fuel in through the intake ports! This huge thirst also requires relatively large tanks. The typical sprint car carries a 30 gallon (US) tank -- and it's not unusual to see fuel stops in a 30 lap race if there have been several cautions! Because the engine compartment is tight, many sprint cars mount the high pressure fuel injection pump behind the firewall, in the driver's compartment. This has obvious risks, especially when you consider that the drive shaft is directly below! Some years ago on a televised sprint car race, Gary Bettenhausen was burned when the drive shaft flew off and knocked off part of the pump, spraying fuel all over Gary and soaking his fire suit. Fire crews quickly extinguished the flames, but Bettenhausen's burns took quite a while to heal.

 

The 360: Budget power for the weekend warrior

At US$25,000 or more, the price of competitive power is too steep for many who race sprint cars as a hobby. Tracks throughout the US have recognized this, and sanction races limiting engines to 360 cubic inches. In much of the US, this is the standard local formula. Typical 360 rules are based on production cast-iron blocks and heads, using a wet sump in place of the expensive dry-sump system, and forbidding down nozzles. These restricted engines are typically much cheaper to build at around US$10,000. Some associations add further restrictions; the American Sprint Car Series rules are typical of many "spec head" series, head porting being one of the big expenses in building a competition engine. These lower-priced engines have become popular with local racers, since the 360s can still crank out enough power to shower the stands with clay. Despite the lower power and increased weight, the 360-powered sprinters lack none of the excitement of their more expensive cousins. And on tighter or slicker tracks where traction is at a premium, 360s can run competitively with the 410s.

 

The V6 alternative

Another option in some sanctioning bodies is V6 power. USAC made V6 power legal some years ago when it appeared Detroit was going to phase out the V8 due to fuel economy concerns. While they were at it, USAC also gave the V6 a healthy weight break, so that V6-powered cars would have not only a competitive power-to-weight ratio, but a edge in cornering as well. V6-powered sprinters have won a number of USAC non-winged races on pavement. And Kurt Martin of Chico, CA reports that Mark Hall's #54 is a consistent winner on the Northern California 360 circuit with a 317 cubic inch Chevy V6. So these lighter, cheaper motors are a viable option on the smaller tracks.

 

Winged and non-winged sprint cars

Most sprint car racing today is done with a huge 5-foot-square (25 square foot) aluminum wing mounted atop the roll cage, and a 2-foot by 3-foot wing above the front wheels. The top wing's location can be adjusted by means of a hydraulic "slider", moving the aerodynamic center of pressure to compensate for changing track conditions. Here again, some organizations attempt to limit costs by restricting the size of the wing (16 square foot top wings are required by Petaluma (California) Speedway and the URC), some ban hydraulic sliders, and some prohibit sliders of any sort. Winged sprint cars started appearing at unsanctioned "open competition" races as early as the 1960s, and became wildly popular with fans throughout the US, over the objections of sanctioning bodies like USAC. Soon these "outlaw" racers were popular enough to form their own series, and the World of Outlaws tour was organized. As in other forms of auto racing, the wings provide negative lift or "downforce" to help the car stick to the track. The large end plates also act like the feathers on a dart, helping the car stay pointed in the right direction and keeping it from getting too far sideways. Another benefit of the end plates is the advertising space they provide for sponsors. This is especially important when you consider the difference between the cost of running a sprint car and the typical prize money at most tracks; no one makes a living on their winnings alone. Most racers think the aluminum wing adds valuable crushable structure, cushioning the blow when a sprinter turns over. Many race drivers would gladly destroy a $500 wing to avoid a hospital stay! It is for this reason alone that non-winged sprinters are banned at tracks like Calistoga, CA. There's no denying that winged sprinters are fast. The current lap record at Eldora Speedway, a heavily banked 1/2 mile clay oval in Ohio, is in excess of 120 MPH! Watching these cars run in humid air is an awesome sight, contrails following the racers down the straights, the engines straining and roaring against the aerodynamic load.

But purists like me prefer our racing without wings. Not only do you get a better view of the driver at work, but the traction is harder to find. The cars get further sideways and spend more time sideways, putting a premium on driving talent and opening up a variety of different racing lines. Despite the slower lap times, many fans find non-winged sprint car racing offers more side-by-side action.

 

Wings and engine tuning

Winged cars require different engine tuning than non-winged sprinters. Downforce isn't free; the wing generates drag as well. The winged cars obviously require all the power the engine can deliver, limiting straightaway speeds. But the downforce means the cars can corner faster, so the average speed is much higher, and the engine tends to work in a fairly narrow power band. At some tracks, under ideal conditions, the driver never has to back out of the throttle! Motors for winged cars tend to be tuned for maximum horsepower as a result.The non-winged cars, on the other hand, lack the traction advantage of their winged cousins. And because the cars go slower in the corners, generate more wheel spin, and tend to be steered with the throttle more, smooth part-throttle response and controllability are often more important than maximum horsepower. Lealand McSpadden was quoted in an Open Wheel magazine interview as saying he couldn't apply full throttle until he was 3/4 of the way down the straightaway at some tracks. So engines for non-winged cars tend to have a wider operating range, broader torque curves, and often lower peak horsepower than those in winged sprint cars.

 

This information was reproduced with permission from - Chuck Fry. Visit his website 

 

 

 

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