Guidelines
The NHRA has strict guidelines for funny cars. Most of the rules relate to the engine. In short, the engines can only be V-8s displacing no more than 500 cubic inches (8.19 L). The most popular design is loosely based on the second generation Chrysler 426 Hemi "Elephant Engine" made from 1964-71.
There can only be two valves per cylinder. The heads are machined from a solid block of billet aluminum and have no water jackets, as the high latent heat of the methanol in the fuel coupled with the brevity of the run precludes the need for water cooling of the cylinder heads. Superchargers are restricted to a basic Roots type—19-inch (480 mm) rotor case width with a breadth of 11.25 inches (286 mm). The rotors are not allowed to have more than a certain amount of helical twist in them so the blower does not become a screw-type supercharger in function. Only single camshafts are allowed. There are two common bore-stroke combinations: 4.1875 by 4.50 inches (106.36 mm × 114 mm) (called a 3/4 stroker) and 4.25 by 4.375 inches (108 mm × 111.1 mm) (called a 5/8 stroker). The 3/4 stroker is the most common combination used today and equals 496 CID (8.1 L).
Engine blocks are usually made out of billet. Crankshafts are CNC machine carved from a single piece of steel billet then nitrided in an oven to increase surface hardness. Intake valves are titanium and of 2.40-inch (61 mm) width, while exhaust valves are 1.90-inch (48 mm) width of Inconel. Every funny car has ballistic blankets covering the supercharger because this part of the engine is prone to explosion.
Funny car fuel systems are key to their immense power. During a single run (starting, burnout, backing up, staging, 1/4 mile) cars can burn as much as 15 US gallons (12 imp gal; 57 L) of fuel. The fuel mixture is usually 85–90% nitromethane with 10–15% methanol. 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; power is transmitted from engine to final drive through a multiple staged clutch which provides progressive incremental lockup as the run proceeds. The rate/degree of lockup is mechanically/pneumatically controlled and preset before each run according to various conditions, in particular track surface. Wheelbase is between 100 and 125 inches (2.5 and 3.2 m). The car must maintain a 3-inch (76 mm) ground clearance.
Horsepower claims vary widely—from 6,978 to 8,897—but are probably around 8,000 HP. Supercharged, nitromethane-fueled motors of this type derive their extremely high speeds from their torque, which is estimated at about 7,000 ft·lbf (9,500 N·m). They routinely achieve a 6G acceleration from a standing start.
Read more about this topic: Funny Car