NHRA Top Fuel Engine Specifications

by Phil Whitmer

NHRA Top Fuel dragsters are the world's fastest accelerating land vehicles. They can go from 0 to 60 mph in half a second. The lightweight drag rails can travel a quarter-mile in 4.4 seconds while achieving speeds of more than 335 mph. They are the most famous and recognizable class of drag racing cars, known around the globe. The engines operate under such stressful conditions they must be torn down and rebuilt between every run.

Top Fuel Engines

Top Fuel dragster engines must follow strict guidelines set by the NHRA governing body when competing in championship drag racing events in the United States and Canada. The most popular powerplant is a 7,500 to 8,000 horsepower crate-engine version of the Chrysler 426 cubic-inch, 90-degree V-8 Hemi. It is composed entirely of specialized, aftermarket, high-performance parts. It can be bored out to a maximum displacement of 500 cubic inches. The block is machined from forged aluminum, and the cylinder heads and connecting rods are carved from aluminum billets. The oversized valves, springs, retainers and rocker covers are made of titanium. The camshaft and five bearing crankshaft are made of billet carbon steel.

Technical Information

The typical Top Fuel engine displaces 496 cubic inches. They have hemispherical combustion chamber cylinder heads. The block and heads are usually made by Brad Anderson or Alan Johnson. The bore and stroke is 4.310 inches by 4.25 inches with a compression ratio of 6.5-to-1 or 7-to-1. The engine redlines at 8,250 rpm. Its intake valves measure 2.45 inches with 1.92-inch exhaust valves. The roller lifters are 1.68 inches in diameter with a valve lift of .8. Ignition is by dual 44-ampere, 50,000-volt magnetos. The engines use 42 mechanical fuel injectors with a mechanical fuel pump capable of pumping 100 gallons of fuel per minute. The engine is cooled by the massive amount of air and fuel mixture passing through it.

Supercharger

Top Fuel engines feature a 14-71 Roots style blower with a maximum manifold pressure of 65 pounds per square inch. It takes 900 to 1,000 crankshaft horsepower to run the supercharger. The blower has a rotor speed of 12,450 rpm and is capable of moving 3,750 cubic feet of air per minute.

Fuel

Top Fuel cars run on a mixture of approximately 90 percent nitromethane and 10 percent methanol called nitro. Top Fuelers burn nitromethane in an air to fuel ratio of close to 1-to-1. The viscous liquid is produced by adding nitric acid to propane. First formulated in the 1800s, the nitration process produces CH3NO2, which is used as an organic solvent in the chemical industry. Top Fuelers use up to 15 gallons of nitro per quarter-mile run at a cost of $18 per gallon.

About the Author

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