Another good article:
"Using measured torque and computer calculations, fuel-engine power is no longer a guess
For years, people have tossed around the figure of 6,000 as the amount of horsepower produced by supercharged, nitro-burning engines in Top Fuel dragsters and Funny Cars. And whenever that figure is mentioned, it is invariably followed by the caveat that it is an inexact number because no dynamometer can handle the output of such engines. So who needs a dynamometer? Using calculations and physical measurements, the overwhelming horsepower of fuel cars has finally been accurately determined to be a tick under 8,000.
Horsepower has been calculated using software and simple math formulas over the years, and, 10 years ago, 6,000 horsepower was an accurate figure. Racer Patrick Hale - mechanical engineer, president of Racing Systems Analysis, author of computer programs Quarter Jr. and Engine Jr., and consultant for race-car data analysis - has calculated horsepower in several National DRAGSTER articles in the past. In 1988 (one month before Eddie Hill ran the first four-second Top Fuel e.t.), Hale analyzed Hill's 5.066 record e.t. at the Gatornationals using the figures of car weight, tire rollout, wheelbase, and incremental times recorded by the track's clocks. Hale determined that Hill's engine produced 4,014 horsepower.
In late 1993, Hale used incremental times and other data from Cory McClenathan's 4.762 Top Fuel e.t. record, Pat Austin's 303.64-mph speed record, and Scott Kalitta's fastest-ever 308.64 in Topeka that fall to calculate the horsepower at 6,185. The e.t. decrease in those five years was a whopping three-tenths of a second. Speed, a reliable indicator of horsepower, jumped 22 mph, from 286 to 308. The increase in horsepower was 2,171.
Today, 10 years after McClenathan's 4.76 and Kalitta's 308-mph runs, the quickest e.t. has again decreased almost exactly three-tenths of a second and the fastest speed has increased 25 mph; 4.477 seconds and 333.91 mph are the best times ever turned by a piston-engine-powered car.
Hale crunched the numbers from Doug Kalitta's 4.486, 333.91-mph Houston run in April and determined the maximum horsepower to be 7,900, an increase of 1,715 over 10 years. Actual torque numbers that were recorded on Kalitta's hustling run and the calculated horsepower verify the accuracy of Hale's software-derived numbers.
Measuring for horsepower
Torque is measured; horsepower is calculated. Torque multiplied by rpm divided by 5,252 equals horsepower. The torque, or twisting motion, in this case is the output shaft that fits between the reverser and the pinion gear.
In addition to dynamometers, a transducer, or torque sensor in this application, can also measure torque. Torque sensors have been fitted to at least three fuel cars over the years: the Top Fuel dragsters owned by Connie Kalitta and Bill Miller and John Force's Funny Car.
Torque sensors are made of an almost impenetrable steel that can be designed in different shapes for different applications, but they all work the same way. Inside the torque sensor is a strain gauge with an output wire attached. A mechanical force applied to the torque sensor causes a subtle deflection of the strain gauge and a corresponding and linear change in the electrical resistance of the strain gauge."
Copyright National Hot Rod Association May 30, 2003