A Nitro Funny Car in short, the engines can only be V-8s at 90 degrees. (The most popular design is loosely based on the 426 Hemi.) There can only be two valves per cylinder and superchargers are restricted to a basic Roots type—19 inch (483 mm) rotor case length with a width of 11.25 inches (286 mm). The engine displacement can be a maximum of 500 in„ (~8.2 L). Only single camshafts are allowed. There are two common bore-stroke combinations: 4.1875 × 4.50 inches (106.4 × 114.3 mm) (called a 3/4 stroker) and 4.25 × 4.375 in (108.0 × 111.1 mm) (called a 5/8 stroker). The 3/4 stroker is the most common combination used today and equals 496 in„ (8.1 L).
Engine blocks are usually made out of aluminum billet. Crankshafts are made from steel forgings. Intake valves are titanium and of 2.40 inch (61 mm) diameter, while exhaust valves are 1.90 inch (48 mm) diameter made out of Inconel. Every funny car has ballistic blankets covering specific parts of the engine prone to explosion.
Funny car fuel systems are key to their immense power. Most systems will deliver from 500 to 600 pounds-force per square inch (3 to 4 MPa) of fuel pressure at as much as 75 U.S. gallons per minute (5 L/s). During a single run (starting, burnout, backing up, staging, 1/4 mile) cars can burn as much as 15 U.S. gallons (57 L) of fuel. The fuel mixture is usually 85–90% nitromethane with 10–15% alcohol. The ratio of fuel to air can be as high as 1:1. Compression ratios vary from 6:1 to 7:1. The engines in funny cars commonly exhibit varying piston heights and ratios that are determined by the piston's proximity to the air intake. Funny cars have a fixed gear ratio of 3.20:1 and have a reversing gear. Wheelbase is between 100 and 125 inches (2.54 and 3.18 m). The car must maintain a 3 in (76 mm) ground clearance.
Horsepower claims vary widely—from 7,000–9,000—but are probably in the 8,000 BHP range. Supercharged, nitromethane-fueled motors of this type actually derive their quick elapsed times and stratospheric speeds from their torque which is estimated at about 7,000 ft…lbf. They routinely have a 5g acceleration from a standing start.
Many safety rules are in place to protect the driver, spectators, and others. The more visible accoutrements are the twin parachutes to help stabilize and decelerate the car once it crosses the finish line.
The first funny cars were built in the mid-'60s and so-called because the front wheels had been moved forward on the chassis to improve weight transfer under acceleration, increasing traction on the rear tires which were over sized compared to stock. Looking at the cars, they didn't quite look stock, hence the name "funny." Many of the older cars are still raced today in the NHRA Heritage Hot Rod Racing Series, including the National Hot Rod Reunion and the California Hot Rod Reunion.