Stand in the middle of fifty idling Sprint Car Engines and you can literally feel the horsepower in the air. Rumbling inside the Sprint Car chassis rails, the V8 engines shake the ground and fill the air with the sweet aroma of methanol. Once released onto the track, Sprint Car Engines are capable of producing huge amounts of horsepower, in fact a decent 410ci engine is capable of hitting over 810hp.
Positioned only inches in front of the driver’s knees, the big V8s power the cars to speeds in excess of 150mph. Having evolved from the legendary Chevrolet small block V8, today’s Sprint Car Engines are purpose-built racing engines. Engine sizes and configurations vary depending upon the rules of the various governing bodies, however the 410ci is the most popular engine size utilized around the globe. The 360ci engine, as used by the ASCS, provides a cheaper alternative for budget racers. The 358ci engine is popular in central Pennsylvania, competitors in this section are limited to steel blocks and heads.
Teams on the World of Outlaws series will usually have at least six motors in their program, each costing around US$50,000. On the other end of the scale, a new 360ci engine will set you back around US$30,000.
Aluminum blocks are preferred when building a Sprint Car Engine, not only do aluminum blocks have a weight advantage over steel, they are also stronger and can be repaired if necessary. Manufacturers of Sprint Car blocks include Donovan, Rodeck, Dart, Brodix and Mopar.
Cylinder heads are extremely important to the overall performance of an engine. Many hours of development are spent on cylinder heads, experimenting with valve angles, port heights etc. CNC machines are now used by most engine builders to accurately port cylinder heads. Once again, if allowed, aluminum heads are preferred. Popular cylinder head manufacturers include Dart, Brodix and All Pro.
The valve train design of the modern Sprint Car Engine remains the same as the original Small Block Chevy, a single cam lifting 16 pushrods, which in turn open the 16 valves via the rocker arms. Despite this, today’s engines are able to rev higher and produce much more horsepower, thanks to improved manufacturing techniques and the use of alloys and metals such as titanium. Where allowed roller lifters and rockers are used as are titanium valves, which reduce weight and improve longevity of the parts.
The oil system in a Sprint Car Engine is typically a dry-sump system, where the oil is stored in an oil tank and the oil is circulated through the engine using a system of pumps. There are numerous advantages of using a dry-sump system to the conventional wet-sump. Dry-sump systems allow the engine to be mounted lower in the car due to the fact that the oil pan is 4 to 5 inches shorter than a wet-sump pan. Placing the engine lower in the car will lower the center of gravity, and also allow a lower hood line. A dry-sump system allows the easy adjustment of the amount of oil in the system and the speed with which the oil is circulated. Benefits also include possible increases in horsepower, where the scavenge pumps of the dry-sump system create a vacuum inside the crankcase, allowing the piston rings to seal more efficiently.
Methanol, also known as alcohol, is the fuel of choice in Sprint Car Racing. Methanol is used in Sprint Cars for a number of reasons, one being the safety factor. Methanol is less volatile than gasoline, reducing the risk of explosion or flash fire. If a methanol fire does occur it can be extinguished using water. Methanol also burns cooler than gasoline, which assists with the cooling of the engine.
Fuel is fed to most Sprint Car Engines via fuel injection. Known as a “Constant Flow” System, the system uses a mechanical fuel pump to increase/decrease the supply flow to the injection unit directly related to engine rpm. Teams can quickly change the amount of fuel being fed to the cylinders by changing what is known as a “Pill” or by-pass jet, the larger the jet size, the more fuel is allowed to return to the tank, thus, the engine will receive less. To richen the mixture, a smaller jet size is used. To lean the mixture, use a larger jet size is required. As fuel pressure relates to engine speed, a high speed jet is also required to release fuel to the tank at a set pressure. Electronic fuel injection systems are generally not allowed in Sprint Car Racing.
Spark is supplied to a Sprint Car Engine via a magneto system, which is designed for cars that burn alcohol and do not utilise a battery. Connected to the magneto is the transformer or points box, this is normally mounted to the firewall. MSD and Mallory are leading manufacturers of Sprint Car Racing ignition systems. Some modern ignition systems feature rev limiters that limit the revs in the event of driveline failure or a wreck.
Engine management systems are not allowed in Sprint Car Racing.
Sprint Car Engines use a simple cooling system comprising of a water pump and an aluminum radiator, no fans etc are used.
Changing the Engine
In the event of an engine failure a good Sprint Car team can change engines in around 15-20 minutes. This means that a team could lose an engine in qualifying and still make it out for the first heat. This is thanks to the simplicity of Sprint Car design, just remove the throttle, fuel and radiator lines, unbolt the headers, unplug a few leads, unbolt the engine and out she comes!
Routine engine maintenance is very important to ensure reliability and longevity of a Sprint Car Engine. Sprint Car teams thoroughly clean and check the engine after every show. Regular checks include valvespring pressures, valve lash and even conducting a leakdown test to ensure proper valve and ring seal. Oil filters are checked for debris and injector nozzles are removed cleaned.
“Rev Motors” or “Hot Motors” are used by the big budget teams to compete at high paying shows such as the Kings Royal and the Knoxville Nationals. These motors are built for speed, not longevity, and may only last for a few nights before requiring a rebuild. Using high compression and very low tolerances, Rev Motors are capable of hitting around 9,000 rpm.
Intervals between engine rebuilds vary depending on how hard the engine is being worked, but a usual interval is around every 15-20 shows. Most rebuilds will include new pistons, bearings, rings, valve springs and gaskets. The rods and crankshaft should be crack tested and replaced if necessary. The heads will get a complete going over, and the fuel pump should be flow tested.