We recently visited Bill Davis Racing in High Point, N.C. to answer this question. What we learned was a little surprising, these engines actually have quite a lot in common with street car engines.
Bill Davis racing runs two NASCAR teams, the Caterpillar sponsored No. 22 car and the Amoco sponsored No. 93 car. This year both of these teams are racing the new Dodge Intrepid cars.
Dodge provides the engine block and cylinder head for the engine. They are based on a 340 cubic inch V-8 engine design that was produced in the 1960s. The actual engine blocks and heads are not made from the original tooling, they are custom made race engine blocks, but they do have some things in common with the original engines. They have the same cylinder bore centerlines, the same number of cylinders and the same base displacement. And like the original 1960s engines, the valves are driven by pushrods (see this page for information of the different types of valve arrangements).
The engine in today's NASCAR racecars produce upward of 750 horsepower, and they do it without turbochargers, superchargers or particularly exotic components. So how do they make all that power?
Here are some of the factors:
- The displacement is large -- 358 cubic inches (5.87 liters). Not many cars have engines this big, but the ones that do usually generate well over 300 horsepower.
- The NASCAR engines have extremely radical cam profiles, which open the intake valves much earlier and keep them open longer than street cars. This allows more air to be packed into the cylinders, especially at high speeds (see How Camshafts Work for more details).
- The intake and exhaust are tuned and tested to provide a boost at certain engine speeds. They are also designed to have very low restriction, and there are no mufflers or catalytic converters to slow the exhaust down either.
- They have carburetors that can let in huge volumes of air and fuel -- no fuel injectors on these engines.
- They have high intensity programmable ignition systems so the spark timing can be customized to provide the most possible power.
- All of the subsystems like coolant pumps, oil pumps, steering pumps and alternators are designed to run at sustained high speeds and temperatures.
When these engines are assembled, they are built to very exacting tolerances (parts are machined more accurately), so that everything fits perfectly. Cylinders are bored to more exacting tolerances than street cars. The crankshafts and other rotating parts are balanced. Making sure that the parts are as close to their exact dimensions as possible helps the engine achieve its maximum potential power and also helps reduce wear. If parts are too big or small, power can be lost due to extra friction or pressure leakage through bigger than necessary gaps.
After the engine is assembled, it runs on the dynamometer (measures engine power output) for 30 minutes to break it in. The engine is then inspected. The filters are checked for excess metal shavings to make sure no abnormal wear is taking place.
If it passes this test, then it goes on the dynamometer for another two hours. During this test, the ignition timing is dialed in to maximize power and the engine is cycled through various speed and power ranges.
After this test, the engine is inspected thoroughly. The valve train is pulled and the camshaft and lifters are inspected. The insides of the cylinders are examined with borescopes (inspects the interior using mirrors). The cylinders are pressurized and the rate of leak down is measured to see how well the pistons and seals hold the pressure. All of the lines and hoses are checked.
Only after all of these tests and inspections are finished is the engine ready to go to the races. Insuring the reliability of the engine is critical -- almost any engine failure during a race eliminates any chances of winning.
Here are some interesting links: